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REFERENCEALL LEVELS | METALS

Hot connections are a valuable set of techniques in the jewelry-makers arsenal. Theres nothing like the look of a smoothly fused join, or the sense of accomplishment that comes from an invisible solder seam. But when do you solder and when do you fuse? And what if you cant do either? Heres a breakdown of the most common joins used on the most common

jewelry metals, along with some tips to keep in mind when planning your projects.

Fuse, Solder, or Weld?

Three methods for hot connections: when to use them, and why?by Reidin Dintzner

A fusing solution can facilitate the fusing process. These typically contain small amounts of copper, and work by lower- ing the surface melting temperature of the metal. This creates a eutectic bond, making the surface of the metal act like its own solder. With this wider window of surface-to-core melting points, the metal will fuse at lower temperatures without as much risk of melting. Though these solutions contain copper, the amount is small enough that it does not create a layer of oxidation.

WeldingWelding is a process that joins metals by using heat or pressure to melt the metal around the seam and sometimes adding a filler material to assist the process. This is in contrast with soldering, which involves melting a lower-melting-point alloy to form a bond without melting the metal to be joined. Some metals, like palladium and aluminum, are extrememly difficult to solder due to their specific properties. In such cases, welding provides stronger, more complete joins.

The energy sources used for welding include gas flame, electric arc, laser, electron beam, friction, and ultrasonic. While often an industrial process, welding may be performed in other environments, but is a potentially hazardous undertaking and precautions are required to avoid burns, electric shock, vision damage, inhalation of toxic gases and fumes, and exposure to intense ultraviolet radiation.

SolderingSoldering is a heat-joining process where a filler metal (solder) is heated slightly above its melting temperature while protected by a non-oxidizing atmosphere (usually a flux) and distributed between two or more pieces of metal by capillary action. Once melted, the solder flows into the seam and diffuses in between the grain structure of the metals being joined. When it resolidifies, it joins the metal pieces together. The solder used in this process is usually an alloy of the metal being joined; this way, it melts at a lower temperature than the parent metals while still maintaining both a strong molecular bond and a close color match.

Fusing Fusing is a method of joining metals without the use of solder. It relies on the small temperature window between the metals surface and core melting points to create a diffusion bond at the surface of the metal. Since fusing relies on specific properties of metals to form a strong bond, the metals that are best for fusing tend to be precious metals like gold, platinum, and silver. Though other metals, like copper and steel, can be used as a base for fusing, they require a greater expertise or additional equipment to fuse correctly. Alloys have a wider range of fusing temperatures than pure metals, making some easier to fuse; however, certain alloys will create too much oxidation and must be soldered to create a join.

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ALLOY MELTING TEMPERATUREATURE SOLDER FUSE WELD

PLATINUM

Platinum up to 95% pure 3217F (1769C)

Palladium 95% pure 2826F (1552C)

The platinum family of metals has a high melting temperature but low conductivity, which makes it harder to solder and fuse. Specialized equipment is needed, including high heat and dark welding glasses. Always maintain an oxidizing atmosphere, and avoid a reducing flame; this can cause platinum to become brittle. So can cadmium, which is an ingredient in several gold solders. Platinum alloys often contain either iridium or cobalt; if you have two different alloys, they will not fuse and must be soldered.

Palladium cannot be soldered with a regular torch, and should instead be welded.

GOLD

24k 99.9% pure 1945F (1063C)

22k 92% gold; silver, copper 11791196F (965980C)

18k 76% gold; silver or palladium, copper, zinc

17001730F (927943C)

14k 58.5% gold; silver or palladium, copper, zinc

16151825F (879996C)

Because gold is highly conductive, it heats evenly and is relatively easy to fuse and solder. The percentage of gold for each karat is standard; the other metals in the alloy determine the color and properties of the metal. For instance, 18k gold always has 76% gold, but the alloy for 18k white gold is different from 18k yellow gold. Specific solders are needed to correctly join and color-match specific gold alloys.

While all gold alloys can be soldered, to fuse gold, it is recommended to use 18k or purer.

SILVER

Fine silver 99.9% pure 1761F (961C)

Argentium sterling silver

93.5% silver; copper & germanium 1610F (877C)

Sterling silver 92.5% silver; 7.5% copper 1640F (893