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1

The Pure Opportunity

The Far Eastern Obsession

The Western Renaissance

The Unique Image

The Designer’s Medium

The Richest Heritage

Main Index

The Pure Opportunity

Platinum’s origins in jewellery go back nearly 2,000 years to the

pre-Columbian Indian civilisations of South America.

Its modern tradition begins with the European court jewellers of

the 18th century and extends to the exquisite creations of the

great jewellers of the Edwardian era and the Art Deco period.

Today, it is used by jewellers around the world with skill and

inspiration to create dazzling innovations in jewellery technique

and design.

Contrast the shimmering brilliance of Japanese gem-set rings

and pure platinum necklaces with the subdued satin finish and

technical virtuosity of German design. Or compare the ice and fire

of Italian platinum and gold combinations with the novel mixtures

of materials and forms from the elite jewellers of New York.

Platinum jewellery, its markets, its image, its design and its

heritage - all can be your opportunities.

Index

2

The Far Eastern Obsession

The world’s principal platinum jewellery market is Japan.

Platinum, introduced after the Meiji restoration in 1868, rapidly

achieved a special position in the minds of the Japanese people

that remains unchanged to this day.

Platinum combines high quality, prestige and value with an

appeal, by virtue of its white colour, to traditional Japanese

modesty and sobriety.

The consumption of platinum metal by the Japanese jewellery

industry in 1980 was 14 tonnes; by 1999 it had almost tripled to

41 tonnes, and around 8 million pieces of jewellery containing

platinum were sold.

The rapid growth of the Japanese market has stimulated the

manufacture of platinum jewellery in other regions. Production in

Hong Kong, Thailand and India has increased for export to Japan

and the USA.

Lately, China has discovered the charms of platinum jewellery.

Demand for the white metal has surged in the 1990s, as young

urban Chinese women seek to acquire the truly modern styling

that platinum jewellery represents.

Index

3

World Platinum Jewellery Fabrication1990 - 2000

Japan

‘000 ozs

ROW Europe USA China

3,500

3,000

2,500

2,000

1,500

1,000

500

01990

19921994

19961998

2000

The Western Renaissance

Platinum jewellery in Europe existed in the 1920s and 1930s,

but virtually disappeared during World War II. Its post-war

resurgence began in Germany, where jewellers diversified out of

gold into platinum, introducing novelty to their product range and

profit from the higher added value of platinum jewellery. They

gave platinum a distinct identity characterised by stark modern

design and the prevalent use of a satin finish. Platinum jewellery

became established in the high-value sector of the German

market, acquiring an image of exclusive confidentiality, and today

encompasses the mass markets through more classical

platinum designs.

Italian jewellers began experimenting with platinum in the 1980s,

combining it with gold, creating warmth and softness around the

cool strength of platinum, imbuing each piece with characteristic

Italian sensuality. Expert at manipulating form, they have

achieved the illusion of volume without the corresponding weight

and expense and famed for their expertise in the design and

production of light pendant chains they now export all over

the world.

During the 1920s the United States was the largest consumer of

platinum for jewellery - the role of Japan today. Now, platinum

jewellery in the USA is undergoing a renaissance, begun by the

individual style and limited edition creations of New York

designers, and carried on by the appeal of platinum bridal

jewellery - the expression of a relationship which is pure, valued

and unique.

Index

4

Platinum Jewellery Demand 2000

China37% Japan

41%

ROW2%

USA12%

Europe8%

The Unique Image

Throughout the world, platinum jewellery is made in a purity of at

least 85 per cent platinum, and in Europe and the U.S.A., 95 per

cent is the norm. Contrast this with gold jewellery, sometimes as

diluted as 8 carat. The buyer of platinum jewellery will be aware

of another special aspect of the metal - its relative scarcity. Only

a little more than 150 tonnes of platinum were mined in 1999,

compared to 2,576 tonnes of gold and 27,626 tonnes of silver.

Because 50 per cent of the world’s supplies are consumed in a

variety of essential industries, the quantity available for jewellery

is not infinite. Many jewellers reflect this characteristic of rarity by

limiting the production of their platinum jewellery to just a few

examples of each design.

Technically, no other precious metal compares to platinum for

strength and resistance to tarnish. This is why silver was

discarded as the material for setting diamonds. Once the

technique of melting platinum in the workshop was established,

jewellers could use platinum’s structural strength and

untarnishable whiteness to show off diamonds at their best.

Today, the highest class diamond jewellery will usually be

mounted in delicate platinum settings to secure and preserve the

natural brilliance of the stones.

Platinum is not just for women. It is also ideal for a man’s

jewellery collection. Its cool, subdued look complements the male

psyche; discreet, elegant, imposing and strong.

Platinum need not be expensive to be special. As a young

person’s jewellery in a lighter style it still carries the mystique of

the rare and the valuable, the hard won metal which takes

10 tonnes of rock to be broken to produce a single ounce.

Index

5

The Designer’s Medium

The techniques for working gold jewellery cannot simply be

applied to platinum, which makes different demands on the

jeweller’s skills. Platinum requires a scrupulously clean working

environment, melting and casting equipment capable of operating

at high temperature (pure platinum melts at 1769°C) and careful

attention to polishing technique. Of course, there are superb

advantages in platinum too - it can be repeatedly heated and

cooled without the hardening and tarnishing effects produced in

gold alloys.

The techniques for working in platinum are already well

developed and, once mastered, allow free rein to the jewellery

designer’s imagination. Even the most slender sections of

platinum permanently retain their shape, giving the designer a

freedom not possible with other materials.

Perhaps the best modern example of platinum’s virtuosity is the

tension ring. A valuable diamond is secured by the pressure of

the ring shank alone. Only platinum, among the precious metals,

has the tensile characteristics that can achieve this effect.

Polished platinum provides a counterpoint to gold, the sharp

colour contrast of the two metals enhancing the beauty of each.

In platinum alone, the metal’s icy whiteness conveys its singular

message of brilliant elegance, and when understatement is

required, platinum’s true values can be concealed beneath a

subtle grey matt finish.

Index

6

The Richest Heritage

Platinum jewellery has a proud heritage. Cartier, Tiffany, Fabergé,

Van Cleef and Arpels, Buccellati, all have used and continue to

use and appreciate the fine qualities of platinum for men’s and

women’s jewellery of the highest character. The famed jewels of

the Duchess of Windsor were set in platinum. Platinum graces

the Crown Jewels of the Kings of England, the Tsars of Russia

and the Emperors of Japan.

Platinum, the metal which extends the boundaries of jewellery

design and amplifies the brilliance of precious stones, can add

value, excitement and prestige to your jewellery collection too.

Index

7

Duchess of Windsor wears a tiara inplatinum made by Cartier.

1

The Designer’s Medium

Platinum’s Qualities

Stone Set Platinum

Textured Platinum

Combination Platinum

Delicate Platinum

Modern Platinum

Main Index

The Designer’s Medium

Jewellery designers have a tough job. They have to come to

terms with one of the oldest human conflicts, that of art versus

commercialism. In the search for success, inevitably originality

and innovation have to be sacrificed in favour of ease of

production, practicality and consumer acceptability.

Platinum is probably the only material that can bring balance to

this conflict. The superior mechanical, chemical and commercial

properties it possesses permit the production of jewellery designs

which would otherwise stay on the drawing board.

Platinum’s unique blend of properties, unmatched by any other

jewellery material, offers the opportunity to reconsider design

concepts previously shelved because they are impractical in

gold or silver.

Platinum also offers unlimited scope to develop carat gold

designs by providing an attractive colour contrast as well as the

strength gold lacks.

Index

2

Platinum’s Qualities

It’s ductile . . . and can be extensively deformed, even in a hard

condition, without becoming brittle. Fine or detailed structures,

such as claw settings and filigree, can be worked without fear of

cracking.

. . . and tough, assuring long term shape and rigidity and offering

benefits such as secure stone setting and durable necklet or

bracket links.

It’s strong . . . structures have excellent shape retention even

when manufactured from thin sections, tubes or fine wire, and

even after soldering or annealing.

. . . even when hot, this strength doesn’t disappear and complex

soldering to a high degree of dimensional accuracy is possible

with minimal jigging or support.

It work-hardens quickly . . . so annealed structures can quickly

regain rigidity with little further working

. . . and has low spring-back, which makes it perfect material for

setting soft or brittle precious stones.

It’s oxidation resistant . . . even when soldering or annealing, so

component parts can be polished prior to final assembly. Intricate

designs where some parts are out of the reach of polishing tools

are thus achievable.

. . . and solders easily, leaving small, neat but strong joints ideal

for construction of delicate frameworks. Its low thermal

conductivity allows precise multiple stage soldering.

It’s modern . . . a variety of finishes expands the design options

even further. Polished, brushed, grit-blasted, hammered,

repousse and embossed finishes all retain platinum’s lunar-lustre

which combines perfectly with all the shades of gold, from red to

pale yellow.

. . . and has unlimited design opportunities, so when you next sit

down in front of a blank sheet of paper think what platinum has

to offer and stretch your imagination.

Index

3

Stone Set Platinum

Use platinum for setting all precious stones, not just diamonds.

Its brilliant whiteness and high reflectivity enhances their colours.

Its strength and low spring-back means that once bent into

position the claws (prongs) retain the stones securely, an

essential consideration when working with soft or brittle stones

such as opals or emeralds.

Textured Platinum

Even textured platinum has a lunar-like lustre. Try different

finishes to enhance jewellery designs. Brushed, grit-blasted,

hammered, embossed, granulated, repousse or chased finishes

are easy to apply using conventional techniques, even prior to

final assembly.

Combination Platinum

Use platinum in combination with any shade of carat gold from

red right through to pale yellow. The attractive colour contrast will

add an extra dimension to any design and platinum’s strength

can be utilised in areas where gold might fail.

Delicate Platinum

Use platinum to build delicate but rigid structures. Its strength

means that light sections can be used and its low heat

conductivity allows close proximity of numerous solder joints.

Modern Platinum

Use platinum’s properties to create innovative and original

designs such as the tension ring. Tension created by the

torque is strong enough to hold a gemstone as securely as

a conventional setting.

Index

4

Platinum - use it for all its worth

Glossary 11

1

2

3

4

5

6

7

8

9

Alloys

Casting/Melting

Handworking

Soldering/Welding

Finishing

Setting

Combination

Stamping

Machining

10Lasers

A glossary of terms used throughout The Technical Manual.

List of platinum alloy options and selectionguidelines reviewing the two major parameters,hallmarking and manufacturing requirements.

The investment casting process applied toplatinum, covering all aspects from model designthrough to recovering castings from investment.

Detailed information on how platinum can bedrawn, rolled and formed with ease usingrecommended annealing techniques.

Lists platinum solders that meet internationalhallmarking standards and describes solderingand welding techniques.

Techniques and materials designed to improvefinishing times and effects, including polishing,plating and texturing.

Describes techniques to produce various typesof settings in platinum including claw (prong),channel, pave and invisible varieties.

The fabrication of combination jewellery,techniques for the joining of gold and platinumand the finishing of combined metals.

The process techniques for stamping and diestriking, with advice on tool and componentdesign and material specifications.

Techniques, new tool materials and lubricantsthat will help minimise the problem of tool wear,and optimise machining efficiency.

How to assemble components, size rings withnear-invisible welds and repair potential rejectcastings using lasers.

Main Index

Alloys

Selection of Platinum Alloysfor Jewellery

The Manufacturing Process

Wrought and HandworkingFabrication

Solders

1

ManualIndex

Selection ofPlatinum Alloysfor Jewellery

Pure Platinumworks beautifully, it can be readilywelded andsoldered and takesa lustrous polish,but unless it isfinished in a heavilycold-worked state,it is too soft forhardwearingjewellery. Smallamounts of certainalloying elementscan give platinumthe properties that make it idealfor jewellery.

Choosing a suitable alloy depends on:

1. The method used to make the jewellery.

2. The market into which it is to be sold.

Items suitable for sale in one country may not

meet the standards of fineness required for

hallmarking by another country to be sold

as “platinum”.

Market Regulations

Most countries specify that for an item to be

described as "platinum" it must comprise not less

than 85% platinum.

Some specify how much platinum group metals

may be used in addition to a minimum platinum

content.

Some allow a small negative tolerance at the

nominal fineness levels. A few allow other marks

and fineness levels above and/or below 850 fine.

Hallmarking and other standards for platinum will

be dealt with in detail in a later section of the

manual but to make a first selection, alloys may

be grouped according to the fineness acceptable

in the country where the jewellery is intended to

be marketed.

Japan, China and Hong Kong

These countries allow 999, 950, 900 and 850

qualities. Japan allows a small (0.5%) negative

tolerance but China and HK do not. 900 fine

is the most common quality but in Japan 999

is commonly used for wedding rings.

United States of America

Items must contain a minimum of 50% pure

platinum and 95% total platinum group metals

(PGMs), to be described as platinum.

Above 95% Pt, they can be stamped

“PLATINUM” or “PLAT”.

From 85% to 95% Pt, the platinum fineness

must also be stamped, eg. “900 Pt” or “Plat

900” for a 90% platinum alloy or “850 Pt” or

“850 Plat” for an 85% platinum alloy.

From 50% to 85% Pt, all the PGMs

constituting and their fineness levels have to

be stamped,

eg.,”585 Plat. 365 Pall” or “585 Pt. 365 Pd”.

Only the USA allows “carat platinum” alloys.

Europe

Countries adopting the Convention of the

Control & Marking of Articles of Precious

Metals of 1972 are:

Austria, Ireland, Sweden, Denmark*,

Norway, Switzerland, Finland, Portugal*

and United Kingdom

Although these countries have previously used

a single 950 fine (no negative tolerance)

platinum standard they have recently

introduced 3 other platinum finenesses in

accordance with ISO recommendations. These

finesses are 850,900,950 and 999. Most

others, including:

Belgium+, Greece+, Spain+, France+,

Italy*+, Netherlands+, Germany and

Luxembourg

customarily use the 950 fine standard. Some

(*) allow small negative tolerances; others (+)

allow iridium to count as platinum. Germany

allows other finenesses for special

applications.

Alloys

Index

1.1

TheManufacturingProcess

The other aspectthat affects thechoice of a suitableplatinum alloy isthe method ofmanufacture of thejewellery. There aregeneral purposealloys but it is bestto select one thatis suited to casting,handworking orautomatedproduction,depending on which ispredominant in fabricating the piece.

Wrought andHandworkingFabrication

Even a 5% alloy addition can harden or improve

castability of platinum but, of course, there is

considerably more scope if regulations allow

greater additions, even if part of that must be

platinum group metals.

Table 1B summarizes the most commonly

available jewellery alloys. Melting ranges,

properties, density and other remarks are

representative of the nominal compositions of an

alloy type. The table does not give every minor

variation since small percentage changes required

to comply with marking regulations have a

minimal effect on the properties of an alloy.

Some countries allow a negative tolerance on the

fineness of the finished item and some do not, so

manufacturers may standardize their jewellery

alloys at slightly different levels. For instance, at

the popular 950 fine level, casting grain, or

wrought semi-finished products, may be supplied

at 960, 955 or 950 fine but they are all intended

to finish with nominal 950 level properties.

If the platinum jewellery market demanded, and

marking regulations allowed, the technology exists

for the leading precious metals suppliers to

supply alloys ready-made for a range of “carat

platinum jewellery”.

Casting

Cobalt and/or palladium have been used to

create casting alloys at various levels of fineness.

Cobalt suppresses oxygen levels in the melt,

improves fluidity and castability and gives a good

final hardness without reducing the melting range

significantly. Palladium produces a softer casting.

Copper alloy can also be cast if necessary but as-

cast surfaces tend to be rougher and more

difficult to polish than cast cobalt alloys.

Combining alloying elements can further enhance

particular properties. For instance, a combination

of 3% cobalt and either 2 or 7% palladium may

be used for 950 or 900 fine platinum to combine

good castability with a particular polishing ability

and colour. All of the casting alloys can be joined

to wrought components by either soldering

or welding.

Alloys

Index

1.2

Copper, cobalt, gold, iridium, palladium and

ruthenium alloy easily with platinum. Where the

hardnesses and ductilities in Table 1B are for

annealed materials, the differences between the

alloys reflect the hardening effect of the alloying

element itself. This affects the hardness of the

alloy in the annealed or “soft” state, typical at the

start of operations such as rolling, drawing,

stretching, stamping, texturing, soldering and

welding. Figure 1A shows that, of the platinum

group metals, ruthenium and iridium have a

greater hardening effect than palladium. It is also

possible to use limited amounts of non-platinum

group metals such as copper or tungsten; the

latter considerably raises the unworked hardness

and springiness for clasps, pins, bangles, and

complex stone settings.

General working platinum is said to workharden

rapidly compared with gold. Compared with

18 carat yellow gold alloy, this is true. It is

convenient for making strong finishing

components but requires increasing power and

more annealing stages. However, there is little

difference between the rate of work-hardening of

general working platinum alloys and typical 18

carat white golds. Figure 1B compares typical

results for platinum with only 5% copper, a

commonly used general purpose platinum

working alloy, with results for 18 carat white and

yellow golds.

Solders

The development of solders followssimilar lines tojewellery alloys butis furthercomplicated by theneed to achieveworkingtemperatures belowthe melting point ofplatinum and tomeet markingregulations.

Automated Methods

Palladium is used when an alloy with a

comparatively low rate of work hardening is

needed, eg. for high profile stamping; and there

is evidence that copper reduces tool wear. An

85% platinum/10% palladium/5% copper alloy is

used in Germany, Italy and Japan for the

Japanese chain market because of its balance of

softness without causing undue tool wear.

Figure 1A. Effect of different alloying elements on the annealedhardness of platinum.

Figure 1B. Effect of work hardening.

Usually, 3 to 5 solders form a range of working

temperatures to enable soldered joints to be

made efficiently at different stages of assembly.

Most platinum solders are mixtures of precious

metals, not always including platinum (but, if not,

then usually palladium) with melting ranges from

extra easy at about 950°C., to extra hard at over

1500°C. At the higher melting point end of the

range it is possible to accommodate more

platinum and so there is less risk of the solder

disqualifying a platinum item at the marking stage

and there is no need to use fluxes. Overuse of

solders is a common reason for an item to fail at

final assay. The best practice is to buy to a

manufacturer's specification and not to make

solders for platinum in-house; it is rarely

economical in the long run. There is already a

more than adequate range for jewellery purposes.

The use of up to 4 precious metals and

sometimes other metal components, means that

the total combinations of solders are too

numerous to classify in a simple table. So, Table

1A quotes a range typical of what is available

worldwide, but there are many variations.

Table 1A.

Solder Working Fineness FluxGrade Range ºC Precious

MetalsExtra Easy 935-955 950 RequiredEasy 1010-1029 950 RequiredMedium 1179-1217 999.9 Not RequiredMedium Hard 1319-1342 999.9 Not RequiredHard 1422-1445 999.9 Not RequiredExtra Hard 1519-1533 999.9 Not Required

Further Details

The choice of alloys outlined in Table 1A and 1B

are dealt with in more detail in the context of

each of the manufacturing processes including

welding and soldering, in later modules of the

manual. Terms printed in italics are also defined

in a platinum jewellery context in the glossary.

Alloys

Index

1.3

240

200

160

120

80

40

0 5 10 15

W

Co

Ru*

Cu

Ir*

Pd*

*Platinum Group Metals

% Alloying Element in Platinum

Har

dnes

s, H

v.

280

240

200

160

120

0 10 20 30 40 50 60 70% Reduction in Section% Reduction in Section

18ct White Gold: 750Au/125Ag/125Cu18ct Yellow Gold: 750Au/150Pd/100CuNiGeneral Working Platinum: 950Pt/50Cu

Har

dnes

s, H

v.D

uctil

ity

Table 1B. Outline properties of alloys for platinum jewellery, internationally.

Alloys

Index

1.4Composition: Pt/PGMs Melt Range Hardness Ductility Density Applications/Notes Countries % of Alloying Elements Fineness Solid Liquid Hv %Elongn g/cm3 of Main Interest

999 1773 1773 50 40 21.4 Stamped "Pt 1000" JAP

990 1773 1773 50 40 21.4 990 fine, chuk pak gam HK; EUR

5% Copper 950 1725 1745 120 29 20.0 Gen purpose, medium hard GER; HK; 108(C) can be cast. EUR

5% Cobalt 950 1750 1765 135 20 20.8 Fluid for hard castings GER; HK; EUR3% Cobalt/7% Palladium 900 1730 1740 125(C) - 20.4 Hard castings JAP5% Cobalt/10% Palladium 850 1710 1730 150(C) - 19.9 Harder castings JAP1.5% Indium/3% Gallium 950 1550 1650 225 26 19.3 Hard, springy, can be cast HK; EUR

5% Iridium 950 1780 1790 80 30 21.4 High work-hardenability for GER; JAP10% Iridium 900 1780 1800 110 25 21.5 safety catches, pins, GER; JAP; USA15% Iridium 850 1800 1820 160 15 21.5 springs, watch backs, JAP20% Iridium 800 1815 1830 200 10 21.6 fine wire work, chain, mesh GER

5% Palladium 950 1755 1765 60 22 20.6 Castings, delicate settings HK; JAP;68(C) 22(C) EUR

10% Palladium 900 1740 1755 80 22 19.8 General purpose in Japan HK; JAP72(C) 22(C)

15% Palladium 850 1730 1750 90 22 19.1 Chain making HK; JAP64(C) 22(C)

36.5% Pd/5% Copper 585Pt 1580 1650 160 - 15.4 Typical 14ct platinum USA950PGM

5% Ruthenium 950 1780 1795 130 32 20.7 Gen purpose, good machining HK; EUR; properties USA

5% Tungsten 950 1830 1845 135 20 21.3 Hardenable for springiness EUR; GER

NOTES: 1. Hardnesses and Ductilities in Table 1B are for the annealed state except those marked (C), which are for as-cast state.2. Pt/PGMs Finenesses are in Parts per Thousand.

Casting/Melting

Alloying, Casting and Melting

Arranging Wax Models forPlatinum Casting

The Investment Process

The Casting Process

Recovering the Casting

Good Housekeeping with Scrap

2

ManualIndex

Alloying,Casting andMelting

Casting is a basicmethod for makingclaws and headsettings, ringshanks with orwithout settingsattached, charms,chain links, braceletand brooch parts.

Follow the route:

• Select the pattern(s), usually metal originals.

• Form rubber about the pattern(s).

• Make models in wax.

• Design sprues in wax and build selected

models onto a wax base.

• Surround with a suitable flask.

• Invest with refractory slurry and de-air.

• Allow to set.

• Heat to dry, de-wax and preheat for casting.

• Choose alloy and weigh out charges.

• Melt, “stir” and superheat to casting

temperature.

• Spincast to preheated investment moulds.

• Cool whole cast mould.

• Knock out the castings while hot and

quench in water.

• Clean up and trim sprues from castings.

The use of platinum introduces nothing new in

principle nor in the sequence of operations. Most

platinum jewellery castings are custom-made by

specialists to clients' specifications and patterns.

But the precision casting of platinum is a logical

extension of skills for gold, and can be done on a

craft or small commercial batch scale. Casting

platinum is not difficult.

If a master pattern is common to both 18 carat

gold and standard platinum, the cast weight of

the platinum alloy will be about 30% higher than

for the gold.

Weight for weight, platinum alloy is 19.5 to

20.5 times heavier than the wax, depending on

the alloy.

With 18 carat gold, a 3% apparent contraction

compared with the master pattern is usually

allowed for the relative expansion/contraction of

the investment and gold alloy. Platinum requires

no such allowance because of the stability of the

special investment.

Platinum casting alloys offer a high degree of

fluidity to fill small sections and reveal textures.

In some respects, because oxidation and gas

resistance of platinum requires no fluxes or

degassing, the process is simpler than with

18 carat gold or standard silver.

Casting scrap may be safely recycled and even

100% scrap melt charges can be used.

It is the rapid loss of heat on casting that

presents the major difference.

This can be countered by:

• Careful sprue design.

• Using the most refractory and dense

investment.

• A high investment preheat temperature.

• Plenty of melting power, to obtain a higher

casting temperature.

• A high torque (acceleration) spinning arm.

Brief Reminder of Casting Alloys

Table 2A summarises the most commonly

available platinum casting alloys. Several more of

the alloys in Table 1B (Section 1) may be cast

although they were not developed specifically for

casting. Other casting alloys are available if

market demands and marking regulations allow

their economic use.

Cobalt alloys are preferred for rings, brooch and

bracelet parts because of strength and hardness.

Palladium alloys are softer and are preferred for

settings and delicate patterns. The cobalt alloys

are slightly bluer and the palladium alloys slightly

greyer than pure platinum.

Casting/Melting

Index

2.1

Arranging WaxModels forPlatinumCasting

Table 2A Outline properties of casting alloys for platinum jewellery.

Small-Scale Single LayerArrangement

There is no reason why a jeweller should not

cast, say, 35 to 70grams of platinum settings or

the parts of a ring or brooch, in a single layer on

a flat cone, using short, straight sprues (Figure

2A). This minimises the travel of the molten

metal during spin-casting and the distance of

feeding with still-liquid metal during solidification.

Figure 2A. A small arrangement of head settings where waxesspread from the wider part of the cone. Only about one third ofthe cone would be filled with molten metal but this would stillensure feeding with minimum scrap.

The cone is more a gate to the real casting space

than a reservoir of feeder metal. However,

sufficient metal is still needed to fill a proportion

of the base as well as the actual castings, to add

pressure when the metal is cast. If too much is

used, some is likely to splash back when

spinning. Platinum scrap can be remelted with

virtually no losses, but minimising scrap keeps

inventory costs down and the productive yield of

each melt high.

Medium-Scale BranchingArrangement

A more typical weight for a platinum jewellery

melt is 100 to 450 grams. If more is required in

one session, a number of moulds would be used.

Bearing in mind the high density of platinum

casting alloys (20 to 21 g/cm3) this may mean,

say, 10 - 20 head settings or 4 - 24 ring shanks.

These are normally arranged along branches off

the base, but mainly in a single layer (Figures 2B

to 2D).

Tree Arrangement

Waxes may be mounted in tree fashion where

there is the capacity for melting and casting

shots of 400 grams and over, but the same

"short distance" sprues still apply. A tree might

consist of a total melt of 900 grams with 500

grams in a central stem with short sprues off and

400 grams of castings. Although the stem may

be tapered a little to increase percentage yield,

this configuration tends to be less effective in

metal utilisation. Casts of up to 1 kilogram have

been made.

Casting/Melting

Index

2.2Composition: Pt Recommended Casting Temp Range ºC Applications/Notes% of Alloying Elements Fineness Large Castings ➔ Small Castings

100 1973 ➔ 2173 999.5 Fine PT5% Cobalt 95 1965 ➔ 2165 Fluid for hard castings5% Cobalt/5% Palladium 90 1935 ➔ 2135 Fluid for harder castings3% Cobalt/7% Palladium 90 1940 ➔ 2140 Hard castings5% Cobalt/10% Palladium 85 1930 ➔ 2130 Harder castings3% Cobalt/12% Palladium 85 1930 ➔ 2130 Med hard castings

1.5% Indium/3% Gallium 95 1850 ➔ 2050 Hard, springy, can be cast5% Indium 95 1965 ➔ 2165 No metal-mould reaction10% Indium 90 2000 ➔ 2200 Smooth, bright surfaces1.5% Indium/3.5% Palladium 95 1965 ➔ 2165 Finer detail

5% Palladium 95 1965 ➔ 2165 Softer castings, intricate settings10% Palladium 90 1950 ➔ 2150 Softer castings, intricate settings15% Palladium 85 1950 ➔ 2150 Softer castings, intricate settings5% Ruthenium 95 1995 ➔ 2195 Some roughness and difficult to

fill finest sections

Assemblies Versus IntegralCasting

It is sometimes better to design a piece in

sections and assemble them by soldering or

welding (Figures 2B and 2C). Cleaning and

polishing of separate parts may be more efficient

than with an integral casting (Figure 2D).

As with any jewellery alloy, platinum casting is

more difficult with:

• Long wire & tube sections,

• Large thin areas,

• Deep holes or cavities with small openings,

• Forms that curve back on themselves,

• Claws(prongs) thicker at the tips than the

base,

• Sharp inverted V-shapes.

Design should tend away from these extremes.

Figure 2B. A typical single layer set-up for ring shanks weighingabout 120 grams, contained in a 65mm circle by 45mm highwith its economical feeder head. It fits a standard 75mmdiameter by 100mm high flask.

Figure 2C. A group of claw/head settings for part-finishing andthen joining to shanks.

Figure 2D. Bulkier head settings cast integral with shanks.

Sprue Design.

Care at the wax arrangement and sprue design

stage minimises the proportion of process scrap

and scrap castings.

•It is often thought that platinum castings require

thicker sprues than gold, but if the correct

amount of superheat is used there is no need.

•The minimum sprue cross-section should not be

less than the largest cross-section of the

casting it directly feeds because the sprue must

freeze last to allow feeding to compensate for

casting shrinkage.

•Where sprues join, they need smooth fillets to

avoid turbulent metal flow.

•It may help to sprue a ring, offset tangentially,

or to several points at the edge of a horizontal

ring. Alternatively, two or three simple sections

may be cast in a stack and parted on a

lathe later.

Figure 2E. Examples of Sprue Design.

Casting/Melting

Index

2.3

The InvestmentProcess

Platinum alloys are cast at over 2000ºC into

investment moulds preheated to about 1000ºC,

so the most refractory, thermal shock and metal

penetration-resistant investments must be used,

such as those developed for stainless steel,

nickel or cobalt superalloy precision castings.

Investment Compounds

While gypsum-based investments (a refinement of

Plaster of Paris known as Hydrocal) are

satisfactory for silver and most gold alloys, they

are unsuitable for platinum due to lack of

refractoriness and sulphur contamination.

Platinum investment mixtures are normally the

phosphate type. They consist of a refractory flour

such as silica, mixed with ethanol, or acid

phosphate and magnesia, to form a pourable

cream. They are usually thixotropic with the

powder more difficult to wet uniformly and easier

to re-separate than plaster investments. They

need to be uniformly mixed using a dough mixer

rather than a whisk.

Investing

Attention to detail in investing the pattern is

important. Adequate vibration and vacuum de-

airing is needed to get rid of bubbles, particularly

from the surfaces of the wax patterns. The

subsequent drying out, dewaxing, burnout, firing

and preheat prior to casting differ, one formula

from another, for optimum results. For instance,

while a gypsum-based formula sets in about 6-7

minutes and may be dewaxed with steam, a

phosphate-based formula sets in about 14-18

minutes and, once set, should not be kept moist.

(Steam dewaxing of phosphate may not be

harmful but it does require careful control and

most platinum casters favour dry dewaxing.) A

gypsum binder may benefit from a retarder while

platinum investments may benefit from an

accelerator to speed up setting. Once started, the

burnout cycle should be completed or the flask

discarded. Avoid reheating a partially fired flask

from a previous day. With the removal of moisture

in the initial firing, the subsequent re-expansion

would probably cause serious cracking of the

mould and scrap castings. Details are important;

shortcuts should be avoided and the investment

manufacturer's instructions for a specific

investment should be followed closely.

A whisk is designed to introduce air into the mix

and although this may help mobility of the

investment to some extent, this is counter-

productive. The investment has to be de-aired

again in the short period between pouring and

setting. Finely divided air bubbles or foam is the

worst form to deal with and produces large

changes in volume between investment de-airing

and setting. A dough hook is mechanically more

satisfactory and introduces a more controllable

amount of air.

Flasks

Flasks must be made from metal that will

withstand many uses at the burnout temperature,

which is finally about 1000ºC. Stainless steel

may be used but flasks made from Inconel are

usually more economic, taking a balance of initial

cost and long life. Flask size is limited by the

clearances in the casting machine at its largest,

but it must be large enough to comfortably

contain the casting array, leaving not less than

7mm between the inside of the flask and the

nearest wax. Suitable flasks are supplied in a

range of sizes, typically 50 to 100mm high by

about 65 mm diameter for small machines, and

125 or 150 by 100mm diameter for large

machines, cut from 1.0 to 1.5mm wall tube, or

sheet, rolled and welded. The capacity of each

size of flask without patterns in place should be

noted so that a total amount of investment

needed for a series of casts can be estimated to

avoid shortfall or excessive waste.

Flask Lining

Until recently, most texts dealing with investment

for gold and silver jewellery casting advised that

an asbestos paper liner should be used on the

inside of the flask before pouring the investment.

This acted as a blotting paper during investment

and as a mildly refractory cushion against

Casting/Melting

Index

2.4

The CastingProcess

TemperaturesInvolved.The investmentassembly cannot bepreheated much over1000ºC, so there isa 750ºC gapbetween the freezingtemperature of themelt and theinvestment surface.This chilling factor ishigh and solidificationtime is typically onlythree or four secondscompared with goldat more than 20 seconds. With 18 carat gold thetemperaturedifference is onlyabout 300ºC, a much lower chilling factor.

expansion and shrinkage of the investment during

firing. Modern substitutes for asbestos paper are

available, but there is no need to use a flask liner

at all with the high refractory investments used

for platinum casting.

Reinvesting or Co-Casting with Platinum

The versatility of the lost-wax investment process,

and good hot strength and excellent oxidation

resistance of platinum jewellery alloys combine to

form an excellent basis for co-casting solid

platinum with another molten alloy. Probably the

commonest example of this in the past has been

to produce a gem setting in platinum, pre-polish

it and then attach it to a wax ring shank pattern.

This is then reinvested, preferably with the special

refractory mixture described above for casting

platinum on its own. The new wax is melted out,

leaving the platinum setting in place. Even

preheating prior to the second casting stage does

not oxidise the platinum alloy. When another

jewellery alloy such as molten 18 carat gold is

injected it solidifies in contact with, and welds

firmly to, the solid platinum alloy piece already

in place.

Many other combinations are possible, giving a

versatile style of design for combination jewellery

where marking regulations allow. This subject is

dealt with more fully in the section on

combination jewellery.

The best way to avoid premature freezing of

platinum alloy is to use a superheat of about

200°C for a heavy cross-section such as a

wedding ring blank, increasing to about 400ºC for

a light cross-section such as a diamond setting.

To find the casting temperature, add this

superheat to the liquidus temperature given in

Table 1B. This projects casting temperatures of

1850ºC to 2200ºC (see Table 2A).

Unlike most 18 carat golds, the difference

between the beginning (liquidus) and end of

solidification (solidus) for platinum casting alloys,

is only a few °C. They have a narrow

liquidus/solidus gap and freeze more like a pure

metal, so there is no difficult pasty zone feeding

that might lead to shrinkage porosity.

Melting

Platinum alloys are melted by oxy-fuel flame or

medium frequency induction melting. Butane or

coal gas may be the fuel composite but only

oxygen is capable of giving a sufficiently fierce

flame for melting and welding; air places too

much of a cooling burden. The hottest part of the

flame is just beyond the sharply defined inner

cone. It is possible to achieve a reasonably high

rate of melting with an oxy-fuel gas cutting torch

without using the supplementary cutting oxygen

supply. This is the main method used for castings

by the craftsman, usually with a spring-powered

vertical spin casting machine (see Figure 2F).

This is a cost-effective way of introducing

platinum casting to a manufacturing operation

traditionally dominated by gold production.

Figure 2F. Vertical spin casting machine.

More productive precision casting on a

commercial scale followed the development of

crucibles that would act both as a melting pot in

an induction coil and as a pouring ladle in a high

acceleration horizontal spin-cast machine.

Melting losses are low, melting is rapid given

plenty of power, and the melt is homogenised by

the induction current.

Casting/Melting

Index

2.5

Power/heat conversion can be as high as 95%

efficient. A 5kVA melting set is required for speed

of melting and good temperature control, for up

to 300 grams melts and lOkVA for melts up to

about 650 grams.

The Charge

It is difficult to guarantee homogeneity in small

melts starting with pure platinum and addition

alloy; particularly aiming at a precise fineness.

The safer practice is to remelt grain already to

specification, or chopped sheet/rod which will

have been homogenised by prior working. No flux

is needed when melting standard platinum

jewellery alloys because the melt does not

oxidise. It is rarely necessary to prod the charge

or stir the melt when using electric melting but, if

necessary, a refractory (eg., tungsten carbide or

fused~silica rod) stirrer must be used because

most metals alloy too readily with platinum.

Crucibles

Carbon based crucibles are not satisfactory

because platinum is embrittled by dissolved

carbon, so high temperature (up to 2300ºC),

refractory crucibles are used. Fused silica,

alumina or zirconia, (possibly with a cushion of

magnesia granules or a prefired internal glaze)

crucibles may be used, the choice depending on

the balance of cost and number of melts in one

session. As a precaution against thermal shock, it

helps to heat the crucible slowly for the first in a

series of melts; preheating in the burnout furnace

is useful provided the crucible does not contact

any residual wax. It does no harm to preheat the

first metal charge in the crucible at the

same time.

Judging When to Cast

Molten platinum, free from oxides and flux, has

very high emissivity. The photocell reading may

only be a guide to the right point to cast the

metal, aided by its colour as seen through

familiar goggles. It is essential to always use

adequate eye protection including ultraviolet and

colour filtration, to protect against remote

splashes or burning an image into the retina of

the eye. This also provides a consistent degree of

colour and intensity filtration for the judgement of

casting temperature. Even through dark green

welding goggles, the surface of the melt above

1800ºC is a glaring pearly white but, with

practice, it is possible to judge the difference

between nominal 1800, 2000 and 2200ºC.

Crucible life at these temperatures is short, so

platinum casting specialists prefer to bring the

melt up to about 2000ºC, hold on balanced

power while the mould is placed and then time

the input of power to a small or large degree of

superheat. Pouring is to a time signal rather than

at an apparent temperature. Older machines can

just melt a limited weight of platinum with full

power. As the casting temperature is approached,

heat losses just about balance the maximum

power input and the temperature ceases to rise

further. More recent machines have pre-

programmed power control with automatic

frequency tuning so that heat generates well

within the melt. The power is automatically

reduced as the pre-selected temperature

is reached.

Spin-Casting

The method that has produced the most

consistent quality is spin casting. This centrifuges

the dense platinum alloy quickly into the mould

to minimise premature cooling. Some machines

have an electronic controller that cuts off melting

power, lowers the coil quickly and powerfully

accelerates the spin arm carrying the preheated

mould. Machines have generally developed with

high acceleration and the necessary energy has

to be provided quickly at start-up. Nevertheless,

there can be too much acceleration and platinum

can impact beyond unrestricted sprues with

considerable force and produce a coarse finish

due to mould penetration. A useful compromise

is to use a horizontal sprue off the base and

steeply angled branches off either the horizontal

or vertical stems (Figure 2C). This achieves high

feeding pressure without direct impact.

Casting/Melting

Index

2.6

Recovering theCasting

When the casting array has solidified but not

cooled below red heat, the flask should be held

in tongs and the array hammered out and

plunged into cold water. This begins the process

of breaking up the residual investment around

the casting. Do not quench the whole flask,

even horizontally, red-hot: it may cause

a scalding eruption!

While flasks can be rounded again and re-used

many times, it helps to knock out the casting by

hammering the open ends rather than the flask.

High temperature investments are tenacious and

some or all of steam cleaning, hydrofluoric acid,

and grit blasting (alumina grit/glass beads) are

effective in removing them. A rough silicon

carbide grain can clean most surfaces while

smooth, ball-shaped grit is useful for compacting

and brightening surfaces.

Sprues should be removed as neatly as possible

to avoid lengthy filing. Short-nosed piano-wire

cutters shear through most sprues and pick off

other small nodules readily. A fine slitting disc is

useful if there is good straight access to the

sprue root; otherwise, a piercing saw may be

used. Specialist casters normally leave a residual

sprue root of about 1mm to be removed by the

client rather than risk undercutting the profile of

the component itself. Castings may be readily

joined to wrought platinum components and there

is no clear different technique between joining

castings to wrought platinum components and

the repair of castings. Minor casting faults can be

closed by welding. This can be done by reducing

a cut-off sprue to wire and using it as a weld filler

using techniques outlined in the section on

soldering/welding and lasers.

Most platinum castings are hand-finished; hence

the need for as good an as-cast finish as

possible. However, barrelling is possible using a

tumble-polisher with burnishing compound and

polishing shapes in much the same way as

for white gold - as detailed in the section

on finishing.

WARNING

Hydrofluoric acid (use 1 part to 3 parts water)

is a very aggressive liquid, which:

• Fumes even when cold.

• Corrodes through glass and most metals.

• Dissolves away residual investment.

• Can only be contained in lead, polyethylene

or paraffin wax containers.

• Requires containers with easily removable

covers.

• Must be handled with industrial grade

rubber or plastic gloves, wood or plastic

covered tongs.

• Must be washed off with plenty of water

after use.

Keep soda solution (100 grams sodium

carbonate in 4 litres of water) near to

neutralise any HF burns or smears and carry

out the whole process under a ventilated

hood. Use eye shields or protective glasses.

Casting/Melting

Index

2.7

GoodHousekeepingwith Scrap

• Always carefully segregate, package and

label cast trimmings, sprues and scrap

castings, by alloy type if not by job number.

• Re-melt any specific casting alloy with a

proportion of new grain or squares, but an

occasional all clean scrap charge is fine.

• Small amounts of a single, clean, general or

handworking alloy can be fused together on

a ceramic tile with a welding torch; forged,

reheated and used for small jobs such as

drawing or machining.

• Mixed, dirty or sweepings type scrap is best

returned for refining. It may first be burnt off

and steel filings/grindings removed with a

magnet, except with Pt-Co alloys which

are magnetic.

Keep a Record of Your Process

Platinum alloys are valuable and should not be

mixed indiscriminately, either as good product or

as scrap. All production should be recorded with

job number, pattern configuration, alloy, casting

temperature, weight yielded and notes of the

results. Batches of castings and scrap should

also be correspondingly labelled with the job

number. Good records build up good experience

for successful repeats and identify "lessons learnt"

and economic recovery by minimising scrap.

Casting/Melting

Index

2.8

Handworking

Handworking of Platinum

Specific HandworkingProcesses

Platinum Working Equipment

3

ManualIndex

Handworking ofPlatinum

Mechanical workingof platinum jewelleryalloys, whether byhand for individuallycrafted pieces orsmall batches byspecialistmanufacturers tocatalogue designs,is similar to theworking of mostwhite golds. Foreconomic reasons,most workers preferas smooth a surfaceas possible ratherthan remove metal.It is very importantto maintaincleanliness to avoidcontamination thatleads toembrittlement,particularly whenhot-working.Otherwise hot andcold working arestandard. Platinumalloys are oxidationresistant, formableand easily annealed,but die and toolwear can be aproblem for thelarge scale producerif suitableprecautions are not taken.

Hot-Working

At its simplest, an alloy is hot-worked above the

annealing temperature so that any work-

hardening is relieved as quickly as it is generated.

Hot-working is best if economic batches have to

be subjected to considerable reductions or

repeated shaping blows. There are no significant

problems in hot-working normal platinum

jewellery alloys. Even casting alloys can be hot-

worked. A typical example of hot-working

platinum is the open die forging of 5kg cast

ingots of chain-making alloys at 1100 to 1200ºC.

Reductions of up to 70% may be made between

reheats to form slabs for thin strip rolling or bars

for wire drawing prior to automatic chain making.

Cold-Working

The general annealing temperature for platinum

alloys is about 1000ºC and the jobbing jeweller

rarely needs to work them so extensively that

prolonged or repeated heating above 1000ºC is

justified. Cold-working and annealing is normally

preferred because it more accurately controls the

properties of the piece prior to joining and

polishing. Such cold-working operations include

rolling, section-drawing, hammering and pressing.

A few platinum alloys work harden fairly rapidly

and the work necessary to continue deforming

those that start off relatively hard is significant;

cracking is less of a problem.

Figure 3A shows examples of some 5% and 10%

alloys of platinum compared with a typical

18 carat gold alloy. Alloys like platinum-palladium

have a lower rate of work-hardening. With most

platinum jewellery alloys it is possible to make

reductions in cross-section of up to 70% between

anneals if there is adequate power. For good

repeated practice it is better to choose

reduction/annealing sequences to suit each alloy

and so control grain size and mechanical

properties. Normally, reductions of less than

30% between anneals should be avoided

because a combination of light cold work and

frequent anneals can cause coarse grain

growth and corresponding orange peel surface

effect. In most cases, though not all, this is

undesirable because it complicates the finishing

and polishing of the piece.

Figure 3A. Rate of work hardening of several (initially annealed)platinum alloys.

When cold working platinum:

• Keep all tooling clean

• Do not use excess lubrication

• Keep roll surface and dies highly polished

• Clean drawplates of beeswax, other

lubricants, and metal particles that could

damage a high finish

• There is a tendency to smear or drag wear

on working tools

• Keeping a high tool polish minimises wear.

Annealing

Almost all platinum jewellery alloys resist

oxidation during annealing and either

conventional torch flames (air- or oxy-fuel gas) or

electric furnace annealing may be used. Furnace

annealing allows better control of the level and

evenness of temperature and, in turn, the

mechanical properties of the component. Most

cold worked alloys begin to stress-relieve at

600ºC (dull-red) and they soften rapidly at

1000ºC (bright orange) which may be regarded

as the general annealing temperature. Because

of the speed and ease of annealing and oxidation

resistance, many workers use a gas torch for

inter-stage anneals.

Handworking

Index

3.1

Where very thin, heavily cold-worked or highly

stressed sections are to be annealed it is

advisable to stress-relieve by heating for period

of a few minutes at 500 to 600ºC before full

annealing or strongly heating for soldering or

welding. Time at the full annealing temperature

will depend on the thickness of the section, but

1 minute per mm of section thickness should

be sufficient for thicknesses up to about 5mm.

Too frequent annealing or annealing for too

long can cause grain growth which may make

subsequent working or polishing to a smooth

surface more difficult. Except for platinum-

ruthenium, platinum alloys do not generally age

harden and so can be either cooled in air or

water quenched from the annealing temperature

without harm.

Contamination

Platinum combines with most molten metals.

While this is useful for making alloys with

controlled characteristics, it can also cause

trouble. For instance, small amounts of

aluminium, lead or tin can cause low melting

point compounds with platinum and this can lead

to intergranular cracking called hot-shortness

(silver, indiscriminately alloyed with platinum

can cause intergranular cracking, but this is

very unlikely under ordinary annealing

conditions). Intergranular cracking is more likely

to be caused by arsenic, boron, magnesium, or

silicon. While it is not common, it is possible, in a

reducing flame during melting, joining or

annealing, to liberate aluminium or silicon from

refractory materials such as crucibles or support

bricks, or carborundum (silicon carbide)

abrasives. This can only occur under reducing

conditions, when the platinum alloy is in close

contact with the support, well above red heat.

Hydrocarbons such as oils or grease are typical

contaminants that can give rise to unexpected

reducing conditions. It is important to avoid

trapping potential contaminants in the metal

during working processes such as rolling, drawing,

hammering, cutting or abrading. Good

housekeeping prevents these potential

problems by avoiding contamination.

Most metal contaminants of platinum surfaces

may be removed by pickling in hot, but not

boiling, 10% nitric acid, prior to annealing. Iron

contamination is best removed with hot

hydrochloric acid.

If contamination has occurred after heating, it is

very difficult to correct other than by cutting it out

and repairing by joining in a new piece of clean

alloy. Attempts to solder intercrystalline cracking

or to dilute the effect by annealing usually results

in spreading the problem.

Handworking

Index

3.2Annealing Temperature Guide

For most metals and alloys, the annealing temperature in °C is a little over half the melting point in ¡Kelvin. (Add 273 to the normal melting point in ºC., to get ºK.)

mptºC mptºK AnnealºCStandard Silver 890* 1163 5819ct Gold 800-960* 1153 577 about14ct Gold 850-920* 1158 579 600ºC18ct Gold 900-990* 1218 609Pt 1000 fine 1773 2046 1023Pt 585 fine 1580 1853 927Pt-5%Cu 1725 1998 999Pt-5%Ir 1780 2053 1027Pt-5%W 1830 2103 1052Pt-10%Pd 1740 2013 1007

*mpt varies with ratio of the other metals alloyed with gold.

Annealing temperatures are not exact; they vary in practice with annealing time and with the amount of prior cold work. Heavy work at low temperatures lowers the normal annealing temperature. Except for the extremes ofcarat platinum alloys at the low end & Pt-Ir or Pt-W alloys at the high end, an annealing temperature of 1000ºC is adequate for most purposes.

}

Some Possible Causes:

• Lead-Tin solders on the same work bench

• Charcoal soldering blocks

• Abrasives rolled into the surface

• Filings from other precious or non-precious

metals

• Filings or drillings from gemstones or

mineral crystals

• Oils, grease or soaps used for drawing,

rolling, etc.

• Machining suds (lubricants)

Some Preventatives:

• Avoid reducing flames and furnace

atmospheres

• Use oxidising conditions; platinum itself will

not oxidise

• Avoid trapping contaminants in platinum

during working

• Degrease and positively clean surfaces

before heating

• Avoid contaminated supports during heating

and joining

• Prefer refractory supports to charcoal

when joining

SpecificHandworkingProcesses

Forging

The term "forging", while metallurgically correct,

sounds heavy for jewellery processes. It covers

squaring or rounding by planishing, spreading

widthwise, (Figure 3B) tapering/pointing (Figure

3C), or upsetting the cross-section of the

jewellery component, usually between a smooth

faced hammer and an anvil or stake or swaging

between open or closed dies. Much the same

principle applies in ring forming, forming tube

sections, and on a small scale, hammer

texturing, embossing and chasing. Platinum is

very malleable and forges well, but it does require

deliberate and forceful blows especially when

dealing with large cross-sections. A good

indication of its malleability in the annealed state

is that strip sections up to 3 or 4mm thick can

be folded double and compressed by hammering

without cracking. In fact, this is a good way of

combining the excellent strength of cold-worked

platinum in thin sections, with bulkier sections

achieved by folding and hammering without

soldering or welding (Figure 3D).

Figure 3B. Spreading platinum strip widthwise using a thinnedand polished cross-peen or small raising hammer to movemetal outwards at right angles to the long axis of the piece. Theback of the hammer head needs to be weighty to provide force.

Figure 3C. Tapering/pointing a section. Hammer moves in aconstant short arc, finishing normal to the taper angle(otherwise, a square section will offset to one side to form arough rhomboid shape). Work may be rotated radially beneaththe hammer blows to achieve pointing (all round tapering) forstart end of section drawing.

Handworking

Index

3.3Contamination

To maintain good shape control, use square or

radial blows as appropriate; otherwise the

section tends to offset to one side or the other.

Once the near final dimensions are achieved, the

section can be trued by planishing, die drawing or

even rolling. It can of course be finished by filing

but it is always preferable to use compression

processes to conserve metal weight and minimise

the need for extensive surface finishing.

Anneal after about each 30-35% reduction in

cross-sectional area even though platinum will

usually withstand greater reductions without

cracking; its workhardening ability is such that it

requires considerable increases in force to

continue working. Heavily work-hardened

platinum alloys can dent stake, anvil and hammer

surfaces, making it progressively more difficult to

maintain a good surface finish on the work.

Figure 3D. Platinum strip/tape can be repeatedly doubled backon itself and, in effect, cold forged to produce a thick section(which may then be locally annealed, if required) attached to afiligree section (which may be left cold-worked).

Section and tubular section drawing

With draw plates, channelled and taper-ended

platinum strip can be formed into more precise

channel sections, hollow ring stock and seamed

tube (Figure 3E). Thin rod and wire can be

modified to many different cross-sections.

Prepolished dies are available commercially, but

some craft jewellers prefer to draw simple

sections through a hand-made draw plate. This is

still possible with platinum, but time consuming if

complex sections are attempted. The limiting

factor is the smearing ability of platinum on

insufficiently polished die surfaces or where the

interface pressure is very high such as at tight

corners and re-entrant sections. While hand-

made draw plates may be satisfactory (with acid

cleaning) for an occasional piece of craft jewellery

in platinum, economic batches demand best

quality tungsten carbide drawing dies kept in a

high state of polish, particularly in the work zone;

otherwise platinum will further roughen the

surface and lead to platinum build up and loss of

cross-sectional accuracy.

Figure 3E. Starting a thin walled tube from strip with a taper cutsmoothly at the lead end, hammered into a channel to startcurving the tube wall and completed by die drawing (with seamwelding if necessary).

Reducing tubular cross-sections with the wall

finding its own thickness is known as sinking

(Figure 3F). This is a simple variant on wire

drawing and wire drawing dies may be used.

Where the wall has to be controlled for short

platinum hollow sections for jewellery it is

convenient to use a mandrel. This is a polished

steel rod or hard-drawn wire (piano wire as

slender as 0.5 mm diameter may be used)

whose external shape matches that of the

required internal cross-section of the platinum

component. The mandrel is placed inside the

starter tube and the two are co-drawn through

the die sequence. In the first few passes the

mandrel is loose inside the platinum, but after

being drawn down onto the mandrel the platinum

wall is controlled between the mandrel and the

die. The total reduction in the wall cross-sectional

area between anneals should be limited to about

35%, particularly after the platinum is in full

contact with the mandrel, so an inter-stage

anneal before the platinum grips the mandrel is

advisable. The mandrel must start with a length

greater than the finishing length of the platinum

tube or it will be enclosed. The mandrel also

introduces another dragging friction interface

that, with platinum, requires careful lubrication

and techniques to remove the mandrel.

Handworking

Index

3.4

Figure 3F. Tube sinking with relative wall thickening compared tomandrel drawing for short lengths. the mandrel controls the wallthickness and also takes part of the load at the short end.

Lubrication and mandrelseparation

A hard soap such as “Pale curd industrial” in bar

or powder form is used on the die and the

mandrel for lubrication and to ease the removal

of the platinum tube after drawing is completed.

Bar soap can be applied to a stout mandrel by

rubbing; soap powder can be tapped into the

tube bore prior to mounting on the mandrel. To

get a better finish, particularly on the outside of

the finished section, it helps to use a soft soap

lubricant for the last two or three passes.

Figure 3G. Loosening the mandrel by tapping with parallel barsor “castanets”.

Attempting to drag the mandrel out of the tube is

likely to tear or buckle the platinum. To free the

tube from the mandrel after completing the final

pass, it must be burnished off with one or two

passes through rolls that just pinch across a

series of outer diameters and impart a slight

degree of twist. In effect, the tube wall is slightly

expanded away from the mandrel. For occasional

short lengths, it is possible to achieve the

roller/twist effect with a pair of parallel tool steel

rods (or tungsten carbide for very long life)

gripped in a handle with a gap just a little larger

than the outer diameter of the platinum tube to

be removed. These are “played like castanets”

along and around the mandrel/tube combination

to achieve many small pinching blows to loosen

the tube (Figure 3G). The loose tube, now off the

mandrel, may be given a finishing pass through

the last die hole again to clean up the surface

and shape.

Spinning and Doming

The ductility of platinum makes it quite amenable

to spinning. The jobbing jeweller is unlikely to

need to spin large pieces into deep shapes but, if

so, the most ductile alloy is preferable to avoid

the need for too many annealing stages. Virtually

all alloys can be spun to produce shallow dished

shapes for jewellery pieces in a single stage. The

metal is worked against a former at a shallow

angle and the strain is not severe. Relatively deep

pieces may need two stages with an interstage

anneal, mainly to reduce the off-centre pressure

to be exerted by the burnisher (Figure 3H).

Making small round shapes up to hemispherical

depth is best accomplished by doming. Platinum

jewellery alloys respond well to this technique.

Indeed, doming of a blank, and perhaps

annealing, may be useful as a start to spinning.

Some of the larger scale (deep drawing and deep

spinning) or more continuous working processes

(stamping), and processes like ring sizing more

akin to finishing operations, will be dealt with

later in the Manual.

Figure 3H. Outline sketch of small scale spinning arrangementfor making a collet for a stone setting from a sheet-circle usinga burnisher. The bottom section may be parted off and may beuseful as a bezel ring.

Handworking

Index

3.5

Cutting

One of the most frequently used processes in

handworking a piece of jewellery is cutting to

shape or length, by piercing and sawing, slitting,

drilling, filing or grinding. On a small scale, there

is little need to differentiate between tools,

grades and techniques for white gold and for

platinum. It is always worthwhile minimising the

amount of metal removed or scrapped, by

carefully sizing the piece to minimise or eliminate

the need for cutting. Often, platinum wires, tubes

or strips will be thin, taking advantage of high

strength. As with any hard jewellery alloy, it is

unwise to cut thin sections with coarse settings.

Jewellers' (tool steel) saw blades are rated from

8/0 for the very finest pierced work, through 0,1

and 2 which are better for silver but too coarse

for most platinum jewellery work, and on up to

size 8.

Platinum alloys appear to wear out saw blades

and similar hand tools more quickly than do gold

or silver. This is because the alloys cold weld very

well. Metal builds up on cutting edges, followed

by stick/slip binding/removal of the debris, and

this causes extra wear. Figure 3I sketches the

different effects between aluminium, gold/silver,

and platinum alloys on a coarse saw blade.

Compromise between too smooth and too

coarse. Use around 3/0 grade which is a good

general purpose blade for white gold and

platinum. The blade should travel at a fairly flat

angle (about 15 degrees or less) to the cut

surface to avoid excessive snagging at the leading

edge. Filing should also be done at a similarly flat

angle with frequent changes of the file surface

and cleaning. The lubricant "oil of wintergreen"

has been proven to be effective in relieving wear

on files.

“Sanding” papers should be chosen for their free-

cutting ability, in which case the abrasive particles

will remain upright on a stiff bonded backing

paper. 240 and 400 grades are usually adequate

in two stages. It is often better to part off

platinum sections with thin alumina or silicon

carbide disks running at 1300 to 3800 M/min.

peripheral speed rather than use a lathe tool

which tends to leave a coarse burr and

undergoes rapid tool wear.

Figure 3I. Sketch of different modes of debris buildup/clearance on a jewellers’ sawblade.

PlatinumWorkingEquipment

Ideally, rolls, dieplates, dies, saw blades, chasing

tools, files, grinding wheels, and similar tools

where there is a degree of sliding movement

during working, should be kept specifically for

platinum alloys only. This is because platinum is

more vulnerable to contamination from other

metals picked up under working conditions.

Polished hammer and stake faces cause fewer

problems because the impact is normally square

rather than sliding. Large platinum jewellery

producers, in Japan for instance, dedicate separate

parts of the same factory, let alone separate

tooling, to platinum or gold jewellery production.

If this is not economical, then the best

alternative is to apply good housekeeping and

segregate tooling used for platinum; clean it

and the working areas before and after

platinum working. This ensures maximum

recovery of platinum scrap and sweepings and

minimises cross contamination of platinum. For

instance, when the same rolls are used for

platinum and other metals, platinum should be

placed in 10% nitric acid at 70ºC to remove any

residues of other metals before any annealing or

joining process.

Handworking

Index

3.6

Soldering/Welding

Joining Processes

Welding

Soldering

Eye Protection

4

ManualIndex

JoiningProcesses

Platinum jewellery alloy components may be

joined efficiently by:

• Fusion welding

• Pressure or friction (dry) welding

• Spot-welding

• Laser-welding (See Chapter 10)

• Soldering

• Mechanical processes such as rivetting

• Powerful adhesives.

Since platinum alloys do not oxidise, fusion

welding and soldering are straight-forward

extensions of traditional precious metal joining

processes and so they predominate for platinum

alloys too. The good hot strength and oxidation

resistance of platinum alloys allows them to

stand up to intensive local heating in welding and

soldering, without need for extensive jigging which

would otherwise restrict access and remove heat.

There are no adverse reasons, apart from lack of

familiarity or the wrong scale of working, why

other joining processes should not be used.

Platinum welds readily to itself by hammering,

friction and upsetting, electrical resistance spot-

welding and laser welding, but components may

need to be selected or designed to take full

advantage of such processes. For instance,

friction welding tends to be more economic as a

medium scale batch process, while hammer

welding is a satisfying craft technique for chunky

rather than filigree work.

Heat Sources

Most soldering and welding operations on

platinum jewellery alloys are carried out at

temperatures above 1500ºC and often near

2000ºC, so an oxy-fuel gas flame or electric arc

must be used. While the electric arc (including

TIG welding) is used in fabricating platinum for

chemical and similar industrial applications on a

medium scale, it is not usually appropriate for the

jewellery manufacturer or craftsman. On the other

hand, the non-oxidising nature of platinum allows

burners to be designed to give a very precise

bright hot flame using a little excess oxygen. With

practice, these can be used with pinpoint

accuracy on platinum jewellery pieces either for

welding or soldering (Figure 4A).

Order of preference of fuel gases with oxygen

for platinum welding/soldering:

Hydrogen 1

Propane, C3H8

Butane, C4H10 2

Natural Gas, CH4+C2H6

Acetylene, G2H2 3

based on risk of carbon pick-up. Even

acetylene is OK with excess oxygen.

Small flames need a low oxygen pressure under

tight flow control, otherwise the flame will lift off

the torch tip and extinguish. This may need an

additional low pressure regulator working at about

1 to 2 pounds pressure mainly to regulate

volume flow. As with all precision oxy-fuel gas

flame control, the nozzle-tip sizes need to be

matched with a particular fuel gas and its

corresponding oxygen ratio.

Platinum jewellery lends itself particularly well to

soldering or welding using an oxy-hydrogen flame.

The gases may be supplied from pressure bottles

but they may also be generated in situ by

electrolysis. There are transportable units (Figure

4B) that use potassium hydroxide solution as the

electrolyte, which is split (only the water) into

hydrogen and oxygen which are fed separately at

low pressure to well designed burner jets. These

can produce an initially neutral flame so small

(22 gauge jet) as to precision weld a narrow

platinum band for sizing, or at the large extreme

(13 gauge jet), melt more than 50 grams of

platinum scrap. The rate of burning at the jet

determines the pressure in the reservoir system

which, in turn, controls the rate of electrolysis.

The temperature of the flame can be lowered and

the luminescence increased, by allowing the gas

to pick up small quantities of volatile organics,

such as methyl alcohol, methyl ethyl ketone

(MEK), or acetone. The Williams Oxyflame

Soldering/Welding

Index

4.1

}

Soldering system uses hydrogen peroxide and a

catalyst to generate oxygen and water. The calor

gas burns in oxygen from a small canister to

give another completely portable (no

electricity) version.

Figure 4A. (Annotated) sketch of parts of a typical oxy-fuel gasflame. Above: complete flame profile; below: close-up showingcombustion zones.

Figure 4B. Self-contained oxygen hydrogen generator set:Microwelder.

Welding Apart from the high temperatures involved,

platinum alloys weld readily without the need for

fluxes. Because filler metal, if needed, is the

same as the components to be joined, it is easily

possible to close the seam without any visible

colour change. This is a decided advantage in

sizing rings, for instance. Even so, it is good

practice to minimise the amount of filler

needed (whether welding or soldering) by

making joints as closely and accurately as

possible; platinum alloys do not readily bridge

large gaps with filler metal (which is not pasty

at any stage).

If the joint is made tightly, the only filler metal

needed is a thin piece (0.1 to 0.5mm) of the

same alloy cut to just outside (say 0.5 to 1mm)

of the two sections (in ring joining, the two are

likely to be the same section anyway) and this

avoids any contraction of the whole joint.

The two components to be joined are clamped on

either side of the (vertical) filler and the whole

joint is heated slowly, beginning with the heavier

sections on either side and gradually moving the

torch flame to concentrate on the fringe of filler

metal. The filler should melt down into the joint

before the two components fuse any more than

superficially at the interface. Remove the flame

as soon as fusion has taken place. If the joint is

longer in one direction, like a seam, the filler will

be a small strip with its long edge pointing along

the seam, but still horizontal; concentrate on one

end first and as fusion begins, move slowly along

the joint. If the seam is extensive, it is possible to

use a thin wire filler pointing into, from ahead of,

the flame. When welding or soldering, support

the work on lightweight refractories such as

Chamotte stone and avoid carbon bases such

as charcoal.

Figure 4C. Platinum ring sizing/welding. A & B: tight set-up ofjoint and filler; C: heat either side and then D: onto the fillerwith hottest point of the flame; E: shallow profile of the finishedjoint prior to smoothing down.

Because platinum has relatively low thermal

diffusivity, the heat tends to stay concentrated

near the point of application, unlike gold and

silver where the heat is conducted away readily.

This helps control the size of the joint and

Soldering/Welding

Index

4.2

simplifies making multiple joints in the same

piece of jewellery. The joint should finish with just

the smallest "bulge" of matching colour which can

be smoothed down to the original cross-section.

This technique is well suited to joining relatively

heavy and particularly matching sections such as

ring shanks, shanks to head settings with

shoulders, bangle sections, and pendant and

brooch parts.

Warning

Even with very small oxy-gas flames capable of

dealing with small sections of platinum, never

attempt preheating, let alone welding, without

using properly selected welding goggles. The

heat builds up in thin sections very quickly and

the radiation emitted over 1000ºC is likely to

cause eye damage; radiation at the melting

point is certain to cause damage to the

unprotected eye.

On the other hand, it is not so easy to join thin

sections of platinum this way because the heat

will build up very quickly in exposed sections of

the order of 1mm thick or less and lead to

premature melting. This may be overcome by

using fine oxy-gas flames to fuse into a tiny bead,

thin wire sections that have already been pinched

or twisted together without any additional filler.

Wire as fine as 0.3mm can be welded if a small

enough flame is used.

Because platinum has low heat conductivity, it is

possible to make good repairs without damaging

either set stones or the surface finish of the bulk

of the piece. Obviously, one should avoid playing

the flame on any stone at all and keep well away

from sensitive stones such as opal. Traditional

ways of protecting stones with heat sinks such as

a wad of wet cotton wool should still be used.

When planning a repair on a platinum piece,

welding can be very useful in avoiding colour

mismatch, but it is wise to consider whether

there has previously been soldering near to the

proposed repair site. If there has and welding is

carried out close enough to allow significant heat

diffusion, then there is a danger that the

previously soldered joint will give way. If so, a

solder repair is preferable.

Figure 4D. Sketch of a seam weld with (i) strip filler in place,and, (ii) filler wire fed towards the flame; both moving awayfrom the already welded zone.

Laser Welding

(See Chapter 10).

Friction, Spot and Stitch Welding

Freedom from oxidation at high temperatures, the

tendency to smear by dragging at a platinum

surface and the need for very little additional

deformation, makes platinum an ideal material

for friction welding. In this process, a stud-like

shape is rotated under light pressure against a

flat surface to generate friction and heat. At an

appropriate temperature (which with platinum is

theoretically cold welding) the rotation is stopped

and pressure is applied to weld the two

surfaces together.

Figure 4E. Outline diagram of (small-scale) spot welder set-upwith schematic of the weld cycle characteristics.

Spot welding is usually achieved by electrical

resistance heating at an interface, with the power

led in through stout electrodes that are also

capable of delivering a punch pressure to finish

the weld. Stitch welding is, in effect, an

overlapping series of spot welds, and in both

Soldering/Welding

Index

4.3

cases, the timing of the whole process is

electronically controlled (Figure 4E).

Again, these processes are more compatible with

batch production of simple jewellery operations,

such as joining studs to front designs in earrings

and bosses to brooches, rather than a one-off

craft approach.

Soldering Platinum components may be soldered readily

with a wide range of solders, some of which can

be worked at temperatures low enough to use a

gas-compressed air torch. However, to obtain a

better colour match, it is advisable to select

solders that also include platinum, and some of

these flow at temperatures only achievable by

oxy-gas flame melting. This is the method

assumed in the following section. Otherwise,

sound joining of jewellery platinum components

is simply dependent on good standard

soldering practice:

• Design for good soldering

• Fit the parts as closely as possible

• Use the minimum amount of solder

• Use a precise, oxidising flame just large

enough for the job

• Keep the joint and its surroundings clean

• You may not need a flux

• Parts may be prepolished before joining.

Platinum jewellery alloys retain their shape near

their melting points, so jigging is not difficult. Use

low thermal capacity jig parts not too near the

joint area and confine the flame close to the joint

with the solder in place. Use many small pieces

of solder uniformly along the joint rather than a

few large pieces. In this way the solder will flow

only where it is needed and heating should be

stopped immediately flow occurs; no extensive

preheating or any post-heating of the

components is necessary.

Keep the jig clear of the flame to avoid

contamination with, for example, iron binding

wire, dirty steel clips and charcoal supports.

Most of what has been said about avoiding

contamination in annealing and hot working of

platinum applies to soldering too; no

carbonaceous substances, borates, or silicon

under reducing conditions. Attempts to solder up

cracks or join parts broken due to contamination

usually spread the problem rather than cure it.

The highest in a suitable series of solders flows

about 100ºC below the melting point of the

corresponding platinum alloy. There are roughly

100ºC temperature differences between the

solders in a given series so this allows

considerable flexibility during multi-stage soldering

operations. (See the section on solder

compositions).

The wettability between platinum and solders is

excellent, so there is no need to use excess.

Another reason for limiting the amount of solder

is to minimise the mismatch in colour in the

resulting joint. Some solders, the low-platinum,

low melting point ones in particular, differ in

colour from the platinum alloy components, and

diffusion of platinum back into the joint is low so

the colour is not affected by the platinum in the

body of the jewellery. As a general rule, solders

with the higher melting temperatures give the

nearest colour match to platinum and they are

also less likely to polish out of the joint. In the

worst cases, the mismatch may be disguised by

rhodium plating but many workers prefer

simply to use closely matching solder in

minimum quantities.

Soldering/Welding

Index

4.4

The absence of fluxes, except for the lowest

melting point solders (where the flux is to protect

the solder, not the platinum), means that the

usual adhesiveness of flux cannot be used to

support the solder paillons in place. In practice, a

small amount of non-borate flux may be used for

this purpose, although it is not necessary

metallurgically. Alternatively, solder may be

clipped in the joint or supported by a thin

extension of stock wire that is allowed to melt

free at the last moment.

Solder Compositions

The development of solders follows similar lines

to jewellery alloys but is more complicated by the

need to meet marking regulations, match colours,

and also achieve working temperatures below the

melting point of platinum. Usually, a series of 3

to 5 solders forms a sufficient enough range of

working temperatures to enable soldered joints

to be made efficiently at different stages

of assembly.

Most platinum solders are mixtures of precious

metals, not always including platinum (but, if not,

then usually palladium) with melting ranges from

extra easy at about 950ºC., to extra hard at over

1500ºC. At the higher melting point end of the

range it is possible to accommodate more

platinum and so there is less risk of the solder

disqualifying a platinum item at the

marking stage.

Japan has a range of solders for platinum

jewellery from several grades of 999.9 fine in

total platinum group metals plus gold and/or

silver, to ones at 700 fine containing some

copper and other non-precious metals.

It is rarely economical in the long run for the

craftsman or small manufacturing jeweller to

make his own solders for platinum; several

fabricators make a more than adequate range for

jewellery purposes. It is important not only to

control the high working temperatures of the

solders accurately, but also the colour and the

relative hardness of the soldered joint. This

combination of properties is achieved by varying

proportions of platinum, palladium, gold and

silver; all precious metals that can contribute to

the normal rule that solders for 950 fine platinum

must also be 950 in precious metals total.

The deep yellow of gold quickly gives way to the

white of platinum or palladium on adding a

relatively small amount of either. For example, an

alloy of 70%/30% gold/platinum is only faintly

yellowish and increasing the platinum to 40%

produces platinum white. This applies even more

with palladium and a solder of 20 or 30%

palladium in gold is a white metal. There may be

copper and zinc in lower melting point platinum

solders as they alloy readily with platinum. As

long as they amount to less than 10%, the solder

will not discolour on heating, so retaining the

oxidation resistance which is so helpful in working

with platinum. Platinum solders at the higher end

of the range do not need fluxes.

The use of 2 to 4 precious metals and

sometimes up to 3 other metal components,

means that the total combinations are too

numerous to classify in a simple table. So, Table

4A quotes a (Hallmarking) range typical of what is

available worldwide, but there are many other

variations, particularly where marking regulations

do not specify such close control of solders.

Solders for platinum start at about 1700ºC and

drop at about 100ºC intervals down to as low as

900ºC, but very few, if any, jewellery operations

require such a full range. Most standard platinum

alloy products are soldered with platinum

containing solders at perhaps no more than two

or three stages in the higher temperature end of

the range.

Soldering/Welding

Index

4.5

Table 4A. Typical solders for platinum jewellery subject to marking

Soldering/Welding

Index

4.6Solder Nominal Working Composition Fineness FluxGrade TempºC RangeºC Approx. % Precious Metals Req.Extra Easy 945 935-955 90Ag/5Pd/5Cu/Zn 950 Tenacity No5*Easy 1020 1010-1029 45Ag/40Au/5Pt/5Pd/5Cu/Zn 950 Tenacity No5*Medium 1200 1179-1217 53Au/32Ag/15Pd 999.9 No NeedMedium Hard 1330 1319-1342 48Au/23Ag/17Pd/12Pt 999.9 No NeedHard 1435 1422-1445 65Au/30Pd/5Pt 999.9 No NeedExtra Hard 1525 1519-1533 45Au/40Pd/15Pt 999.9 No Need

*Tenacity No5 is a high temperature flux with extended life for use with extra easy solder. The residues of TenacityNo5 are virtually insoluble in water, but can be easily removed by immersion in a 10% caustic soda solutionfollowed by brushing in hot water.

Eye Protection Most soldering, and all welding operations on

platinum jewellery, involve temperatures in excess

of 1500ºC at the joint face and between 2000

and 2800ºC in the heat source. The white

radiation at these temperatures is very intensive

and the proportion of ultraviolet radiation is much

higher than for ordinary diffused daylight. This

combination presents a very real hazard to the

unprotected eye. Even a short exposure is certain

to leave an after-image on the retina that will

persist for several minutes and distort both

positioning and colour judgement. Longer

exposures will produce "arc-eye" or even

permanent damage to the retina. Choosing a

correct filter system requires a reasonable

compromise between filtering out all possible

dangerous radiation and leaving enough intensity

and colour to enable the operator to judge

position, temperature and melting in the work-

piece. Platinum sections are likely to be

lightweight, but they are melted at even higher

temperatures than steel. Grade 5/GW (Shade 5,

gas welding) filters can be used for short spells

when soldering platinum alloys but choose at

least grade 6/GW when using the highest

temperature platinum solders for long periods.

BS679 9EW, or its international equivalent

(shade 9, electric welding), to 11EW filter

glasses, should be used for long welding

exposures; grade 9 for the molten pool under the

highest temperature flame, grade 10 for TIG Arc

work. These are very dense filters which do not

allow the operator to see well enough without the

light from the heat source to position the source

and workpiece. One way round this is to use flip-

front goggles that allow a low density filter while

positioning and use safety filters which can be

brought down as soon as the work begins to

radiate. Auto-darkening filters are also available,

which change quickly between positioning mode

and welding mode. Because of the small scale

and speed of operation, it is comfortable to wear

goggles with the appropriate filters when working

with platinum jewellery alloys. Heavier jobs and

more extended spells are often better handled by

using a filter screen between the head and the

work area.

Although perhaps less dangerous to the eye itself,

the infra-red component of high-temperature

flames and arcs also needs to be guarded

against. It is unfortunately quite common to find

precision arc-welders with bright, apparent "sun-

burn" around the lower face and throat, if not

screened. This is mainly due to infra-red direct

from the heat source. While an occasional short

exposure to the skin may not be harmful in itself

(personal discomfort usually quickly reminds the

occasional operator that welding and soldering

heat sources radiate heat very directly!), repeated

or prolonged exposure is dangerous. The skin

should be covered or the head and shoulder area

screened, not just the eyes.

Warning

On no account try using even the densest

sunglasses; at the ultra-violet end of the

spectrum they may offer some protection

against general sunlight, but not against a

sharp concentrated image of an arc or

oxy-gas flame.

Soldering/Welding

Index

4.7

Finishing

Finishing and Texturing of Platinum for Jewellery

Filing

Barrel and Vibratory Polishing

Rhodium Plating

5

ManualIndex

Finishing andTexturing ofPlatinum forJewellery

Opinions differ on the difficulty of polishing

platinum, although once well polished it stays

free from tarnish virtually for ever. As with any

other metal, the polished surface of some of

the platinum alloys may scratch with heavy

every-day wear. Matt-finished platinum tends to

burnish and highly polished platinum tends to

matt a little. With reasonable protection from

knocks and abrasion, highly polished platinum

can be brilliant and kept that way. For example,

a high proportion of Japanese platinum-

palladium alloy is plated thinly with rhodium,

which scarcely alters the colour but does

impart some extra wear resistance.

Alternatively, platinum may be given one or a

combination of textured finishes ranging from a

"silky polish" to patterned or random texturing

by, in effect, greater and greater degrees of

milling of the surface. Platinum alloys respond

to polishing or texturing well; most likely it is

the wear or clogging of the polishing media or

texturing tools that gives the impression that

platinum is difficult. Minimising this effect

is the secret of good and productive

platinum finishing.

The Polishing Process

A high polish is put on most metals by removing

pits and scratches with successively finer

abrasives. The abrasive particles are much harder

than the metal and act like tiny machine tool

bits. The particles may break up, change cutting

angle, become debonded or clogged. When the

finest bonded wheel or paper mounted abrasives

have been used, the process is continued with

abrasives/polishes held in emulsified fats as

soaps, waxes, or creams applied to rotating disks

or mops. The abrasive particle size may now be

so small as to give the impression that they do

not cut/scratch, but they continue to do so on a

microscopic scale and there is a great increase in

the general friction at the interface. This heats a

thin layer of the surface that tends to flow rather

than be cut. This smears over the remaining fine

scratches and the surface presents a high lustre.

Platinum alloys differ one from another in their

“polishability” and are neither very easy nor very

difficult. Understanding the underlying process

helps towards efficient (time, quality of finish,

cost of equipment and consumables) finishing of

platinum jewellery alloys.

Because platinum does not oxidise, it is good

practice to polish individual components fully

as early as possible in the production

sequence, while there is ready access to

surfaces that may be screened after

final assembly.

There are no easy short cuts, but:

• Be very selective of the first grade of

abrasive.

• Choose the minimum first grade of

grit/compound that totally removes the

deepest defects (castings) or scratches

(wrought).

• Cut/polish across line defect such as solder

lines to minimise dragout and see just when

the defect is under control.

• Work only on the defects until the local

texture matches the bulk of the surface.

• Work more generally with finer grades of

abrasives, to remove totally scratches from

the previous grade, polishing at 90° to the

previous direction.

• Finish by buffing with a rouge type of polish.

• Prefer points, wheels, buffs, mops, that are

stiff or medium hard rather than easily

penetrated.

• Frequently renew abrasive polishing medium

or use fresh surfaces.

• There is no need to use every intermediate

grade, but sensible spacing is required.

• Do not use a file and attempt to remove the

marks with a fine emery paper - it will clog

very quickly!

Finishing

Index

5.1

Filing The favourite files for platinum are precision

Swiss watch maker's files from Vallorbe. All files

clog eventually with most metals, but these high

precision cut files appear to clog less rapidly with

platinum and respond better to cleaning than do

cheaper, less precise versions. Platinum clogs a

file in much the same way as it sticks to a saw

blade or machine tool tip (see sections on

Handworking and on Machining). Smearing is

worst where the dragging friction at the interface

is highest, as in burnishing, and least when the

tool is presented as a knife edge with a positive

rake. As wear takes place, the interface will grow

and the situation will become progressively worse,

but not as quickly as when starting with a

negative rake, as Figure 5A shows. Good filing

and most of the finer grinding operations on

platinum follow the same principle on a smaller

and smaller scale. The file should be cutting

only on its forward stroke and not dragging in

contact with platinum on the return stroke.

After minimum filing, decide whether to follow

traditional methods or a carefully selected

sequence of graded abrasives.

Traditionally, various stones, emery boards, and

abrasive loaded thread would be used depending

on access to fine detail. These have a decreasing

abrasive effect until the whole piece can be

subjected to open polishing on mops. Traditionally

named polishing media still available include

Water of Ayr stone, pumice, emery, brown or

yellow tripoli, emerald compo, ruby powder,

emerald powder, diamantine, white, green, red

and purple rouges, and also proprietary named

compounds (see Suppliers Database). Most of

these will work to some extent with platinum, but

the difficulty is prejudging the likely depth of cut,

avoiding too much penetration or too slow a rate

of finishing, and premature clogging of

the medium.

Finishing

Index

5.2The secret is to choose just sufficient cut at

each stage to remove the previous marks

before the new medium becomes clogged. This

is the reason for repeating the advice not to

remove any more platinum than is absolutely

necessary, particularly at the start of the finishing

operation. Choose the finest file, emery wheel or

paper that will just produce an even abraded

texture. Follow with a grade two or three grades

finer for the next stage, and so on. It helps to use

firm buffing wheels such as felt at the medium

polish stage and reinforced close stitched mops

for colouring/fine polishing. A typical sequence is

given in the box to the right; increase or decrease

the number of stages with practice.

Repeated practice allows operators to choose the

combination of techniques they feel happy with.

To choose a good series of grades it is helpful to

understand the various methods of grading

particle sizes and the way in which they are

“presented” to the metal.

After casting, or sawing or fine filing of only

high spots, typical finishing might include:

Fine, clean No. 4, No. 5 or No. 6 files.

Edges may be burnished with oiled tungsten

carbide burnisher.

(Tumble polishing might be inserted here for

batch products).

Sand with 240, 400 and 600 silicon grade

carbide or alumina papers.

Buff with alumina compound, then hard rouge.

Use sound techniques; avoid sloppy filing

strokes, wrong wheel speeds and cross-

transfer of abrasives.

Index

Modern abrasive systems are much more

predictable and consistent in their cutting effects.

In many cases, they are modifications of

traditional materials, often synthesised rather

than natural, but more carefully graded and

standardised than the original natural product.

A carefully controlled range of white 'compo' bars

now consist of variously calcined alumina

particles, sized and suspended in different

formulae of emulsified fats rather than the

classical tripoli. The main development has been

to 'present' the abrasive/polish in a wide variety of

geometries, some long lasting, others

consumable or renewable.

Figure 5A. The importance of having a positive rake betweenthe tool face (leading edge) and platinum. Shown here as astationary tool face leading into a rotating platinum ring as ingloss turning. The principle also holds for abrasion pointsmoving across or rotating against a stationary platinum piece.

Abrasives Grading Systems

At the coarse end, there is an internationally

accepted method for describing grinding wheels.

At the fine end there is a little less consistency

due to different methods of size ranging and the

introduction of diamond dust and diamond

compounds as polishing media. A complete

system description includes:

The abrasive compound:

• Natural or synthetic.

• Its hardness.

• Grain shape and so expected groove shape.

• Grain size.

• Friability, producing fresh surfaces.

The support medium:

• Wheel, disk, flap-wheel belt, paper, plastic

mesh, etc.

• The bond between the particles and medium.

• Optimum (linear) working speed at the

interface.

Coarse and medium grain sizes are determined

by sieve size, but national standards differ.

Particle size decreases consistently with

increasing sieve number within each standard

series, but a FEPA 240 grade may not give

precisely the same result as an ASTM 240 grade.

In choosing sanding grades for platinum, the

differences are not likely to be noticeable, but it

is best to stick to one grading system.

The finest particles are sized by sedimentation.

Again, the grading is consistent within a given

standard system, but may not be precisely

comparable across different systems. As a result,

finer grades of silicon carbide papers may be

described differently by different manufacturers

and also differ from diamond-based systems

rated in micron sizes.

Table 5A shows equivalents near enough to place

different polishing media in decreasing order of

cutting/scratch depth.

The depth of scratches produced depends not

only on the size of the abrasive particles but also

on their orientation and the depth to which they

are sunk into the backing coat on the abrasive

cloth, paper or plastic film. The most precisely

distribution coatings are produced by electrostatic

coating (Figure 5B) and this is the type preferred

for platinum alloys because the particles are

upright, remain proud of the backing and so

resist clogging better. Cloth, paper and film

abrasive surfaces appear as sheets, strips, belts,

discs, and flap brushes. A wide range of shapes

and flexibility has resulted in recent years from

suspending abrasives in a 3-dimensional web of

plastic non-woven fibres, ranging from simple

hand-pads to rotary shapes that can be very

Finishing 5.3

Table 5A. A comparison of orders of decreasing coarseness ofcut or finish based on gradings with grit or diamond sizes.

usefully adapted to jewellery making. For

instance, cylinders of such materials, loaded with

2-3 grades of alumina, are very useful for

polishing inside rings as a replacement for the

more usual flying brush (Figure 5C).

Figure 5B. Schematic diagram of the process of attracting theparticles onto the initial bond layer of an abrasivecloth/paper/film. The particles appear to remain betterorientated for work on platinum than the more traditionalcoated media does.

Figure 5C. Polishing using a hand-held machine tool.

Similarly, there are larger diameter wheels made

by a radial arrangement or spiral winding the

abrasive loaded plastic mesh followed by

controlled compaction and rebonding (Figure 5D).

Finishing

Index

5.4Standard Grades Av. Grit Diamond Grade Emery

FEPA ASTM JIS diam. (mm) (micron*) Paper GradeP60 0.25P80 0.18P100 0.13P120 0.10P150 0.08P180 0.07 IGP220 220 0.06P240 240 0.05 60P280 240 280 0.04 IMP320 0.03 45 IP360 280 320 40 IFP400 360 0.02 1/0P500 320 400 0.014P600 360 500 0.010 30 2/0P800 400 0.007 20 3/0P1000 500 600P1200 600 1200 0.004 15 4/0(1500) 1500 12(1800) 800 2000 9(3000) 2500 5(4000) 3000 4(11000) 6000 2(14000) 8000 1

1 micron (µ) = 0.001mm; 1/1000in - 25µ

FEPA: Federation of European Producers of AbrasivesASTM:American Society for Testing and MaterialJIS: Japanese Institute of Standards

Finishing

Index

5.5

Figure 5D. A selection of wheels showing the shape and surfacetexture typical of compacted plastic mesh, radial or spiralwound, loaded with abrasive in situ: (Courtesy 3M’s Scotch-Brite).

Lightweight, slightly spongy, polyvinyl acetate

wheels, carrying a carefully chosen range of

abrasives and polishing rouges, are used in Japan

for most finishing operations on platinum

jewellery (Figure 5E).

Figure 5E. Japanese polishing using a rotating polyvinyl acetate wheel.

Thirdly, there are abrasive-loaded rubber wheels

and points (Cratex type) that also work on the

basis of controlled wear continually exposing fresh

abrasive to the work face (Figure 5F). Indeed,

the working face should be dressed with a

dressing tool to clean up and reshape the

working surface. With all three types, the built-in

abrasive may be supplemented by carefully

chosen white (calcined alumina) 'compo'.

Figure 5F. Rotary brushes, flap-wheels, shaped meshes andvarious types of points may be used in many ways to producetextured/matt areas and patterns.

The recent developments appear to offer

increased efficiency in working on platinum

surfaces, mainly because they wear away under

control rather than lose their cutting ability due to

early clogging. They are likely to at least partly

replace the traditional woven fabric and felt

buffing wheels loaded with fine abrasive waxes

and rouge polishes.

The type of abrasive (corundum-calcined alumina;

chromic oxide; silicon carbide; quartzite or

crystobalite silica; cubic boron nitride; synthetic or

natural diamond) determines the hardness and

friability (which in turn determines the generation

of fresh cutting surfaces). The bond (vitrified,

resin, rubber, shellac, wax, soap) largely

determines the porosity of the structure, its heat,

wear resistance and ability to keep particles at

the designed "cutting angle". The more the bond

the less the porosity and access of coolant or

lubricant, but the stronger the wheel. Varying the

abrasive, its size distribution, the amount and

type of bond (whether waterproof, oil-proof or

flexible) and the final shape (wheel, point, disc,

paper, and paste on a carrier), creates a vast

range of grinding/polishing characteristics.

Careful choice is required to do an efficient job

on platinum jewellery alloys, varying from

soft platinum-palladium to deliberately

hardened alloys.

A dimension that is not so easily transferred from

a large scale to finishing jewellery is the speed of

rotation of wheels. What really matters is the

relative linear speed between the abrasive

particles and the platinum surface. With hand

finishing there is little scope for varying the

speed, but using rotary hand tools and bench

polishers introduces a wide speed range.

Japanese practise (Figure 5E) in the final stages

of finishing prefers a high linear speed but

achieved by using 12" (300mm) diameter cellular

PVA wheels charged with polishing compound

working at a maximum of 1600m/min for coarse

(400 mesh) buffing, to a maximum of

2000m/min for fine (1000 mesh) prior to finish

polish. This requires a speed of rotation of about

2120 rpm. For a hand rotor disc of, say, 25mm

Barrel andVibratoryPolishing

Matt or polished finishes

can be obtained by

barrelling or in a vibratory

polisher, but since

platinum production is

usually on a small scale,

the processes are not

commonly used.

Abrasive particles used in these processes are

usually chosen so that they break down

progressively in use, exposing new smaller cutting

edges, so effectively moving gradually to a higher

grade of polish than would have resulted from the

starting grade of abrasive. Platinum pieces

cannot be successfully polished in a batch

mixed with gold. Where there is an economic

batch, platinum may be first subjected to a mild

abrasive compound with ceramic chips to pad out

and disperse the abrasive medium, followed by

bright burnishing with a polishing powder and

hardened steel shapes. This imparts a burnished

finish and is more suitable for smoothly rounded

pieces than for intricate sharp cut edges that may

be rounded off to some extent.

Matt Finishing

Platinum lends itself particularly well to controlled

matt finishes ranging from a silky/satin “near

polish” to a distinctly directional brush line finish.

Polished platinum has excellent light (both colour

accuracy and brilliance) and image reflectivity

but, because of this, it also shows up lack of

uniformity in reflectivity as well. Indeed, it is

usually better to matt finish unprotected,

particularly convex, areas that are likely to be

subjected to heavy wear, than to rely on

preserving the uniformity of a high polish long

term. Polished areas juxtaposed with matt

finishes are a very useful design feature. One

may also progress to coarser but still attractive

milled, engraved or diamond-cut patterns

produced by edge tooling. Platinum's tarnish

resistance ensures that the differences between

mirror facets, polished areas and controlled matt

finishes are preserved long-term.

Figure 5G. A selection of diamond tools for producing deepertextures or faceted designs on platinum.

Finishing

Index

5.6diameter, the rpm to achieve the same linear

speed should be over 25000! This is scarcely

possible under load when the hand tool is

actually creating useful polishing friction. The

same part of the surface of the small tool would

also be in contact with the platinum many times

more frequently than for the large wheel, thus

encouraging more rapid clogging. Heat release is

more concentrated and if not controlled, will

cause the bond to plasticise and smear over the

work. There is also a far greater chance of work

snagging on wheels at high peripheral speeds

than on the large-scale slower rotating versions.

Table 5B relates when diameter, rotational speeds

and linear speeds. Note how wheel wear requires

increasingly greater rotational speed to achieve

constant linear speed.

Table 5B. The relationship between abrasive wheel diameter,revolutions per minute, and linear peripheral speed (K = 1000rpm).

Wheel Diameter Linear/Peripheral Speed (Meters/Minute)(MM) (INCH) 750 1000 1600 1800 2000 2200 2400 2600 3000

6 0.25 40K 53K10 0.4 24K 32K 51K20 0.79 12K 16K 25K 29K 32K 35K25 1.0 10K 13K 20K 23K 25K 28K 31K50 2.0 5K 6K 10K 11K 13K 14K 15K 17K 19K80 3.15 3000 4000 6400 7200 8000 8800 9600 10K 12K100 4 2400 3200 5100 5800 6400 7000 7640 8280 9550125 5 1910 2550 4070 4580 5090 5600 6110 6620 7640150 6 1590 2120 3400 3820 4250 4670 5100 5520 6370200 8 1200 1590 2550 2870 3185 3500 3820 4140 4780300 12 795 1060 1700 1910 2120 2330 2550 2760 3180

RO

TA

TI

ON

AL

SP

EE

D

Finishing

Index

5.7A necessary feature of all these finishes is to

produce them from at least one grade of finish

more polished than the grade desired. This

helps judge the uniformity and boundary of the

matt finish; it produces the desired effect in one

pass with less risk of clogging. It is considerably

more difficult to produce a good effect by

approaching from the coarser abrasive

grade finish.

Even without changing the grade of abrasive, it is

possible to produce an apparently different

texture by changing the “brushing” direction. For

instance, on an occasional craft piece, stroking a

ring shank circumferentially with a hand-pad of

Scotch-Brite product will produce a medium matt

finish, while careful stoking transversely across

the width of the ring band will give a distinctly

more matt appearance. The depth of scratches is

much the same but there is greater scatter of

incident light.

Similar differential effects can be produced with

grit blasting (mini-jet grit blasters may be used

like a fine pointed brush), steel wire wool, steel or

brass wire rotary brushes. Rotary abrasive flap

brushes and shaped meshes are the most

versatile. Highlight lines and mirror streaks can be

produced with highly polished sintered tungsten

carbide minitools. Diamond tools can also be

used, although there is a greater degree of wear

than might be expected from experience with

silver and white gold. This can be reduced by

minimising the area to be faceted and the depth

of each cut. Again, it is best to arrange these

deeper cuts and mini facets on a previously

polished or carefully matted surface rather than

attempt to use this method of decoration to save

some previous stages in the overall finishing

process. Figure 5G illustrates some of the

diamond tools for achieving these effects.

Indentation and Beaded Type Textures

Platinum responds well to coarser textures being

superimposed on either a fine brushed or a

polished finish. Hammer texturing, repoussé,

chasing, embossing (including roll embossing)

may be used, preferably on annealed platinum.

Thinner gauges may often be used, compared

with, say, silver. Chasing 26 gauge (0.46 mm)

platinum reacts much the same as chasing 22

gauge (0.71 mm) silvers. It should not be

necessary to re-anneal the platinum during such

work unless there has been repeated reversals

locally (in embossing, for instance) which may

give rise to fatigue cracking or premature tearing.

The most straight-forward way of emphasising

texture contrast is by maintaining the tooling in

as highly polished condition as possible, using

single strong blows or cuts at each point rather

than a series of overlapping applications and

starting with a high polish on the whole piece.

The high spots should remain well polished and

they, or alternatively other areas, may then be

matted with rotary brushes, abrasive mesh

shapes or points as described in the section

above. The alternative method of starting with a

matt surface and polishing the high spots after

the decoration stage requires more patience with

platinum than with most gold or silver; chased or

embossed platinum high spots do not

automatically take up a polish from the impacting

tools. On the other hand, starting with a matt

surface and deliberately matting the tools does

overcome the problem of slipping and inaccuracy

of hammering during chasing. In general,

platinum may be finished easier by burnishing

rather than by polishing.

Platinum surfaces can be decorated by

granulation, or beading back from edges with a

welding torch. In both processes, the oxidation

resistance is a great advantage, but the high

density of platinum tends to flatten the beads

more towards a drop shape rather than spheres.

It is possible to retain more bead height in

granulation by soldering than by welding, where

wetting between the whole lower half of the bead

and the surface is virtually simultaneous

with adhesion.

RhodiumPlating

Finishing

Index

5.8

Japanese platinum jewellery makers rhodium

plate the majority of their production unless there

is need to differentiate between a gold and

platinum finish in a mixed piece. The plate

imparts a greater surface hardness (about 800

HV) than for platinum alone and it also disguises

colour differences due to solder lines. It is only

effective on already well-polished surfaces and

does not cover up surface defects. The plating

can be confined to specified areas by masking

other areas (such as gold areas in mixed metal

pieces) with cellulose lacquer or chlorinated

rubber paint.

Before plating, surfaces are degreased, followed

by hot electrolytic alkaline cleaning. The

electrolyte is normally rhodium sulphate, supplied

as a concentrated solution of 100g/l of rhodium

in dilute sulphuric acid, which is further diluted

with distilled water to give a suitable

concentration, depending on the thickness of

plate required. As little as 1/2 to 1 micron (µ) is

enough to give colour and some protection; 5µ is

the maximum that should be needed for jewellery

pieces. These thicknesses may be achieved from

solutions containing 2 to 4 g/l of rhodium

immersed for 1 to 5 minutes. Glass or polythene

vats are recommended. Since the process is an

insoluble electrode process (platinum, platinised

titanium or stainless steel) the surface area is not

critical but should be run at 35°C with current

density about 10 A/ft2 (0.07 A/in2) or

0.001 A/cm2) to give about 1/2 to 1µ of plate

thickness per minute. Bath concentration should

not fall below about 90%. It is not normally

necessary to agitate the bath vigorously (this may

cause crazing) but an occasional tap to remove

bubbles which can cause pits may be useful.

Large-scale producers have a fully automated and

controlled plant, with an overhead-placing gantry.

Each operation on the multi-batch process is pre-

selected by the process controller. Typical cycle

time for a complete tray of 18 to 40 pieces would

be about 45 minutes with a total production rate

of 2000-4000 pieces a day. A typical finished

plate thickness would be about 4.5µ.

There is virtually no difference in brilliance

between a polished platinum finish and a

rhodium plated finish except for slightly more

blue/white colour with the rhodium plate. It is very

difficult to see the difference as produced, but

after 12 month's hard wear the difference may

be greater.

For unusual textures it is well worth exploring the

fusion of platinum wire clippings, platinum

powder, even carefully selected and arranged

lemels, to a platinum surface by welding or

soldering. This requires no flux and the original

surface conditions are retained without need for

extensive polishing.

It is always useful to remember that individual

components can be textured differently and

later assembled by soldering or welding without

changing the texture contrast.

Good Housekeeping

From what has been said above, it should be

apparent that the finishing of platinum pieces is

not fundamentally different from gold and silver,

but that there is a greater chance of clogging or

apparently wearing out abrasive and polishing

media. The time penalty in going back to correct

a deeper than necessary scratch or similar fault

is more significant. Every effort should be made

to avoid transferring coarser particles to

finer processes.

• Store different grades of tripoli wheels,

buffs and compo bars in separate plastic

bags or boxes.

• Keep abrasive papers flat, not face to face,

in stiff envelopes (photographic paper

packets are just about right), each reserved

for one grade only.

• Keep points, hand-pads and rotary shapes

strictly in separate plastic bags or boxes

according to grade.

• Ensure that each operative wears rough-

surfaced rubber tips on all fingers (or gloves)

and only processes one grade at a time

between washing.

• Separate grinding, buffing and final polishing

stages into separate chambers.

• Always expose platinum to fresh abrasive/

polishing media rather than risk clogging.

• Maintain working place cleanliness at a high

standard; even grease from the hand and

atmospheric dust can provide an

unintentional but effective grinding medium!

• As soon as platinum jewellery is finished, wrap

it in tissue or put it into a presentation case.

Finishing

Index

5.9

Setting

Jewellery Settings and Platinum

Setting and MountingTechniques

6

ManualIndex

JewellerySettings andPlatinum

Platinum isregarded as thebest availablematerial for gemsettings, particularlyfor diamonds, bothon the grounds ofcomplementarycolour and highstrength in thinsections such asclaws and collets.The most notablefeature of platinumis its ability to deadset, meaning that itstays very firmlywhere it is put andneither springsback nor sags.

Although white golds and platinum alloys have

improved in the last 40 years platinum jewellery

alloys still have the better combination of strength

and ductility. Modern design and fashion,

particularly where "only the best will do", has

extended platinum use not only to settings for

other white stones but to virtually all gem quality

coloured stones too. It is not surprising that in

countries where a white precious metal is

preferred, the whole piece is made up in platinum

alloy.

Design has developed to include other precious

metals alongside platinum for attractive colour

contrast reasons where marking regulations

permit; not as a cheap substitute. So, the original

good setting characteristics of platinum now

support a much wider range of designs.

Making Settings - DesignConsideration

Because of the relatively high strength and

stiffness of platinum, claws, bezels and collets of

fine section are stronger than expected on first

experience. Settings in platinum need not be

heavy unless that is a desired design

characteristic. For instance, wire no more than

0.6mm diameter is sufficient for claws to hold

stones up to a third of a carat and shaping from

1mm wire is about right around one carat.

Different grades of platinum alloy may be used in

the same piece. For instance, a setting for a

delicate stone such as an emerald may be

combined with a hardwearing shank and/or an

ornate complex cast shape; all joinable after

finishing as individual components. All of the hall-

markable platinum jewellery alloys are equally

suitable for different types of settings and the

final choice may depend on the design of the rest

of the piece.

If the designer wishes to take advantage of

the finer points of difference:

• Pt-palladium alloy is a little softer for opals,

emeralds and similar "soft" stones.

• Pt-copper alloy is better for raising grains

and pavé work. It usually gives the best

colour match with solders.

• Pt-cobalt alloy is best for complex as-cast

settings but it also retains good claw

setting capability.

• Shanks in any of the three alloys are good

for stretching up to size.

The shaping of platinum for jewellery has been

dealt with under "Handworking" and there are no

unusual problems in making settings by hand.

Ideally, the metal within the setting should be

left in a partly work- hardened state. However,

it is now possible to make or buy stamped or

precision cast settings in standard sizes, with

bearer and setting areas already partially shaped,

or more complex special shapes with remarkably

good surface finish as-cast. Even a cast setting is

worked slightly when being cleaned up, trimmed,

eased into position and burnished. With a little

preplanning, it is possible to confine the

annealing effects of soldering and welding to near

the actual joint and rely on residual work-

hardening further away for useful additional

strength in, for instance, the tips of claws. If

there is doubt about the continuing ability to work

the setting without cracking thin sections, start

with material in the annealed state. Always get

as much of the finishing to size and polishing

done before assembling the setting. Even

soldering, welding or annealing after that stage

does not oxidise the metal and it is all the

easier to finish the assembled piece, including

the settings, with a light final polishing

or burnishing.

Setting

Index

6.1

Because it is necessary to work platinum settings

with considerable firmness, it is also advisable to

mount the piece being set in a very firm

anvil/setting ball vice. Wax and shellac are both

used as the bedding material with wax being

marginally the more resilient. Warm methylated

spirits will remove residues of either without

having to disturb the potentially good prepolished

finish of the setting. A final detailed polish may

be applied with green rouge (chromic oxide),

rather than crocus, because it drags less.

Claw Settings

(Figure 6A.) The ability for platinum to provide

strong slender claws, for setting diamonds safely

but with maximum exposure, is sufficiently well

known not to need elaboration here.

Figure 6A. The claw setting is the earliest and best knownapplication of platinum in jewellery. Claws can be light insection provided there are distinct notches near the claw end tolocate the pavillion below the girdle; the "Radial Tightness" ofplatinum claws is sufficient. A typical traditional but high andopen presentation of a solitaire diamond.

Platinum has been used successfully in all of the

classical claw type settings for single stone rings,

two to five stone straight or waveform settings

with scallop, arcade, scroll, organ-pipe styles or

decorations. It is certainly not limited to setting

diamonds. The common feature to most claw

settings using platinum is that stones can be

supported on thinner bezels, narrower bearers

and with fewer slender claws than with most

other hall-markable precious metal alloys. Most

users of platinum prefer to start with material

as near to finished shape and size as possible,

to minimise the amount of platinum scrap. This

immediately emphasizes the advantage of

precision casting the settings or even the whole

piece. When working on a group of stones, the

close setting possible with platinum dictates that

you work from the centre progressively outwards.

Claws are levered first against the centre stone

until they are all spaced evenly around the girdle,

using the surrounding material as the "purchase"

for twisting/levering the setting tool. The process

is then repeated on the next outer position and

so on. This is particularly important with pavé

settings (no prongs) in order not to run out of

beadable material around the centre stone.

Figure 6B. Claw settings.

Pavé

An important application of platinum is in making

the settings for pavé work (setting diamonds or

other small stones close together, similar to

cobblestones). In some respects this may be

viewed as a development of the classical cluster

setting whereby a group of stones, not

necessarily all the same size, are set in a shallow

domed circle. In pavé work, (Figure 6C) a small

plate, shallow dome or even a hemisphere of

platinum can be drilled out until the holes are

almost touching, but there can still be enough

Figure 6C. Pavé setting. (A) A typical hole drilling plan for aclose-packed hexagonal arrangement for 5-10 point diamonds;(B) All holes are first drilled parallel sided; (C) Top bearers arethen made by countersinking; (D) Similar opening out of thepavillion; (E) Adjacent almost radial cuts provide a tongue toform a bead over the edge of the girdle which is cleaned upwith a grain tool; (F) Each stone is held by three beads.

Setting

Index

6.2

strong metal remaining in the network to retain

closely set stones at their girdles and show little

more than the raised bead. In this case, fully

annealed material should be used to avoid the

difficulty of hard spots in unannealed alloy

making the raising of beads or close fine

setting difficult, thus outweighing the

advantage of increased metal strength. Of

course there is no point in reducing the thickness

of the platinum to such an extent that the culets

of the stones make uncomfortable contact with

the wearer. Normally the pavé platform is raised

on the ring shank or brooch surround with a

gallery or basket back similar to those used for

cluster rings. Pavé and similar close display

settings are normally prepared by drilling recesses

in small sections of sheet or cleaning up recesses

in precision cast components and then producing

an accurate seating with a precision burr or

fraise. As with any other setting material, it is

important to match the stones beforehand so

that it is not necessary to produce too much

variation in seating sizes with the burrs. Only in

mass production is wear of drills and burrs likely

to be a problem.

Figure 6D. Pavé setting.

Channel Setting

Platinum is very good for making channel settings

for much the same reason as pavé; baguette

stones can be adequately supported by strong

but narrow edge bands, leaving the end girdles of

the stones touching apparently unsupported in

the centre of the channel. In practice, the sides

of the channel will be cross-braced with spacers,

particularly if handmade, but platinum does not

normally need cross-spacers below every pair of

Figure 6E. Channel settings. (A) to (c) handmade channel ringfor square or baguette stones with inside edges cut to formbearers from two flat rings and with spacers which must clearthe stones so they lie end to end (d) to (e) shows cast channelsection with (f) cast-in bearing which needs finishing with anonglette graver (use flatter 15¡ cutting edge than normal forgold at 30¡to 40¡) to seat the girdle just below the rim of thechannel (F), before turning the edge back over the stones (h)with a setting tool.

touching girdles. Cast channels may not need

many, if any, cross-spacers and the beginnings of

the bearer recess may be cast into the inner

upper edge of a standard channel. This reduces

the amount of graver work needed to complete

the bearer and of course reduces the weight of

the ring (Figure 6E). The bearer is deepened

sideways into the channel edge with an onglette

graver, the baguettes are 'snapped' in and the

thin top edge of the channel is forced over just

above the girdle of the stone.

Figure 6F. Channel settings.

Invisible Setting

Platinum readily supports the principle of pavé

and channel settings in that the continuity of the

stones from one to another is emphasized

without drawing too much attention to the setting

itself because it is strong but slender. It is

possible to arrange the stones in such a way that

no platinum is visible between them (Figure 6G).

This is done by cutting special grooves or inset

slots in the gemstones just below the girdle.

These receive very carefully prepared claws which

allow the stones to touch at the girdles above.

Either the crown facets, or total internal reflection

Setting

Index

6.3

Figure 6G. Principles of invisible settings. (A) to (C): Triangular,square/rectangular, hexagonal stones are best for closepacking: (D) Six-rayed star-cut stone in plan and elevation; (E)Double French or Cardinal cut similarly showing the position ofhidden grooves in all or alternate facets below the girdle intowhich pre-set prongs spring to hold the pattern in place.

in the case of diamonds and some simulants,

hide from view the small penetration into the

pavillion. This type of arrangement obviously

depends on strong claws with some springiness

and they must still be small to be well hidden.

Platinum is ideal for this application.

Figure 6H. Invisible settings.

Unusual Settings

The high mechanical properties of platinum and

the fact that it does not soften or relax with time

(except at high temperatures) has led to its use

in some innovative types of settings. The basis of

most of these is that the stress created by

elastically deforming platinum is predictable and

can be relied upon to grip a stone without

relaxation. By combining engineering stress

calculations with a good knowledge of what

stresses some gemstones will safely withstand,

it is possible to support the stones more

openly than would be possible using

conventional settings. In effect the stone is

clipped in a gap cut into a prestressed ring of

platinum. The gap is slightly less than the

diameter across the girdle of the stone and when

clipped into simple curved notch seatings in the

open ends of the ring, the stone is held firmly by

elastic hoop stress. The stone appears to be

suspended in space (Figure 6I). A similar principle

may be used to hold the stone in a "split

tube" setting.

Figure 6I. A “tension” ring setting.

Figure 6J. Tension settings.

Setting

Index

6.4

Setting andMountingTechniques

It is good practice with platinum to:

• Drill at a slow speed.

• Start holes with a pilot drill and then use a

drill size smaller than the stone to finish.

• Use sharp drills, resharpening often.

• Lubricate with beeswax or methyl salicylate

(oil of wintergreen) frequently.

• If the drill breaks, dissolve out with 30%

sulphuric acid.

• Use a new or well-cleaned burr only as

much as necessary to finish the seating.

• Keep millgrain wheels and burnishers

meticulously clean and reserved only for

platinum.

Opinions differ as to the best tools for setting

platinum against stones. It helps to have a matt

texture, to get an accurate positioning without

slipping in the initial stages of moving platinum

onto the girdle of the stone. On the other hand,

the finishing of the beading and the tidying up of

the surrounding setting is best done with a highly

polished burnisher. Platinum burnishes well, but it

also drags easily in contact with the slightest

trace of debris.

Transfer of debris from tools is avoided by

repeated retouching of the high polish on the tool

face after every few strokes. This is not as

arduous as it sounds if the initial polish on the

tool face is good. While a 4/0's emery finish is

good enough on a burnisher for gold, it is

advisable to use something better for platinum.

One classical method is to use putty powder

mixed with methylated spirits, spread on a

smooth piece of hardwood as the touch-up

polisher. Methyl salicylate (oil of wintergreen) in a

piece of sponge also acts as a good quick

lubricant for the next series of strokes after each

tool repolishing. For only occasional use,

hardened tool steel scorpers may be used for

platinum setting, provided the working face is

highly polished, though tungsten carbide tools

take and retain the best polish and should

therefore be used for repeated work on platinum

settings. In particular, the cutting edge of a

tungsten carbide scorper gives the sharpest and

neatest cut.

Setter's Wrist!

Advice on firmness of support, sharpness of tools,

lubrication, leverage, and as-cast setting

surfaces, is given in the interests of good quality

platinum settings, but there is another aspect.

The occasional worker in platinum often

complains that "platinum is hard on the wrists"!

Typical platinum settings do offer more resistance

than, say, 18 carat yellow gold, but this is the

reason for its success as an apparently slender

but strong setting for the stones. There is usually

no need to "move" as much platinum about in

cutting a seating, making a bead over a girdle, or

setting a claw, as would be the case with softer

alloys. Use short cutting strokes and frequent

lubrication; lever claws and material for beads

into place and maintain all tools in top condition.

Above all, cultivate a policy of "right first time",

with careful preplanning of each part of the

setting operation. Much of the frustration with

platinum comes from having to rework your, or

someone elses, previous errors, usually on now

work-hardened material, and having to remove

defects in otherwise well-polished areas!

Setting

Index

6.5

Combination

Combinations with Platinum

7

ManualIndex

Combinationswith Platinum

Platinum jewelleryalloys are attractiveand versatilecomponents incombination withother preciousmetals, particularlywith regard tomixed colours and textures.

Combination

Index

7.1There is no technical reason why platinum should

not be used in combination with other white

metals, especially when using its very good

settings capability. However, it is unusual for

platinum to be combined with silver, because of

the low colour contrast and large difference in the

inherent costs of platinum and silver. In some

countries, marking regulations dictate that the

combined piece is described as silver unless the

two metals can be separately distinguished. This

would seriously undervalue the piece. The

inherent values of platinum and 18 carat white

golds are more comparable, so there is less

deterrent to combining it with platinum,

particularly when taking advantage of the high

strength of platinum in light sections, delicate

settings and filigree work.

The most popular examples of platinum

combinations employ white platinum jewellery

alloys in contrast with one or more coloured golds

(Figure 7A). There are also ample opportunities to

vary texture. With its high melting point, good hot

strength, and freedom from oxidation, platinum

lends itself very well indeed to forming

components (even finished polished) and then

using soldering, fusion, welding, cold welding,

mechanical joining or even adhesives to

assemble the combined piece. There are very

many combinations of alloy and methods of

joining possible and this section of the manual

simply suggests various strategies rather than

trying to be an exhaustive catalogue.

Figure 7A Platinum/gold combination jewellery.

Assembling, Decorating, or Co-Working?

There are basically three routes to making

combination jewellery. For occasional one-off

pieces, the jeweller may combine components

each made as far as possible in a different alloy.

This is assembly. Combining a platinum setting at

the shoulders of a gold ring shank is a familiar

example. Alternatively, he may finish the bulk of

the piece in one alloy and add another of

different colour and/or texture. This is decoration.

Gold may be decorated with platinum and vice

versa by inlaying techniques, surface mounting,

differential etching or plating. There may be no

clear distinction between assembly and

heavy decoration.

Some simpler designs lend themselves to batch

production or a common design at an early stage

in the production sequence. For these, it is often

possible to devise a combination nearer the raw

material stage.

Examples of combination nearer the

semi-fabricated stage include:

• Bar of alternating layers of two or

more alloys.

• Sheet made from different alloy strips.

• Tube with different alloys concentrically

layered.

• Simple platinum shapes distributed regularly

or irregularly within a matrix of gold.

• Simple gold shapes distributed regularly or

irregularly in a platinum matrix.

These combinations may then be further co-

worked, or selectively cut, to form jewellery

components with some control over the resulting

pattern, but the basic arrangement is decided by

the initial combination pattern.

Combination

Index

7.2The remainder of this section gives examples of

ways in which platinum combination jewellery can

be produced, with the emphasis on the principles

and design planning, rather than on pattern

details. It should be apparent that platinum

is a very versatile precious metal for

combination jewellery.

Assembling Mixed Alloys by Co-casting with Platinum

The high melting point, relatively good hot

strength and excellent oxidation resistance of

platinum jewellery alloys are an excellent basis for

co-casting solid platinum with an alternative

molten alloy. Probably the commonest example of

this in the past has been to precision cast a gem

setting in platinum, prepolish it and then attach it

to a wax ring shank pattern.

This is then re-invested and the new wax melted.

The platinum setting is left in place such that it

welds solid to liquid when another jewellery alloy

such as 14, 18, or even 22 carat gold is

injected. Many combinations are possible, giving

a versatile style of design for combination

jewellery where marking regulations allow. If co-

casting is intended from the start, it is best to

make the platinum settings with dovetailed or

similar shoulder protrusions, to aid wax

attachment and liquid/solid co-cast welding.

(Figure 7B) outlines the method.

An extension of this method is to link together,

not weld or solder, platinum swivels, chain-links

or precast components, join them into the ends

of wax patterns, burn out and then co-cast with

another liquid jewellery alloy. The linked platinum

components are unaffected by the process and

can still swivel or slide on each other, but are

firmly joined to the other precious metal

components. This allows chains, bracelets and

similar structures to be produced already joined;

indeed, with the swivels already polished. Where

several links need to be made in one cast, it is

best to arrange them radially from a common

feeder from the tree base, rather than in-line.

Assembling Mixed Alloys byWelding and Soldering

The earlier section covering soldering/welding,

shows that platinum responds well to both; no

new principles are introduced by joining platinum

in these ways to other precious metals. The

general rule is to use platinum techniques when

joining platinum to fine gold (and normally,

22 carat gold) and carat gold joining techniques

when joining to 14, or more usually, 18 carat

golds. In the former case no fluxes are needed,

but operating temperatures are over 1,000°C. For

carat golds, temperatures below 1,000°C are

sufficient, particularly when soldering. A flux

appropriate to the carat gold or solder is used.

Combination welding and soldering

summary:

• Combinations of platinum and fine gold

require no flux.

• Joining is a relatively simple process;

if the shape is already a good fit.

• When inlaying platinum with 18 carat

golds, use gold solder flux; 18 carat gold

can oxidise.

• For surface decoration rather than inlaid,

use yellow gold solder and flux; they melt at

lower temperatures than platinum solders

and are easier to match with yellow gold

at edges.

Figure 7B. A precision cast platinum setting (A) can be co-castwith, say, gold. It helps to have small projections at theshoulder to locate the wax pattern for the ring shank. afterreinvesting, melting out the wax and casting with gold, theliquid gold/solid platinum interface makes a sound weld.

Combination

Index

7.3Co-Working

Several simple arrangements of platinum with

yellow golds can be made early in the working

process, so that the basic arrangement survives

subsequent working operations, to form a built-in

pattern. This may either be for stock or

customised, depending on the size of batch. The

most common example is alternate strips of

platinum and one or more coloured golds side by

side in sheet or strip form. Coupons cut from

such stock can be cross-rolled to broaden the

stripes, but normally further rolling is longitudinal,

in which case the stripes remain constant in

width and are elongated in proportion to the

reduction in thickness. Similarly, platinum shapes

may be arranged in a pattern in a mould and gold

cast around them. The original shapes completely

weld to the gold matrix and the resulting slab

may then be co-worked. The slab rolls down as

though it were a homogeneous solid, so the

shape will be elongated in the direction of rolling.

The plan shape can be controlled quite accurately

by cross-rolling or rolling at an angle, but the

amount may be limited by roll width and so

requires careful planning. The principle is shown

in Figure 7C, for platinum discs in a gold matrix,

but other simple shapes would behave in a

similar fashion. Gold discs in a platinum matrix

behave in the same way, although they are more

likely to be incorporated by inserting solid gold

discs in holes in platinum strip and co-rolling,

rather than by co-casting (which is, nevertheless,

quite possible).

Design using composite stock is likely to follow

the lines of "what manipulation process can I use

to re-arrange the composite pattern into an

interesting jewellery shape". In other words, the

design will be relatively simple. Some designers

have combined a good knowledge of rheology

(plastic deformation of solids, including mixed

metals) with a flair for original design.

Nevertheless, most original combination pieces of

jewellery are created by decoration and/or

assembly rather than co-working.

Inlay Or Intarsia Work

Originally, intarsia work referred to mosaic work

and in principle this can be done by inlaying

platinum shapes into gold or vice versa. In

creating some simple combination patterns, it is

possible to cut out, or better still, punch out,

shapes from platinum and fill the space with the

corresponding shape punched out of, say, 18

carat gold. The platinum shapes will then fit into

the gold spaces. Start with, 10 to 20% thicker

gauge flat and annealed material than the finally

required gauge. Following carat gold techniques

rather than platinum, small paillons should be

placed at intervals along the interface and the

parts soldered together from the intended

front side.

Figure 7C. Representation of the predictability of shapechanges when rolling a coupon of platinum discs in a gold matrix.

Finish the composite sheet by giving it a few light

passes through the rolling mill (Figure 7D). 18

carat gold solder melted into the holes of a drilled

platinum shank is an interesting design

alternative; the advantage being that the solder

melts easily into place (Figure 7E).

Figure 7D. Platinum/gold combination sheet.

Combination

Index

7.4One of the most popular and versatile decoration

techniques is to inlay wire sections into

cuts/grooves, milled, sawn or chased into the

other precious metal surface either previously

polished or prematted under control. Ideally, the

section of the groove should be wider at the

bottom than at the top (Figure 7F). This may be

done by making two or three cuts; the first main

cut follows the drawn out design with a square

graver (vertical sides) and this is followed up with

a fine graver, slanted so that it does not touch

the opposite upper lip, but so that it undercuts

slightly one side, and then the other side, of the

base of the first cut. The wire to be inlaid should

have a diameter about half the depth of the cut

and is set by hammering with a flat faced punch

so that it remains slightly above the surface of

the background when the groove is filled. A flat

graver may be used to trim away the extra inlaid

metal, or it may be ground down and the joint

surface polished or matted in the usual way.

Figure 7E. 18 carat gold solder and platinum ring.

Platinum wire let into 18 carat gold requires little

more than tamping into the groove, flatting and

polishing or matting. Platinum receiving fine gold

wire inlay may not need very much undercutting

because the platinum lip is usually strong

compared with the very malleable fine gold. The

filling requires little force and the two metals will

virtually cold weld.

For slightly more spread out lines, or bands, the

gold wire is first tacked into the start of the

groove, with a flame raising the temperature of

the wire just to melting point. The wire is then led

and simultaneously eased into the grooved

pattern, following along with the flame until the

groove has been filled. If the correct gauge

(usually between 0.25 and 0.75mm gauge) is

chosen, the gold should just stand proud of the

groove and simply needs flatting down and

polishing flush to finish.

Figure 7F. Inlay of a gold motif in platinum. the undercutting of the channel is exaggerated for clarity. In practice, platinumwould not need much of a lip to retain the gold.

Wider gold shapes in platinum can be created by

chasing the outline of the shape into the

platinum and fusing gold wire into the shallow

recess until it is just proud of the surroundings.

Where the area to be filled is larger still, it is

better to cut the gold from thin sheet to fill the

recess, and make up any small gaps with fine

wire filler.

Filigree Platinum

Platinum wire section (not necessarily only round

wire) is strong, even in thin sections, particularly

if used in the half-hard or even harder condition.

It is particularly effective in suspending other

precious metals or precious stones in a brooch

frame, or from a bangle, bracelet or necklace.

One neat way of making an end join or

suspension is to take the half-hard wire, say 0.15

to 0.45mm diameter, fuse one end into a tiny

sphere, thread the free wire through a hole in the

other metal, say 18 carat yellow gold, tension it

and then secure the free end by soldering to the

gold surround (Figure 7G). Alternatively, the

platinum wire can be given a head (and finally a

tail-end) by fusing on a small piece of fine gold of

predetermined weight. No flux is needed and the

fine gold fuses into a small sphere of predictable

diameter. This enables you to make fine gold

nodes or connection points at the ends or

meeting points of platinum filigree wires, to form

Combination

Index

7.5

Figure 7G. Filigree platinum. a diamond “ball” supported byplatinum strings in a gold frame. Two ways of finishing ends areshown. the frame should be pressed inwards while making theends, then allowed to spring back to tension the wire.

single suspensions, spider webs, networks and

meshes. Once the predetermined weight of fine

gold is tacked or twisted over the connection

point, it may be fused without flux by carefully

heating the junction just over the melting point of

gold (i.e. just over 1063°C). If the junction is

really overheated, the molten gold will dissolve

the platinum wire!

Wire Sections Combination

Manipulating wire sections by twisting, plaiting

single or multiple strands, twisting several strands

on a core, twisting or cross-linking chains and coil

weaving, are ancient techniques for making

jewellery. One of the easiest ways of exploring

platinum combination design and techniques is to

combine platinum and other precious metal wire

sections (not necessarily only round sections) by

twisting or plaiting (Figure 7H). This may be

followed by soldering (assembly) or by rolling or

forging (co-working) that will probably also cause

cold welding. Introducing platinum in this way

raises no fundamental problems, but the

following hints may help head off minor problems.

Figure 7H. Combining metals by twisting or plaiting

• Check the marking regulations in the

intended market; while touching wire

sections may each be markable, co-worked

sections may not be individually

distinguishable.

• Start with the platinum and the other

metal(s) equally soft to avoid the softer

twisting more than the harder.

• Choose annealing temperatures to suit the

other precious metal, but allow a longer

time for platinum to recover/stress relieve, if

not fully annealed.

• In making a ring/bracelet band, match the

wire ends to be joined at a diameter the

same as, or smaller than, finally required, or:

• Solder all the wire ends into a cross-piece to

disguise the mismatch.

• It is simpler to expand a band to size than

to cut back to size and attempt to rematch

the wire ends.

Engraved/Etched Patterns

A simple arrangement with good design potential

for platinum/gold combinations is to laminate

platinum with one of the carat golds or plate it

with 22 carat or fine gold. Fine line or broader

pattern shapes may then be produced by either

engraving or etching through the gold surface to

expose the bulk platinum beneath, which may

subsequently be matted rather than polished.

An etchant that attacks gold but will stop acting,

or slow down greatly, on reaching platinum is:

16% Hydrochloric acid,

8% Nitric acid,

1% Iron perchlorate,

75% Water.

Stop-out varnish, liquid asphaltum, hard ground,

and plating resist, all suitable for gold surfaces,

are normally suitable for protecting the retained

gold part of the design on platinum during

etching. However, once the platinum is exposed,

the gold does tend to etch away sideways more

rapidly than downwards. So, to retain (platinum)

lines in fine outline, it is advisable to stop etching

as soon as the fine lines have 'developed'.

Polishing Combination Pieces

Having gone to the trouble to make an effective

design by combining platinum with another metal

of different colour/texture, it is usual to try to

preserve the boundaries between the

components as precisely as possible. With a little

pre-planning and careful polishing it is possible to

minimise both the smearing of the softer metal

over the harder and the creation of a step

between the two. This is easier where the

boundary is simple, rather than convoluted, and

the operator has some control over the local

direction of polishing.

Figure 7I. Platinum /gold combination jewellery.

It is helpful to:

• Choose finishing techniques more

appropriate to platinum than the other

metal, even when platinum is in the

minority.

• Prefer a sharp cutting technique to a smear

polishing or burnishing technique throughout

finishing.

• Note that diamond paste polishing

techniques work on the basis that diamond

is so hard that it treats all precious metals

as equally "soft", so differential polishing is

minimised.

• Polish along the boundary rather than

across, particularly in the final polishing

stage. With intricate designs this may mean

using miniature rotary tools.

ConclusionAny combination design has to be carefully

considered from the point of view of

minimising mixed scrap. While clean, single

precious metal alloy scrap can usually be

remelted or joined economically, this is not

usually so for combined alloys which often

have to be recycled through an early stage

refining process. It is not surprising,

therefore, that combinations of platinum

with other precious metals are rarely made

for stock but rather to special order. Large

producers of platinum combination jewellery

tend to make up their own combination

semi-finished stock. They are skilled in

choosing economic routes, semis product

sizes and designs that are a good

compromise between versatile designs in

finished products that will sell well and

minimise precious metal scrap losses,

including the cost of slow moving inventory.

Combination

Index

7.6

Stamping

Introduction

Tool Materials

Blanking/Punching

Closed-Die Forming

Summary

8

ManualIndex

Introduction

For the purposes ofthis section of themanual, stampingmeans all thoseprocesses usingpunches and/ordies in a hand -operated fly-pressor a mechanicalsingle or doubleacting press. Thisincludes blankingand punching, bothof which involveshearing, anoperation similar tocoining andembossing, thatshapes or imprintsa slug of metalbetween closed die.

Figure 8A sketches a sequence of operations

used to form a ring blank, so avoiding extensive

machining. Stamping might be extended to

include stretch-forming and deep-drawing of

sheet and forming of wire, into chain links, for

instance. Platinum responds well to stamping

operations, as is shown by some of the coin and

medal minted products seen around the world, as

well as some of the product seen in Figure 8B.

However, it is advisable to choose tool and die

materials along with tool clearances carefully, to

obtain the best tool life and dimensional

accuracies in the components. The amount of

power needed to work platinum is greater than

for gold and silver and thus tool hardnesses

should be correspondingly higher also.

Figure 8A. Sequence of operations for forming a ring band from thick strip.

Tool Materials Except for the unusual case of continuous mass

production of platinum components such as in

chain making, there is no need to use exotic tool

materials. It is more economic to use standard

air-hardening chromium tool steels for both

cutting edges in blanking/punching and for

closed dies. These are popular general purpose

tool steels capable of air hardening, as opposed

to oil-quenching, because of their molybdenum

content. As a result, they are less prone to

distortion and dimensional change in heat-

treatment and have good wear resistance. The

principal reasons for choosing this type of tool

steel are its good heat-treatability, good

machinability in shaping the tools and moderate

toughness, with medium cost for medium runs on

light to medium stock. This would be the case for

most platinum jewellery batches.

A high-carbon high-chromium tool steel might

be chosen for continuous light working

operations such as simple bending, because of

its superior hardness and increased wear

resistance. It would be more prone to distortion

and cracking in heavier coining operations.

A typical tool composition would be:

%C 0.95-1.05 Heat treat tools to

%Mn 1.00 max 58-60 Rc (720-760HV)

%Si 0.50 max by air quenching at

%Cr 4.75-5.50 940-970°C and tempering

%Ni 0.30 max at 250-450°C (near flat

%Mo 0.90-1.40 response with tempering

%V 0.15-0.50 temperature)

Stamping

Index

8.1

Blanking/Punching

Closed-DieForming

Stamping

Index

8.2There is an optimum clearance between punch

and die which will produce a blank showing a

minimum amount of bending and with the edges

as smooth as possible. This varies from one

metal to another, being least for metals of high

ductility. The general rule for blanking and

punching platinum is that the clearance

between the punch outer diameter and the

internal diameter of the blank holder should be

3-4% of the stock thickness.

Since there is usually no need to anneal

between cutting the blank and its further

shaping, it is usual to start with annealed

material. However, some subsequent operations

work better with half-hard stock and it is not

difficult to blank from stock at a hardness of 85-

100Hv. Die wear is increased in cutting harder

material and if die life has to be maximised, the

platinum alloy should be used in the annealed

condition (for likely hardnesses, see Table 1B).

The clearest example of closed- die forming is the

minting of coins and medals, but the principle

extends to the stamping of components for

making up into "catalogue" jewellery with more or

less embossing on the surface. Coining demands

the highest pressures within closed dies, due to

the requirement for intricate surface designs and

the need for accurate, repeatable blank volumes.

These conditions demand a rigid and accurately

aligned machine frame and accurately matched

and unyielding dies. Most other stamping

operations on platinum are less demanding, but

in all cases, dies must be polished and well

maintained to minimise die wear.

Simple shapes such as leaves, petals and hearts,

may be blanked and shaped in one operation and

subsequently welded (possibly laser welded)

together in a variety of arrangements. Similarly,

findings such as simple settings for calibrated

precious stones, earring parts and brooch

components may be made this way (Figure 8B).

Forming chain links from tape or wire is a special

case of closed - die (continuous) forming. In such

cases, more specialised die materials or die

inserts, and processes such as plating, may be

used to extend the life of dies between recutting.

In long coining runs, the dies are usually

polished, chromium plated, and re-polished

periodically by specialists. The press operator can

also increase the overall life by occasionally

stress-relieving the whole die or the die inserts for

a few hours at 200 to 250°C.

Figure 8B. Stamped pieces.

There are no special problems in stamping

smaller batches of platinum using closed-die

tooling, except perhaps that the dies wear

slightly quicker than they would on gold alloys.

Summary The variety of operations that might be included

under the heading of "stamping" are wide, but

few jewellery manufacturers are likely to use

stamping machinery for long runs on platinum

production alone. Alternating between platinum

production and other precious metals does not

introduce any major problems; most platinum

jewellery alloys are amenable to precision

stamping. However, platinum alloys usually

require more force/power than working with, say,

18 carat gold and, so, in long runs, there is a

need for more robust dies and machinery. Dies

should be maintained more frequently in order to

continue to benefit from the inherently good

workability of platinum. Good housekeeping is, as

always with platinum, cost effective. For instance,

tools and dies used for various precious metals

must be cleaned before and after use on

platinum. Platinum readily picks up and retains

(often by effectively cold welding) other metals.

Such local contamination could even cause an

assay sample to fail, but is more likely to have an

adverse effect on the good working properties of

platinum, particularly after heat-treating, soldering

or welding. The good housekeeping details

given in the sections on soldering, welding

and handworking, apply to stamping

operations also.

Finally, stampings are most likely to be made

from wrought stock of consistent uniform

analysis, so the scrap represents a valuable

resource well worth segregating into a separate

batch identified by a single batch number and

not mixed in with miscellaneous scrap, lemels

or sweepings.

When stamping platinum:

• Keep all tooling clean.

• Do not use excess lubrication.

• Keep press surface and dies highly polished.

• Clean plates of beeswax, other lubricants,

and metal particles that could damage a

high finish.

• There is a tendency to smear or drag wear

on working tools.

• Keeping a high tool polish minimises wear.

Stamping

Index

8.3

Machining

Introduction

Technical Background

Processes

Parting Off

Machine Facetting

Gloss Turning

Heat Generation

Materials

Tools Setting

9

ManualIndex

Introduction

The average jobbingjeweller is muchmore likely to usehandworkingtechniques,including small-scale machining inthe form of sawing,drilling, filing, andtexturing, than afully equippedmachine shopwhere machinabilityof platinum needsto be optimised.The advice forhandworking was toorganise the designand assembly tominimise theamount of metal removal.

Most batch producers will explore fully the

workability of platinum before resorting to

extensive machining. For instance, as was

outlined in the stamping section (Figure 8A), ring

blanks may be made by manipulating washers

from thick sheet and forming the outer band

shape either by stamping or by ring rolling.

Parting from tube would be an intermediate

method that introduces cutting one stage earlier.

Bending a precut length of rolled D-section

around a mandrel or triblet and welding the join is

the method most commonly used by the craft

jeweller. Gloss turning would then be the first

surface machining process in any of these routes

and the saving in terms of metal removal

compared with machining from the solid is

significant (Figure 9A).

Platinum sticks to most forms of tooling and

cutting edges and it may remove some of the

cutting tool material when it breaks away. This

gives the impression that platinum is inherently

difficult to machine or that it is an unusually hard

material. In fact, platinum is not unusually

demanding in terms of work done in machining,

provided the correct tool settings and

lubrication conditions are maintained. But,

frustration is easily caused by ignoring the need

to frequently re-prepare cutting edges or use

continuously exposed fresh cutting surfaces.

Under such circumstances, the jobbing jeweller is

likely to consider using machining methods, or

sub-contracting work to a machinist, particularly

when making large items of jewellery or plate, or

in preparing batches of similar components.

Figure 9A. Typical dimensioned sequence (A) to (C) of creatinga wedding band blank from a washer punched from strip. Inthis case the cross-section is changed about its centroid at aconstant radius (C=9mm) from the axis. if the same end shapewere to be drilled machined from a solid right cylinder (D) Itwould require almost 66% metal removed as swarf. Note: Thisis not a fair estimation of the savings in scrap (by the stampingroute) because cutting the washer from strip creates “solidscrap” too but this is usually more useful than swarf.

There is then a need at least to understand the

techniques that a subcontractor is likely to use,

particularly to optimise design and production

economy, and also to minimise process scrap.

TechnicalBackground

Machining any metal by lathe or shaper/planer

(ie. with a single tool face) involves a significant

force opposite to the effective direction of cutting

and with the work required dependent on the

volume and speed of cutting. This work

overcomes friction at the interface, shears the

metal and mostly appears as heat. This in turn

raises the temperature of both the metal

remaining and of the swarf removed. Lubrication

helps to reduce the friction and also to conduct

some of the heat away.

The same principles apply in multiple tool cutting

processes. In effect, band saws and slitting and

grinding abrasive wheels are multiple tool cutting

processes, but the points at which the work is

done and heat is generated are separate from

each other and come into action in a cyclic

fashion.

The main problem in machining platinum is its

tendency to cold weld to clean tool faces, teeth

and edges. If allowed to build up, this alters the

tool setting, lubrication, interface geometry and

temperature conditions, leading to clogging and

the stick/slip wear of tooling. Platinum also has a

low thermal diffusivity, which means that more of

the heat generated remains near the

tool/platinum interface than would be the case for

gold. This increases the interface temperature

and "cold welding", which in turn leads to the

removal of minute tool particles.

Machining

Index

9.1

Optimising the machining of platinum depends

on minimising friction by correct tool settings

and reducing and removing heat as efficiently

as possible with lubrication. Alternatively, it

may be possible to use tooling that is

specifically designed to break away cleanly,

thus constantly replenishing the

cutting surface.

The principle forces involved in lathe turning

(including gloss turning) the shaper/planer and

even boring and drilling, are similar. In lathe

turning, the tool remains stationary and the work

rotates; in shaping, the work is clamped and the

tool moves over it, but the relative movement and

force vector set up are essentially the same. They

are shown in Figure 9B, which illustrates the

principle forces and tool angles that have to be

considered to maximise machinability of platinum

by minimizing the cutting force and protecting the

cutting edge as long as possible. The

arrangement shown is for the shaper/planer, but

the principles extend to an external lathe cut,

where the work surface would be convex, and to

drilling/boring, where the work surface is normally

concave in relation to the tool tip. The most

important force contributing to the work is Fc, the

cutting force opposite to the direction of cutting.

Anything that can be done to reduce Fc will

reduce the total work done and heat

generated. Anything which increases Fc is likely

to increase friction, tool wear, distortion of the

interface and vibration.

What we need to do is to reduce the redundant

work more than the essential cutting work. This

requires careful choice of cutting speeds, cutting

depth, and cutting interface angles. Increasing

speed and/or depth of cut increases the force,

the rate of metal removal and the rate of heat

generated, but not necessarily the rate at which

the heat is removed. Altering the angle of the tool

face to the work, mainly alters the area of the

interface as wear takes place, the ease with

which lubricant gets to the working edge and

consequently the rate of heat removal. It also

changes the way in which swarf is generated and

cleared from the interface.

The forces, particularly Fc, but also friction,

and the heat generated:

Increase with

• Cutting speed.

• Depth of cut.

• Hardness of the metal.

Decrease with

• More lubrication.

• Optimum tool angles.

• ‘Sharp’ cutting edge.

Figure 9B. The tool/workpiece interface, showing the shearplane of the chip and the two main forces acting on the tool.

Processes Parting Off

It is common practice to part off tube into ring

blanks prior to gloss turning on a lathe. With

platinum, this can lead to rapid tool wear and

give rise to large burrs, too much kerf and poor

edge surface finish. So, it is better to slit the

platinum using thin alumina or silicon carbide

resin bonded discs. These can be as little as

0.3mm thick, provided they are run in disc guides

to avoid excessive flexing. Depending on the

diameter (the maximum safe speed decreases

with diameter) the effective surface speed may

be between 1300 and 3800 M/min. The surface

finish of the cut surfaces is determined by the

grade of abrasive used in the disc and may be

about 2 microns (µ) for a disc of 400 grade grit.

Machining

Index

9.2

A burr is produced on the inner surface of the

tube/band when finally slitting through. This is

minimised by a fast feed rate, particularly just

before break through, but this increases the rate

of disc wear. A compromise is to feed forward at

20 to 30mm/min at a disc peripheral speed of

about 1400 M/min, and to cool with water or

water soluble coolant/lubricant to prevent burning

the disc. Where there is sufficient demand to

justify taking all steps to increase quality and

productivity, it is also useful for the tube itself

to be rotated counter to the spin of the

slitting disc.

Machine Facetting

Platinum bands may be facetted using the same

type of machines as used for facetting gold

bands. These machines “scallop” tiny pieces of

metal away in a geometrically planned pattern

using a rotating disc with a lapped diamond on its

circumference. The only difference is in the likely

life between regrinds of the diamond cutting

edge. Whereas an average facet design might be

repeated on 100 or more gold bands before

regrinding the diamond, with platinum, the

number of repeats would be about 8-10. As the

depth of cut is also less, so each platinum ring

takes about 4 times as long to facet as a similar

design on 18 carat gold. It is possible to make

deep facet cuts on platinum, but this shortens

the life between diamond regrinds even more

drastically. A new or reground tool can be used

initially on either gold or platinum, but once it has

been used to facet platinum it should not be

used on gold; it will not give the expected high

finish, because of minute damage to the

diamond cutting edge.

This apparently expensive process should be seen

in perspective. The initial investment in diamond

tooling is no different, whether for gold or silver

(assuming the operator is facetting both gold and

platinum), so it is the regrind costs that have to

be compared. With careful process control

(shallow cuts, accurate setting, low rotor speed

with plenty of no-load time between cuts) tools

should last, say, 8 completed rings before a light

lapping is needed to restore an acceptable finish

ability. The costs compare well with skills costs for

hand-finishing a high bullion value ring.

It is possible to adapt the machine facetting

process to produce a prefinal polish state for a

plain band as a substitute for machine gloss

turning. The facetting machine is programmed to

make very small shallow cuts all over the top

surface of an accurately profiled and sized

platinum ring blank. This produces a highly

reflective finish automatically, but one which is

not absolutely smooth. If a smooth finish is

required, the final stage should be hand polishing

rather than a gloss-turning machine. The

difference is that the myriads of facets are

produced by the diamond moving quickly but

intermittently over the stationary ring surface,

while gloss turning rotates the ring continuously

beneath a single diamond point; there is no off-

load cycle time for heat to dissipate.

Gloss Turning

The most important small scale batch jewellery

machining operation is the gloss turning of

wedding bands, which requires more care when

employed on platinum than on yellow gold. The

standard jeweller's lathe tool for gloss turning gold

has a relatively obtuse cutting edge, with 15°

negative top rake and a narrow glossing flat

immediately below this edge. This is intended to

burnish after the cutting edge, but it also

interferes with lubrication between tool and

workpiece (Figure 9C). With platinum, a tool with

a more positive top rake lowers the cutting force.

However, tool wear is slower, lubricant access is

improved and deterioration in work surface finish,

although not burnished, is only very slight. This

tool tip arrangement is less robust than the

conventional negative top rake, but with the

mainly shallow cuts for glossing this is not a

problem. The effective machining speed in gloss

turning is a combination of the rotational speed

of the mandrel/ring blank and the speed of

traverse of the tool over the width of the band

(which will often be radiused).

Machining

Index

9.3

A high rpm combined with a slow traverse will

produce the finest grooves tightly packed.

Provided the tools are correctly set, sharp and

clean, this will give the best direct gloss effect

with platinum.

Figure 9C. Diamond glossing tool geometries.

However, a high rotational speed with worn tools

increases the rate of heat development,

decreases the specific heat removal capacity of

the lubricant and causes the wear problems to

rapidly escalate.

With platinum, gloss turning is best carried out

in two stages. Firstly, the surface is prepared

with a ceramic tool to remove all but the finest

blemishes, and then secondly, a diamond tool

produces the final gloss finish using only 2.5 to

3 micron cut depth.

Heat Generation

The rate at which heat is generated will depend

principally on the linear cutting speed, whilst the

rise in temperature will depend on the thermal

diffusivity of the tooling, the workpiece and the

lubricant. Doubling the surface speed from, say,

50M/min to lOOM/min will roughly double the

load, other things being equal, but it is unlikely to

increase the heat removal rate in compensation.

Gloss turning - Summary:

• Start with fully annealed material.

• Use a tool with 5° top rake and 5-7° front

face clearance.

• A rigid lathe set-up is essential to minimise

"chatter".

• Adjust surface speed to 70-110M/min.

• Make very light cuts 0.0025-0.005mm

deep.

• Use a slow traverse rate across the

band face.

• Use flush lubrication to remove heat

and swarf.

• The preferred gloss tooling material is single

crystal diamond.

Materials The order of increasing tool life is roughly:

• Tool steel.

• Cobalt bonded tungsten carbide tip.

• Glass bonded (polycrystalline) alumina

(sapphire).

• Cubic boron nitride.

• Sapphire.

• Diamond.

• Polycrystalline diamond compact.

Tools

All common tool materials will cut platinum; a

problem only arises when tool life is important, as

in extended gloss turning or repeated batch or

jobbing operations. Where tool life is a

consideration, tool steel and tungsten carbide do

not have as long lives as they do with gold or

silver and so more advanced materials should be

used. On the other hand, some large users take

the view that the bullion value of platinum

products is high enough to justify rough

machining first with tungsten tooling, to get as

good a finish as possible for a few pieces, and to

then discard the tool and finish with only a light

demand on more expensive tooling which has

Machining

Index

9.4

been kept in very good condition. The order of

the materials in producing increasing quality of

surface finish may be much the same, on the

grounds that surface finish depends on preserving

a clean cutting edge, free from significant wear.

However, there may be exceptions, as when

polycrystalline tools begin to wear they may

expose fresh cutting surfaces, which, with

platinum, helps continued sharp cutting. This will

usually spread the cutting edge and a broader cut

will often result in a poorer finish. To date, the

best combination of wear resistance and gloss

finish has resulted from finishing with a single

crystal diamond tool. It also helps to spend time

in setting up the tooling correctly and then to use

it on a run of all the same standard sized ring

blanks, rather than to change settings (with

inevitable slight inaccuracies) between different

sized blanks.

For consistent work on other than occasional

pieces it is necessary to use diamond. Both

single crystal and synthetic polycrystal diamond

have been used. Even so, the durability of the

diamond tool will be lower with platinum than

with other jewellery metals. Diamond is the

hardest material available, but diamond cutters

are well aware that even the abrasion resistance

hardness of diamond varies with different faces

and directions. Where a single crystal

diamond is used, it helps to orient the stone

so that the front face of the tool is a (100)

crystallographic plane.

Lubricants

Most machining fluids reduce tool loading

considerably compared with dry running; their

effectiveness to do so depends largely on their

viscosity and, in turn, their ability to remain at the

tool/work interface. However, different machining

fluids act in different ways. A cutting fluid is

designed to assist swarf and heat removal from

the cutting edge, while others of a more viscous

(thicker oil or gelatinous) nature tend to lift the

tool a little and so enhance the burnishing action

of the tool. The latter is better for gloss turning

for instance, while the former is more efficient in

precision cutting. Some fluids are compounded to

emphasize heat removal ability.

Traditional lubricants for slow speed or hand-

working of platinum include oil of wintergreen

(methyl salicylate) and 10% (by weight) gelatin in

water. Neither were developed specifically as long

lasting fine turning or gloss turning lubricants; and

neither contain inhibitors, so they can cause

corrosion or mould on the machine tool

components (not on the platinum!). Whilst they

do appear to have about the right sort of viscosity

and penetrability into the cutting face at low

speeds for maximum tool life, some of the

commercial cutting fluids are preferable. These

do contain inhibitors, so machine tools are better

protected and their dynamic viscosity and heat

scrubbing capacity can be better suited to

penetrating and staying at the difficult tool

platinum interface during high speed turning.

Machining

Index

9.5

Tools Setting The rake angle (ß) determines whether the tool

will remove metal in a ribbon or continuous chips

or whether it will plough a furrow instead of

cleanly removing metal. To cut rather than plough

requires a larger rake angle for a soft metal, such

as annealed platinum, than for a relatively harder

metal, such as steel. But, the practicable angle

also has to allow for the fact that the tool will

wear too quickly or even crumble if the angle is

too large. Some metals can be machined to a

better surface finish with a negative rake angle

which may also introduce a greater degree of

burnishing.The clearance angle affects the ability

to pass lubricant over the working interface and

the likelihood that the friction interface at the

back of the tool cutting edge will increase

significantly with only a little tool wear.

However, the clearance angle cannot be

decreased too much before the tool tip becomes

too fragile to maintain a firm stance and avoid

vibration. For platinum, avoiding interface friction

is of a higher priority than tool bulk, so rake angle

is always towards the positive side and the

clearance angle above average.

Typical setting should be:

• Rake angle (ß)=0 to 10°.

• Clearance angle =5 to 10°.

• Prefer annealed, to work hardened

platinum alloy.

• Depth of cut <0.05mm (0.005mm

preferred).

• Slow cutting speed <50M/min.

• Use good cutting fluid liberally.

Machining 9.6

Index

Lasers

Lasers and Platinum Jewellery

Laser Systems

Why Platinum Responds Well

Some Design Principles

Safety Considerations

10

ManualIndex

Lasers andPlatinumJewellery

Laser Systems There are four main classes of industrial lasers

according to power rating; further sub-divided into

continuous wave (cw) and pulsed lasers. The

effectiveness of all lasers depends on the

absorption, reflection and reaction properties of

the target material.

Continuous wave lasers are typically used for

marking, scribing and soldering. Where energy is

absorbed, the material is heated and may be

melted, vaporized from the surface or (photo-)

chemically changed, usually oxidized, so that

there is interference in normal viewing light or a

colour change. The marking pattern is achieved

by using a mask, or by driving a focused spot very

precisely on x and y co-ordinates on CAD-CAM

principles.

Pulsed lasers are more typically used for welding,

surface modification and cutting where they

provide relatively high pulse energies but with

limitations on the pulse repetition rate. Most

industrial lasers are Class 4 systems requiring

safety precautions but most jewellery lasers are

Class 1 and have built in safety devices.

Lasers for Jewellery

Laser machines used for jewellery are relatively

low powered and usually designed at the highest

level of safety: Class 1. They are compact,

moveable on casters, and arranged so that the

operator sits at the machine, see Figure 10B.

Figure 10B. Typical laser machine used for jewellery operations.Courtesy Baasel Lasertech UK Ltd, Daventry, UK.

Lasers

Index

10.1Introduction

Laser machines have become increasingly

popular in the last ten years in relation to

jewellery. They can be used for official precision

marking in an assay office, marking out patterns

during design development or as a batch

production decorative finish technique. Machines

are well developed now for various joining

techniques, including welding and brazing. Those

same machines may further justify their initial

cost by their versatility in upgrading castings and

repairing components. On a mass production

basis, dedicated machines are used for making

chain. Platinum alloys respond well in all these

applications.

Principles of lasers

The term Laser is an acronym for Light

Amplification by the Stimulated Emission of

Radiation that produces a sharply focused light

beam that melts, burns or vaporizes most

materials. The laser beam is generated in a

cylindrical crystal with mirror polished ends by

applying intensive light pulses from a special flash

generator. The crystal likely to be used in a

jewellery laser is synthetic Yttrium Aluminium

Garnet (YAG) doped with neodymium. About 10%

of the energy can be taken off by making one of

the end reflectors only 90% reflecting. The result

is a brilliant beam of monochromatic coherent

radiation that is highly directional and may be

very accurately focused. The principle is sketched

in Figure 10A.

Figure 10A. Diagram of the main components of a lasergenerator. (Baasel Lasertech UK Ltd)

A typical laser machine can weld almost all

metals and alloys quickly, reliably and precisely

but the efficiency does depend very much on the

properties of the target materials. Components to

be joined, or upgraded in the case of castings,

are arranged under visual control or jigged, and

exposed to one or more laser pulses. A typical

pulse lasts 2 to 10 milliseconds, (ms). The device

is equipped with a stereomicroscope and a cross

hair to facilitate the exact positioning of the parts

and to target the exact position on the work piece

where the laser pulse will strike. The height and

lateral position of the work piece can be adjusted

slightly within the field of the stereomicroscope.

One of the characteristics of a good jewellery

laser machine is the effective depth of focus of

the beam. The beam in the working zone is

shaped by a multi-element lens at the exit of the

laser generator. Normally, a machine used only

for marking needs little depth of focus as long as

the marking field is in a plane normal to the

beam so the optics are arranged to give a flat

field. The laser welder is easier to use if the

beam in the working zone is cylindrical because

the spot diameter does not change over several

millimeters of focus; see Figure 10C. As with a

macro camera lens, the depth of focus increases

with increasing working distance from the exit

lens to the work piece, the standoff distance.

Figure 10C. Laser beam shapes.

The total welding energy can be controlled by

adjusting the intensity of individual laser pulses,

pulse length and pulse frequency. Pulse to pulse

energy stability is also important so that

satisfactory settings for a particular job remain

consistent. Some machines can be pre-

programmed by storing different combinations of

settings that have been found satisfactory for

particular jobs. Suitable adjustments for various

materials can be made through trial and error but

certain heat flow principles allow good predictions

of suitable welding parameters. The overall speed

of the process is largely controlled by the time

taken to position the work for each pulse. Pulsing

normally takes place in still air but some cooling

is possible by directing an air or inert gas jet into

the work zone. Weld quality for reactive alloys can

be improved by using inert gas shielding but this

is largely unnecessary for platinum alloys. Any

vapour produced can be extracted from the work

chamber via an exhauster unit. Some machines

allow integrated control of the laser pulsing and

air/gas flow by using a pedal switch with two

operating pressures and single or sequenced

pulsing is decided by the length of time of the

pressure on the pedal. This leaves both hands

free to position the work. Each pulse is only a

small part of the total energy dissipated within

the laser generator itself, so this is cooled

effectively by a heat exchanger with an external

cooling water supply.

Table 10A. Typical Parameters For Jewellery Laser WeldingMachines.

The very high heat intensity laser beam pulse

generates a surface temperature well above the

melting point of platinum at a very small diameter

target spot. This allows the user to weld, under

ideal conditions, as close as 0.2 mm from

complicated and heat-sensitive component parts

such as hinges, catches, fasteners, settings,

most precious stones, and even, with care, pearls

and organic materials. Provided the heat flow

Lasers

Index

10.2

Approx Machine Size Range 700-1350 x 250-550Ht x width x depth, mm x 650-860Weight, kg 85-150Input Power supply 115 or 200-240V/

50-60Hz single phaseMax average operating power 30-80W #Focal spot diameter 0.2-2.0 mmPulse energy 0.05-80 J (Watt.sec)Peak pulse power 4.5-10 kWPulse duration 0.5-20 msPulse frequency Single to10 HzPulse energizing voltage* 200-400V# average light bulb power but because all in-phase,equivalent to an order of magnitude more.* Voltage used to trigger Xenon flash, which, in turn,affects the energy of the laser beam output

SW Performance -Why is a good beam quality so important?

Good beamquality

Bad beamquality

FocalArea

Misalignment of workpiece in beamdirection due tomanual positioning Spot diameter

remains nearlyconstant

Spot diameter changes dramatically

Figure 10D. Effect of varying laser controls on the cross section of the heat affected zone.

Lasers

Index

10.3Alloy Composition Pulse Energizing Pulse Length Comments

Voltage* MillisecondsPlatinum - all 200-300 1.5-10 Very good welding resultsGold - 999 fine 300-400 10-20 Darken target area; high power necessaryGold - 18ct yellow 250-300 2.5-10 Good welding resultsGold - 18ct white 250-280 1.7-5.0 Very good welding resultsSilver - 925/835 300-400 7.0-20 Darken target area; high power necessaryTitanium 200-300 2.0-4.0 Inert gas cover recommendedStainless Steel 200-300 2.0-15 Inert gas cover recommended

Table 10B. Typical Laser Welding Parameters For DifferentJewellery Materials.

away from the target is limited, it is possible to

retain heat-treated or cold-worked hardness in

most jewellery alloys; this works particularly well

with platinum jewellery alloys.

The parameters shown in Table 10B are based on

an average beam diameter of about 0.5mm on

the materials stated and may need adjustment

for other compositions. The three main control

parameters have slightly different effects on a

single material as shown in Figure 10D. Different

materials can have very different thermal

diffusivity properties, melting temperatures and

latent heats of melting. The way these important

physical properties combine together have a

marked effect on the energy intensity needed to

produce an effective weld. Welding is achieved

only with adequate heat being absorbed through

the surface, not when the beam is reflected off

the surface. The colour and reflectivity of the

surface is very important. Where there is a

combination of high reflectivity and high heat

dispersion (e.g. silver and high carat golds), it is

helpful to mark and darken the target spot or line

with a dark blue or black felt tip pen or

permanent marker. This effectively increases the

absorption coefficient of the surface.

0.2mm. beam diam., 2.5 ms pulse, incr. volts300V 350V 400V

2.5 ms pulse, 300V., incr. beam diam.0.25 2.5 4.5mm

0.2mm. beam diam., 300V., incr. pulse2.5ms 10ms 20ms

A B

C A Increasing voltage, increasespenetration.

B Extending pulse increasestotal pulse energy and radialheat flow.

C Greater beam diam., withconstant pulse energy givesheat spread rather thanpenetration.

Why PlatinumResponds Well

The efficiency of a laser welder differs from alloy

to alloy. The same set of control parameters will

result in the same power delivered in each

welding pulse but the melting effect of each pulse

depends on the proportion of the heat energy

absorbed through the surface rather than

reflected, and then on:

• Specific heat from room temperature to the

melting point

• Melting point (liquidus)

• Latent heat of melting

• Thermal diffusivity

While the melting points for most platinum

jewellery alloys are very high, their thermal

diffusivities are all similar and relatively low (table

10C) so the laser is able to deliver enough energy

to melt a very small focused spot at each pulse

but with only a small heat affected zone. With the

possible exception of palladium (lower melting

point at 1555°C) all the platinum group jewellery

alloys respond to the laser machine settings in a

very similar way. There are slight differences in

surface colour when melting in air (the copper

and cobalt alloys tend to be a little grayer, for

instance) but these differences have little effect

on the optimum control settings. On the other

hand, gold and silver alloys have much lower

melting points but five to seven times higher

capacity to transmit heat away from the target.

With platinum, the laser target can approach very

close to delicate stones and normally it is

unnecessary to remove stones before making

repairs, for instance. A skilled operator can

achieve welds with little or no scarring and in

most cases components should be near finish

polished before welding. Alternatively,

Metal/Alloy Melting Thermal. point °C diffusivity

999 Platinum 1773 0.245990 Platinum 1773 0.2455% Copper 1745 0.2885% Cobalt 1765 0.2233% Co/7%Pd 1740 0.2295%Co/10%Pd 1730 0.2205% Iridium 1795 0.24510% Iridium 1800 0.24215% Iridium 1820 0.24120% Iridium 1830 0.237Palladium 1555 0.2405% Palladium 1765 0.24710% Palladium 1755 0.24715% Palladium 1750 0.2475% Rhodium 1820 0.2505% Ruthenium 1795 0.2555% Tungsten 1845 0.267Fine Gold 1063 1.200Fine Silver 962 1.702

Table 10C. Melting point and thermal diffusivity for platinum alloys.

components can be tack welded together,

adjusted until positioned correctly and the final

welds can be made with laser settings that

improve the cosmetic finish of the tack welds.

While almost all platinum jewellery alloys fall into

this easily managed category, it is worthwhile

studying how to make minor variations in laser

settings to achieve optimum conditions for each

specific alloy.

Another feature of the localized heating effect of

the laser is that dissimilar alloys can be joined

more readily than when using more bulk melting

processes. There are still some incompatible pairs

but the laser welder can produce narrow weld

zones so that the change in colour or texture

between the two components is sharper and

better delineated.

Lasers

Index

10.4

Some DesignPrinciples

The most obvious common feature of a typical

range of laser welded platinum jewellery is that

remarkably small sections, thin stampings, low

gauge wire can be at least stitch welded with

precision. Welds that are more extensive and

repairs of casting defects (see later section) are

made by a series of overlapping pulses.

The laser is limited to joints that can be hit by the

direct beam, so, deep and undercut sites should

be avoided.

Figure 10E. Platinum and gold pendant where design andproduction take advantage of laser welding.

The essential points of the design in Figure 10E.

are that cold drawn square wire is used (with the

main stress on the diagonals) and several of the

components are elastically stressed so that they

give a sense of springiness and rigidity. The tightly

localised and limited heat diffusivity allows springy

and hard components to be joined with little or

no softening. This enables designs that make

good use of lightweight springy sections or robust

fasteners. The very limited heat affected zones

also allow joining of more dissimilar alloys (assay

rules allowing) than would be possible with large

scale melting. In good commercial practice, it

would be advisable to bring all the components in

Figure 10E to a higher degree of finish prior to

joining. Most of the high finish is preserved and it

is easier to clean up and polish separate

components than the finished piece.

The laser welder can also be used to make joints

in other ways. With careful control it is possible to

effectively spot weld through one light section to

another beneath but unlike normal spot welding

this does involve melting through the top layer.

Two or three thin components can be sandwich-

joined by, in effect, a laser version of riveting; see

Figure 10F.

Figure 10F. Simple "rivet-type" joining techniques.

Upgrading and Repairs

Some platinum jewellery manufacturers producing

pieces based on castings may feel that the initial

capital cost of a laser welder around $40,000 to

$50,000 is uneconomic. In practice there are

probably as many laser welders used for

upgrading castings as there are for making

welded pieces so it is not so difficult to justify a

dual-purpose arrangement. In addition, laser

machines on low power can do a useful job in

cleaning up and assembling wax patterns prior to

investment. Do not leave any wax residues

around when welding platinum alloys; it can

easily cause carbon contamination.

Ideally, platinum alloy jewellery castings should

meet a consistently satisfactory standard of

soundness. Some small surface defects can be

repaired at the fettling stage but small pinhole

defects sometimes only show up late during

polishing. The expense to both the finisher and

caster of returning such components for recasting

is often avoidable by using the laser welder to

upgrade the castings. This applies particularly

when the casting and finishing operations are on

the same site.

There are several techniques. A simple glossing of

a small area of rough surface texture may be

achieved by using a rapid repeat sequence of

pulses with the laser beam set relatively wide and

shallow. Small pinhole defects (around 0.25mm)

can be filled by similarly pulsing around the edge

Lasers

Index

10.5Drill hole to same diam.as platinum rivet wirethrou’ both thicknesses.

Fuse one end of rivetwire to small bead.

Thread rivet wire thro’both plates.

Laser weld slight rivetprotrusion to shape.

Platinum components can be laser rivetted by a variety of techiques,two of which are illustrated above.

Preformed hinges can be spot-welded or rivetted into place withprecision and without damage.

Rivets, in effect dowels, can be hidden by laser, thro’ the surface, to the rivet end receased beneath.

Staggering the rivets or spotwelds helps give lateral stability.

Drill hole to samediam. as platinum rivetwire but not thro’ back.

Only tack weld neededto back plate.

Thread thro’ top plate.

Laser weld slight rivetprotrusion to shape.

Rod end drilled1mm; spring wirewelded in with filter

Half hard 18ct gold,spring-bow, laser welded

Pair of hard drawnPt arcs laser welded

2 arcs free to vibrate

of the defect. Larger defects can be effectively

filled with fine filler wire touched into the defect

and, in effect, cut to size with the laser beam

striking the wire and then leveling the filler down

to the original surface. The colour of the filler can

usually be matched accurately to that of the

casting. The principles of the laser machine when

used for upgrading castings and when welding are

virtually identical so virtually all of the advice in

the sections above still applies. In particular the

same safety principles apply.

SafetyConsiderations

There is an IEC standard for Radiation Safety of

Laser Products, including equipment

classification, requirements and a user's guide.

The objects of the standard are to:

• protect persons from laser radiation in the

wavelength range 200nm to 1µm by

indicating safe working levels laser radiation

and by introducing a system of classification

of lasers and laser products according to

their degree of hazard.

• require both the manufacturer and the user

to supply information and establish

procedures so that proper precautions can

be adopted.

• ensure adequate warning to individuals of

hazards associated with accessible radiation

from laser products, by way of signs, labels

and instructions.

• reduce the possibility of injury by minimizing

unnecessary accessible radiation, give

improved control of the radiation through

protective features and provide safe usage

of laser products by specifying user control

measures.

The IEC standard, ref 2, defines four general laser

classes; but virtually all jewellery lasers are Class

1, with a pulse peak power of considerably less

than 1MW and are inherently safe or made safe

by engineering design. Most of the necessary

safety features are not only built in but the

machine cannot normally be operated unless the

necessary safety features are automatically

triggered, making them Class 1 lasers. Jewellery

lasers should fulfill the requirements that apply to

a Class 1 laser device for the absolute safety of

the operator and anyone else in the vicinity (i.e. it

has successfully passed official safety standards)

This should also ensure adequate eye protection.

Typical safety devices include:

• The laser will not operate until the operator has

put both arms through the hand openings and

activated both interlock switches. The

positioning of the interlock switches also

encourages safe and steady holding of the

work piece in the correct working position and

the arms safely block radiation escaping the

work zone.

• The best working position is determined by

using the microscope and this viewing field

automatically restricts the position to the

controlled zone. Apart from direct safety, it

greatly helps to prevent back and neck ache if

the seating to the microscope is adjusted so

that the body is always upright and relaxed and

the operator is calm and concentrating,

particularly when triggering laser pulses.

• The operator's eyes are protected against direct

laser radiation (and some of the secondary

radiation) by special shutters that close

momentarily over the view as the laser pulse is

triggered. This happens so quickly that the

operator does not normally notice the

disappearance of view.

Lasers

Index

10.6

• The laser beam generates secondary radiation,

including infrared and ultraviolet light, from

most materials. This can be observed through

the laser protective (filter) window without

damaging the eyes but visible secondary

radiation can cause headaches if the eyes are

directly exposed to it for any length of time.

The laser beam itself remains invisible.

• To ensure unhindered observation of the

process, the laser protective window is

otherwise completely transparent. A halogen

lamp illuminates the work in the operating zone

even when welding is taking place.

The only voluntary danger is to the unprotected

hands of the operator who could inadvertently

place part of a hand under the pulsing laser

beam and suffer local burns to the hands or

fingers. At the power of most jewellery welding

lasers, one or two pulses on the fingers may be

experienced (like needle jabs) without more than

short-term discomfort. Multiple pulses,

particularly at the same spot can produce a small

but potentially deep burn and this merits medical

attention to ensure no infection results. Only

under very unfavourable circumstances will the

secondary/scattered radiation reach an intensity

significant enough to burn the skin of the hands.

Normal exposure of the skin to low levels of

scattered radiation at the wavelength of 1064nm

can be regarded as physiologically safe. The

infrared laser radiation acts like normal heat

radiation.

Repeated laser pulsing of relatively high thermal

diffusivity materials can easily cause normal

heating of the component to a temperature that

can burn the fingers. Jewellery (rings, watches,

bracelets) should not be worn inside the work

zone as they may be struck by the laser beam

and even if they are not damaged they can

conduct heat to the fingers. A rapidly heated ring

is very difficult to remove from the finger in the

confines of a laser cabinet! In addition, jewellery

items can reflect or even focus the scattered

radiation and thus cause minor skin burns.

References/recommendations forfurther reading.

1. Utilization of lasers in the joining of gold and

platinum for jewelry, Costantino Volpe &

Richard D. Lanam, Proc. Sante Fe

Symposium on Jewelry Manufacturing

Technology, 1998.

2. Laser Machine Safety Standard. BS/EN60825

(IEC 825-1)

Lasers

Index

10.7

Glossary

Glossary

Comparative Weights and Measures

11

ManualIndex

Glossary

Definition of termsin italics and cross-references.

AcceleratorSpeeds setting of investments,

mainly for economic production

reasons. Based on strongly

crystalline substances such as

common salt, sodium citrate,

Rochelle salts. Platinum

investments are more likely to

need a retardant to allow time

for de-airing etc.

See also: De-airing, Gypsum-based, Retarder

Air-HardeningAn alloy construction or tool

steel capable of delaying

hardening after heating so that

there is time for cooling

(quenching) in air rather than

oil or water. Reduces cooling

stresses.

See also: Quenching

AnnealingSoftening work-hardened

metals by heating to a suitable

temperature (approximately

half the m.pt in °K) to cause

recrystallisation. For most

platinum alloys 1000°C is a

typical annealing temperature;

lower for heavily cold-worked

alloys.

See also: Cold-worked, Hot-worked, Work-harden

Arc-eyePainful, temporary, gritty

sensation apparent round the

eyeball overexposed to

intensive radiation from a

welding arc or high

temperature flame. Usually

seems worst at night after the

overexposure; lasts up to a day

or two; prevented by correct

goggles.

See also: Ultra-violet radiation, White radiation

BaguetteA relatively modern style of

stone cutting producing long

rectangular gemstones with

parallel facets.

Beading BackDecoration of a surface near

an edge by fusing the metal

locally and allowing it to ball

up and retreat with and over

the remaining edge.

See also: Granulation

Bezel SettingA bezel or box setting used for

cabochons and simple step cut

stones. Made by wrapping a

thin strip around the girdle, cut

to length and joined (off a

corner), stood on edge and

further joined to a base that

supports the stone.

See also: Claw (prong) setting, Millegrain

BurnisherUsed mainly as a short-

handled setting tool to

lever/wipe metal over the edge

of a stone and achieve a semi-

polish effect by surface

working.

See also: Scorper, Onglette graver

CaratUnit of weight for precious

stones: 1 carat = 100 points

= 0.2 gram. Also measure of

fineness of precious metals:

24 carat = 100% (pure), so

e.g. 18ct = 18/24 = 75%

precious metal content.

Carat PlatinumAn informal term applicable to

some platinum alloys in the

USA where platinum (as

distinct from platinum group

metals) may be present in

various proportions between

50% & 100% to match typical

carat gold proportions.

See also: Final assay,Fineness, Negative Tolerance

CarborundumSilicon carbide, SiC. hardness

9.5 on Mohs scale, made by

fusing sand and coke in an

electric furnace, grinding and

grading. Very brittle and best

adapted to grinding materials

"softer" than steel. SiC also

used as high-conductivity

refractory.

See also: Corundum, Emery,Wet and dry paper

Glossary

Index

11.1

CastabilityThe ability of an alloy to be

melted, poured into a mould,

retain sufficient fluidity, take up

an accurate detailed

impression of the mould cavity

and be extracted without

cracking. Difficult to quantify in

a single simple test.

See also: Chilling factor, Fluidity, Lost-wax casting

Casting GrainMetals, or more usually alloys,

prepared for melting and

subsequently casting, by

dividing charge material into

small gravel sizes by pouring

melt into water to form shot or

grains. Scrap offcuts may be

turned into grain for easier

remelting.

See also: Induction melting, Lost-wax casting

Casting TemperatureTemperature at which power is

switched off, coil lowered and

spin arm started up in

investment casting. Platinum

alloy casting temperature

usually 2000°C or over so

casting usually triggered by a

direct pyrometer signal in mv.

See also: Emissivity, Induction melting, Superheat

Chasing Hammering of a design on the

face of an article with a tiny

punch or moulding in relief by

working directly on the surface

with a chasing hammer. The

piece is usually supported on a

yielding surface such as wax or

pitch.

See also: Cold-working, Embossing

Chilling FactorCooling capacity of a mould

calculated from volume

specific heat of the mould

material and the mould/melt

temperature difference. Value

for plaster, low; silica, medium;

cold copper, very high.

See also: Casting temperature, Superheat, Thermal diffusivity

Claw (Prong) SettingPrecision cast or fabricated

from wire/strip with slots to grip

the girdle or tips folded over

girdle of a stone seated in a

bezel or collett.

See also: Bezel setting, Millegrain

CoiningA stamping process where the

volume of the closed die

impression is the same as the

blank; imparts a sharp

impression with no flash at the

parting line; often a final

operation after stamping a

rough shaped blank.

See also: Pressing, Cold-worked, Work-harden

Cold-WorkedReduced in section by rolling,

forging, drawing, or worked by

bending or even embossing,

sufficiently below annealing

temperature to cause strain-

hardening. With annealing

temperature about 1000°C., Pt

"cold works" at low red heat!

See also: Annealing, Hot-worked, Springiness

CollettSmall horizontal parallel sided

ring or with a conical taper to

form a seat for the pavilion of

the stone.

See also: Bezel setting, Claw (prong) setting

Compo (sition) BarsConsumable bars applied to

load polished wheels, buffs,

etc., made from finely ground

oxides bound with wax or soap;

the colour indicates the likely

oxide and cutting power.

See also: Jewellers rouge

CorundumAlumina, A1203, (NOT

Carborundum) used both as a

refractory and, in very finely

ground (gamma phase) form,

as an abrasive/polishing

compound.

See also: Carborundum, Emery, Refractory

Glossary

Index

11.2

Coupon (RectangularBlank)A miniature sheet of metal of a

convenient (postage stamp to

visiting card) size for jewellery,

cut from conventional sheet or

strip. Lends itself to angle or

cross-rolling and various hand-

working operations.

See also: Semis

Crown (Facets)The upper parts of a facetted

gemstone above the girdle,

including the table; facets are

usually cut to maximise the

light gathering ability of highly

transparent stones and/or

maximise multiple reflections

from both clear and deeply

coloured stones.

See also: Pavilion, Baguette

CrystobaliteThe highest temperature phase

of silica, stable and with high

strength retention from

1470°C to the m.pt., 1700°C.

See also: Invest(ment), Refractory, SIlica

CuletThe small facet at the base of

the pavilion of a (usually)

brilliant cut stone parallel to

the table. Mainly to prevent

splintering but often omitted

from modern stones.

See also: Pavilion, Crown

De-AiringRemoval of bubbles from a

slurry/cream/paste of mixed

and setting investment to avoid

bubble defects on the final

castings. Assisted by vibration

and or vacuum. Easiest before

investing the mould but

desirable after investment too.

See also: Invest(ment), Lost-wax casting, Retarder

Deep-DrawingA sheet pressing operation in

which the punch pushes the

sheet through a die and cause

the rim of the sheet to be

drawn in radially under

controlled pressure, so

allowing relatively deep shapes

to be formed. Can be used to

start tube forming.

See also: Pressing, Stretch-forming, Work-harden

DiamantinePolishing powder made from

calcined alumina, NOT

diamond dust.

See also: Jewellers rouge

DomingHammering sheet or a circle

with a spherical ended punch

down into a matching

hemispherical hollow in a block

to form a domed depression.

After trimming, two matching

domes may be soldered to

form a hollow sphere. Platinum

alloys respond well.

See also: Cold-worked, Embossing, Spinning

Ductile (Ductility)Capable of being drawn

(usually cold) into wire or tube

without fracture; usually

measured by % elongation and

% reduction in area in a tensile

test.

See also: Annealing, Cold-worked, Malleable

EmbossingSimilar to, often combined with

chasing. Specifically, raising

patterns in relief up from the

surface (like the boss of a

shield) by hammering/punching

from the obverse side. Doming

is a special case of embossing

with a lot of radial drawing in.

See also: Chasing, Cold-worked, Doming

Emerald PowderPolishing composition made

from finely ground green

chromic oxide, NOT Beryl.

See also: Jewellers rouge

EmeryCheap and impure form of

natural corundum used for

centuries as a natural abrasive,

largely superceded by synthetic

alumina (corundum) for more

closely controlled grinding.

See also: Carborundum, Corundum, Wet and dry paper

Glossary

Index

11.3

EmissivityThe rate of loss of heat from

unit area in unit time at a

given temperature (usually in

the context of the surface of a

melt). Very dependent on the

principal wavelengths radiated

and the character of the

surface.

See also: Casting temperature, Superheat, White radiation

EthanolAcidified ethanol, silica and

water, hydrolyses to more or

less fluid tetra-ethyl silicate gel

which may be poured into a

mould and set. It may then be

fired to pure silica with

expansion compensating

shrinkage of most cast alloys.

See also: Gypsum-based, Phosphate-based

FeedingThe necessary process of

feeding still molten metal

through gates, sprues and into

the castings, to compensate

for contraction as castings

solidify. Can be gravity or

otherwise pressurised.

See also: Lost-wax casting, Pasty zone (shrinkage), Sprues

Final AssayAnalysis of either individual

components or of an average

sample of a piece of finished

jewellery, perhaps prior to

polishing, that may decide

whether the piece reaches a

(Hall) marking standard.

See also: Fineness, Hallmarking

FinenessPrecious metal content

expressed in parts per

thousand (ppt). In Europe

platinum is usually 950 fine; in

Japan 850, 900, 950 and

999. 14 carat Pt, where

allowed, is 585 fine (but must

also contain 365 ppt of other

PGM).

See also: Carat platinum, Final assay, Hallmarking

FlaskThe outer container of an

investment casting mould,

from the investment process

through to knock-out of the

finished casting. Usually

reusable and in standard sizes.

See also: Invest(ment), Lost-wax casting

FluidityComplex property describing

the ability of molten alloy to

run into a mould and take up

an accurate impression of the

mould. Generally increases

with superheat and freedom

from oxidation. Evaluated by a

variety of empirical testpieces.

See also: Castability, Chilling factor, Superheat

FluxInorganic mixture fusing at a

lower temperature than

melting/soldering/welding an

alloy; cleans exposed surfaces

and protects against reactions

such as oxidation that impair

the melt or joint. Pt alloys

seldom need fluxes.

See also: Induction melting, Soldering, Welding

Fraizer (Fraize orBurr)A range of small tool steel or

tungsten carbide rotors used to

cut a cavity or undercut a

seating to recess a stone.

Fraizes tend to be miniature

circular saws and burrs the

more bulbous or counter-sink

style.

See also: Claw (prong) setting, Bezel setting

Glossary

Index

11.4

Fuel Gas: OxygenRatio (Welding Torch)The volumetric flow ratio

matching the molecular ratio

for complete combustion eg

(2H2+O2=2H2O: ratio 2)

gives a neutral flame with a

sharp inner cone. A lower ratio

gives an oxidising flame;

higher, a reducing flame.

See also: Reducing flame

Grains (or Beads)A decoration medium usually

achieved by fusing scraps of

metal to form tiny spheres by

surface tension onto a surface.

See also: Granulation, Beading Back

GranulationDecoration of a surface by

attaching roundish granules by

fusion (not usually soldered) to

create relief in lines, patterns

or shapes.

See also: Beading back

Gypsum-Based(Investment)A traditional medium refractory

investment based on plaster of

Paris (selected hydrated

calcium sulphate). Not

refractory enough for platinum

alloys but OK for some of the

lower m.pt gold alloys.

See also: Hydrocal, invest(ment), Phosphate-based

HallmarkingStrictly speaking, the term is

only applicable to gold, silver

and platinum goods stamped

as good by UK assay offices

subject to the UK Hallmarking

Act but often applied

unofficially to marking in other

countries too.

See also: Final assay, Fineness

Hot ShortnessBrittleness at high temperature

during working, often

intergranular and caused by

either lower melting point or

other non-ductile grain

boundary constituents.

See also: Ductile, Hot-working, Malleable

Hydrocal A medium refractory form of

gypsum (superior to ordinary

plaster of Paris) based on

carefully controlled calcining to

calcium sulphate hemihydrate

and controlled remixing with

water, retardants or

accelerators.

See also: Gypsum-based, Phosphate - Based

Induction MeltingHeating to above the melting

point by generating eddy

currents within a conducting

material surrounded by a

water-cooled copper coil

carrying an alternating current

at medium (>150Hz) or high

(>1kHz) frequency. Also

creates a stirring effect.

See also: Casting grain, Casting temperature, Superheat, Gypsum-based

Infra-Red RadiationRadiation of longer wavelength

than the visible red (say,

750nm and above) not seen

by the eye but nevertheless felt

by the body as heat. More

easily reflected than ultra-

violet.

See also: Emissivity, Ultraviolet radiation, White radiation

Invest(ment)Pouring a fast-setting slurry of

silica flour and binder (ethyl

silicate or acid phosphate)

around a plastic or wax pattern

with detailed accuracy.

See also: Lost-wax casting, Phosphate-based, Refractory

Glossary

Index

11.5

Jewellers Rouge (andCrocus)Finely ground red to purple

ferric oxide, often bonded with

wax, polishing medium for

jewellery metals which tends to

burnish rather than cut. Often

preceded by decreasing grades

of carborundum and followed

by tripoli or fine alumina

polishes.

See also: Corundum, Tripoli, Wet and dry paper

Jigging Temporary location of adjacent

components prior to welding or

soldering with clear access for

torch and filler but preventing

sagging. Jigs can be used as

heat sinks but must not

contaminate. Most are spring

clips off universal joints.

See also: Soldering, Welding

KerfThe slit, notch or channel

made by a saw in cutting but

also refers to the width of the

cut and the volume of material

made into swarf.

See also: Machinability

LaserLight amplification by

stimulated emission of

radiation results in brilliant

beam of monochromatic light

that is highly directional and

may be focused.

Laser MarkingSome laser machines are

designed for marking. They

have relatively shallow

penetration but very precise

control of movement between

the beam and the target like a

miniature CAD-CAM machine.

Capable of reproducing fine

text, logos and background

textures. Best with flat targets.

Laser PulsingThe operating parameters of a

laser machine are effectively

controlled by the intensity,

length (duration) and frequency

of repetition of pulses.

Intensity is controlled by

energizing voltage and the area

targeted.

Laser WeldingThe light beam emitted by a

laser is focused on a small

area to generate heat at

megawatts/cm2 with rapid

pulsing. The focused energy is

sufficient to cause welding (not

necessarily needing to melt the

Pt) of thin sections.

See also: Spot welding, Stitch welding

LiquidusA line on an equilibrium or

constitutional diagram (which

plots the disposition of phases

in an alloy with temperature

and composition) above which

the only stable phase is liquid

(molten) metal.

See also: Casting temperature, Solidus, Superheat

Lost-Wax(Investment) CastingUsed many centuries ago for

sculpture: now adapted to

investment casting to make

intricate castings to close

tolerances. Wax or plastic

patterns form the cavity in the

investment and these are

melted out in the firing of the

mould.

See also: Invest(ment), Wax models

MachinabilityA qualitative term suggesting

the relative ability of a metal to

be cut in a machining

operation with minimum power,

producing a good surface

finish, clearing swarf efficiently,

all at maximum speed.

See also: Redundant Work

Malleable(Malleability)Capable of being hammered or

rolled extensively without

excessive work-hardening and

cracking. Malleability usually

increases with temperature,

except for hot-shortness.

See also: Cold-worked, Ductile, Hot-shortness

Glossary

Index

11.6

Mandrel Tube-Drawing Uses a hard straight rod or

wire to form the inside cross-

section of a tube during cold-

drawing through a die, so

reducing the wall thickness.

Used for relatively short lengths

instead of plug-drawing more

continuous lengths.

See also: Cold-worked, Section drawing, Work-harden

Millegrain (orMilgrain)A setting tool consisting of a

fine wheel used to roll a

millegrain border around the

edge of a box or bezel setting

around the stone.

See also: Bezel SettingBurnisher

Negative ToleranceUsed in the context of

standards of fineness, and

(Hall) marking, implies a small

compositional allowance below

the specified minimum that is

still acceptable in some

countries.

See also: Fineness, Hallmarking

Nozzle/Tip (WeldingTorch)Describes the type (Nozzle-

mixed or Injection-mixed) and

the size (usually the bore,

often in SWG sizes) of the

gas/oxygen mixture exit

controlling the flame diameter.

Gas velocity controls the flame

length.

See also: Fuel gas: oxygen ratio, Reducing flame

Oil-QuenchingAn alloy steel requiring

quenching to harden at a rate

intermediate between severe

water quenching and mild air-

cooling. Most alloy and tool

steels may be hardened by oil-

quenching, in medium to large

sections, to minimise cracking.

See also: Air-HardeningQuenching

Onglette GraverA short narrow engraving tool

for gouging metal using a

working face rather like a

miniature pointed finger nail;

useful for cutting side seating

in a channel setting.

See also: ScorperBurnisher

PaillonsSmall fragments of solder

clipped from foil, thin strip or

sheet, placed at intervals

across the potential joint zone

and progressively flowed by the

on-coming flame. Often

located by a spot of flux.

See also: Flux, Soldering

Pasty Zone(Shrinkage)From liquidus to solidus,

liquid/solid ratio decreases

from fluid liquid, through pasty,

to fully solid. Feeding shrinkage

with still liquid alloy under

these conditions can be

difficult. Pt alloys do not

usually show pasty zone

problems.

See also: Feeding, Liquidus, Solidus

PatternA master (usually metal) or

consumable (lost wax process)

model of a component to be

reproduced by casting. Pattern

dimensions may need to allow

for net shrinkage or expansion

over the whole casting

process.

See also: Ethanol, Gypsum-based

Glossary

Index

11.7

PavilionThe lower part of a facetted

gemstone below the girdle; the

facets are either angled to

maximise total internal

reflection in highly transparent

stones or deep cut to

maximise colour.

See also: Crown (Facets)

Phosphate-Based(Investment)Investment with acid-

phosphate and magnesia,

which first gels silica flour and

then bonds it by subsequent

dehydration. Working time

rapidly decreased by increasing

temperature.

See also: Ethanol, Gypsum-based

PlanishingSmoothing by overlapping light

blows between a polished anvil

or stake and a polished (1/2lb)

hammer face. The piece is

gradually rotated between tool

blows that cold-work the

surface rather than in depth.

Planish marks may be left in

for decoration.

See also: Cold-worked, Stake, Work-harden

Platinum GroupMetals (PGM'S) Platinum is rarely mined pure.

It usually occurs native as the

metal but often alloyed with

rhodium, osmium, palladium,

iridium, and/or ruthenium:

these collectively forming the

platinum group of metals.

See also: Carat platinum, Fineness

PressingUsing a hand operated (fly-

press) or mechanical press to

produce a batch of similar

components. May involve

stretch-forming, deep-drawing,

coining, blanking, stamping,

simple or complex bending. For

jewellery, a cold-working

operation.

See also: Cold-worked, Malleable, Work-harden

PumiceSpongy, volcanic rock used a

powder mixed with vegetable

oil and applied to a felt bob or

in lump form to remove

scratches and file marks.

Usually coarser than Water of

Ayr Stone.

Q-SwitchDevice in a laser generator

that controls the pulsing of the

laser beam. Usually a quartz

crystal activated by sound

waves through a piezoelectric

transducer attached to the

side of the crystal and fed with

radio frequency power.

QuenchingRapid cooling in a fluid which

can be a cool air blast but is

more likely to be water, for

platinum.

See also: Annealing, Flask

Reducing FlameA melting, annealing, soldering

or welding torch flame with

more gas than can combine

with the injected oxygen or air.

Platinum itself does not oxidise

even with excess oxygen but

some of its alloying

constituents do.

See also: Annealing, Fuel gas: oxygen ratio, Soldering

Redundant WorkWork done in overcoming

external friction and in

unnecessary reversals of metal

movement in the plastic

working and the machining of

metals.

See also: Machinability

Refractory(Materials)High melting point materials

used for furnace linings,

crucibles, moulds. Often need

a suitable binder to hold the

refractory particles together.

Thermal shock resistance,

acidity/basicity, surface finish

(for moulds) also important.

See also: Corundum, Invest(ment), Silica

Glossary

Index

11.8

RepousséTechnique for producing an

ornamental surface by

hammering into relief from the

reverse side while using a firm

but yielding support. Smaller

scale and more detailed than

embossing. Often used with

chasing.

See also: ChasingEmbossing

RetarderMany organics and colloids

retard the start of setting of

gypsum-based investments

because they decrease the

solubility of hemihydrate. This

increases de-airing and

working time.

See also: Accelerator, Invest(ment), De-airing

RollingThe most used cold-working

process for jewellery alloys.

Uses plain faced polished rolls

for sheet and strip: grooved

rolls for bar, rod, and simple

sections; patterned rolls for

continuous embossing. %

reduction in cross-section = %

cold-work.

See also: Cold-worked, Semis, Work-harden, Wrought

Ruby PowderPolishing powder, more likely to

be finely ground haematite

(iron oxide) than corundum

(alumina, ruby)

See also: Jewellers rouge

ScorperA short cutting tool with a

chisel face, used for cutting or

improving narrow channels in

metal: usually broader than a

graver.

See also: Onglette graverBurnisher

Section DrawingStretching out and cold

drawing the cross-section by

pulling through a die after

pointing the lead end.

Reduction in cross-sectional

area is a measure of the

degree of working. Wire and

tube drawing are the most

common examples.

See also: Annealing, Cold-worked, Ductile (ductility)

Semis (Semi-Fabricated Materials)Stock sizes of a wide range of

shapes (plate, sheet, strip, bar,

rod, wire, tube, blanks, circles)

and tempers (hardnesses),

useful for further handworking

at minimum inventory variety.

Major suppliers stock a

standard range and also make

to order.

SilicaSilicon dioxide selectively

processed to form refractory

and abrasive materials. Exists

as quartz, tridymite or

crystobalite crystalline phases

in equilibrium at increasing

temperatures.

See also: Crystobalite, Ethanol, Phosphate-based

SinkingType of tube-drawing where the

wall is allowed to find its own

thickness (as opposed to

mandrel drawing). Usually, the

actual wall thickness increases

as does the wall thickness as a

percentage of the total cross-

section.

See also: Mandrel tube-drawing, Section drawing

SolderingJoining metal or alloy

components by fusing together

with a further lower melting

point alloy known as a solder.

Often uses capillary forces to

draw the solder into the joint.

See also: Flux, Welding, Wettability

SolidusA line on an equilibrium or

constitutional diagram below

which all stable phases are

solid. Above the solidus there

is an increasing proportion of

liquid phase with rising

temperature until at the

liquidus no solid remains in

equilibrium.

See also: Casting temperature, Liquidus, Lost wax casting

Glossary

Index

11.9

SpinningForming sheet metal into cups

by pushing a smooth-ended

tool against the spinning sheet

to force it onto a former, of the

shape required. Can thin

(usually ) or thicken the

resulting wall. Requires

malleability and ductility.

See also: Cold-worked, Doming, Ductile

Spot WeldingJoining process, usually on

overlapping sheet and strip, by

a short pulse of electric current

led in through copper

electrodes with punch pressure

applied to weld a spot at the

interface heated by local

resistance to or near melting

point.

See also: Laser welding, Stitch welding

SpringinessHaving a relatively high elastic

limit and low mechanical

hysterisis, the alloy, usually

cold-worked, may be deformed

elastically (without acquiring a

permanent plastic set) and

springs back to original shape

with little loss of energy.

See also: Cold-worked, Work-harden

SprueWax "wire" feeder system.

Forms the channel for the melt

to be propelled from the gate

to the casting cavity. Should be

kept short and must not freeze

prematurely.

See also: Feeding, Pattern, Wax models

StakeSteel former, usually with

smooth curved surface, used

for raising metal from sheet to

deeper vessel form.

See also: Planishing, Spinning

Stitch (or Seam)WeldingEffectively, a sequential spot

welding operation that

produces a continuous seam

weld by overlapping spot welds

sequenced by an electronic

controller; the electrodes may

be discs, rather than rods as in

single spot welding.

See also: Spot welding

Stress RelieveLow temperature heat

treatment reducing peak

internal stresses (mainly after

cold-work); no recrystallisation

or phase changes, little change

in hardness, slight increase in

ductility; reduces distortion and

cracking in assembly.

See also: Annealing, Cold-worked, Springiness

Stretch- FormingA sheet pressing operation in

which the punch pushes the

sheet through a die but with

the rim of the sheet restrained

so that radial drawing in is

inhibited. Resultant shape is

stretched around the punch.

See also: PressingDeep-drawingDuctile

SuperheatAn extra margin of temperature

above the melting point of a

metal or the liquidus of an

alloy to impart fluidity during

casting and allow the molten

metal to fill the mould without

premature freezing.

See also: Castability, Casting temperature, Chilling factor

Swaging/SwageBlockRectangular blocks of steel

into which D-Section grooves

of varying widths and depths

are cut. Used for hammering

strip into a sharp gutter shape

when beginning to make a

tube section or for truing up

bar or rod sections.

See also: Mandrel tube drawing, Section drawing

Glossary

Index

11.10

Thermal DiffusivityRatio of thermal conductivity:

heat capacity (density specific

heat). A measure of chilling or

insulation power. High density

and specific heat, but lower

conductivity of Pt, gives its

thermal diffusivity at only about

15% that of silver.

See also: Chilling factor

ThixotropicChange in viscosity due to

alteration in shearing stress in

a fluid, slip or paste;

depending on prevailing

conditions the material

appears fluid, jelly-like or stiff

paste without apparent change

in temperature or composition.

See also: Hydrocal, Investment, Phosphate-based

TIG (tungsten inertgas) WeldingElectric arc between tungsten

electrode and weld face,

shrouded by inert gas (eg.

argon) flowing around

electrode; filler wire may be

fed into the arc. Pt itself does

not need inert gas protection

but the electrode and arc are

stabilised.

See also: Ultraviolet radiation, White radiation

TripoliA jewellery polishing compound

consisting of very fine

diatomaceous silica whose

texture is porous and

absorbtive, suspended in a

waxy medium and loaded onto

the face of a polishing wheel

for medium and fine polishing

stages.

See also: Corundum, Jewellers rouge, Wet and dry paper

Ultraviolet Radiation Radiation of shorter

wavelength than the visible

violet (say less than 400nm)

and capable of affecting the

retina of the eye without being

perceived as colour. Less easily

reflected than infra-red.

See also: Emissivity, Infrared radiation,White radiation

UpsettingEndwise compression of a bar

or wire to increase its cross-

section locally, usually at one

end as for a rivet head. The

volume of head formed in one

"stroke" is limited by the ratio

of unsupported stock length to

head diameter required.

See also: Cold-worked,Ductile, Malleable

VallorbeSwiss town noted for

production of watch, clock and

jewellery-making high grade

tools: blades, files, gravers etc.

Wax ModelsWax replicas of a master

pattern (made by injecting into

rubber moulds cured around

the master pattern) assembled

in groups on sprues and then

melted (lost) out of an

investment mould to leave

precise cavities for casting.

See also: Investment, Low-wax casting, Pattern

Water of Ayr StoneA natural soft slate for

removing scratches, file marks

and firestain from small work.

Supplied in small sticks

ranging from 2mm to 25mm

square section. DIpped in

water, used like a handfile,

often preceded by pumice and

before polishing.

See also: PumiceTripoli

WeldingJoining process in which no

solder is used and the

components are joined by

mutual fusion, with or without

a flux, or by hot solid-to-solid

pressure or hammer welding

(which works well with

platinum alloys).

See also: Flux, Hot shortness, Soldering

Glossary

Index

11.11

ComparativeWeights andMeasures

Wet and Dry PaperWaterproof paper coated with

carefully graded and oriented

silicon carbide particles

(carborundum). Used between

filing and polishing stages.

See also: Carborundum, Emery, Tripoli

Wettability Solders/weld fillers more or

less wet the joint according to

the liquid solid contact angle,

(must be less than 90º).

Mutual solubility lowers the

angle as does flux by removing

insoluble oxide, (not normally

required for platinum alloys).

See also: Flux, Soldering, Welding

White RadiationMixed wavelength radiation in

the visible light range of the

spectrum (say 400 to 750nm)

but may include certain

wavelength peaks (colour

bands) and also associated

infrared and ultraviolet

radiations.

See also: Emissivity, Infrared radiation, Ultraviolet radiation

Work-HardenThe increase in hardness which

accompanies plastic

deformation in a metal.

Alloying usually increases the

work-hardening rate of a pure

metal and increasing working

temperature decreases the

rate (to zero when hot-

working).

See also: Annealing, Cold-worked, Hot-worked

Wrought Semi-Finished (Product)Products intermediate between

cast ingot and finished

components stocked in useful

or standard sizes, typically:

plate, sheet, coiled strip,

circles, bar, rod, extruded

section; usually annealed but

may be half-hard.

See also: Annealing, Cold-worked, Hot-worked

WeightTo Convert

Pennyweights to grams Multiply by 1.55518

Grams to pennyweights '' 0.64301

Ounces troy to grams '' 31.1035

Grams to ounces troy '' 0.0321507

Ounces avoirdupois to grams '' 28.3495

Grams to ounces avoirdupois '' 0.0352740

Ounces troy to ounces avoirdupois '' 1.09714

Ounces avoirdupois to ounces troy '' 0.911458

Pounds avoirdupois to kilograms '' 0.4535924

Kilograms to pounds avoirdupois '' 2.20462

Kilograms to ounces avoirdupois '' 35.2740

Kilograms to ounces troy '' 32.1507

Troy WeightUsed in Weighing the Precious Metals

24 grains 1 pennyweight

20 pennyweights (dwt.) 1 ounce troy

12 ounces 1 pound troy

5760 grams 1 pound troy

The troy ounce is about 10% heavier than the

avoirdupois ounce.

31.1035 grams 1 ounce troy

1 gram 15.432 grains troy

1.555 grams 1 pennyweight (dwt).

Glossary

Index

11.12

Avoirdupois WeightUsed in Weighing the Base Metals

16 ounces 1 pound

16 ounces 28.35 grams

The avoirdupois pound is about 21.5% heavier than the

troy pound.

700 grains 1 ounce avoirdupois

Carat WeightUsed in Weighing Precious and Semi-Precious

Stones

1 carat 0.20 grams

1 gram 5 carats

1 carat 3066 grains troy

1 carat 0.007 ounce avoirdupois

The carat is further divided into points for simple

measurement:

1 carat 100 points

1/2 carat 50 points

1/4 carat 25 points

1/8 carat 12.5 points

TemperatureTo Convert

°Fahrenheit to °Centigrade (Celsius) = Subtract 32 from

degrees Fahrenheit, multiply remainder by 5, divide the

product by 9.

°Centigrade to °Fahrenheit = Multiply degrees

Fahrenheit by 9, divide product by 5, and add 32.

°Centigrade to °Kelvin: Zero degrees Kelvin equals -

273°C and thus add 273 to the Centigrade reading to

get Kelvin.

LengthTo Convert

Millimetres to inches Multiply by 0.0393701

Inches to millimetres '' 25.4

Metres to inches '' 39.3701

Inches to metres '' 0.0254

Linear Measurement

1 decimetre = 3.937 inches

1 metre = 39.37 inches

1 metre = 10 decimetres

1 metre = 1,000 millimetres

1 inch = 25.4 millimetres

1 millimetre = 0.0393 inch

1 micron = 0.000039 inch

1 metre = 1,000,000 microns

Area and VolumeTo Convert

Square inches to square millimetres Multiply by 645.16

Square inches to square decimetres '' 0.064516

Square decimetres to square inches '' 15.50

Square millimetres to square inches '' 0.00155

Cubic inches to cubic centimetres '' 16.3871

Cubic centimetres to cubic inches '' 0.061024

Fluid Measurement

1 quart = 32 ounces (fluid) = 2 pints = 1/4 gallon =57 cubic inches

1 gallon = 4 quarts = 128 ounces (fluid) = 3.78 litre and 231 cubic inches = 0.134 cubic feet

1 litre = 1,000 cc (slightly more than 1 quart U.S.) = 0.264 U.S. gallons

1 cubic foot = 7.481 U.S. gallons = 1.728 cubic inches

1 imperial gallon = 1.2 U.S. gallons = 4.59 litre = 277.27 cubic inches

Glossary

Index

11.13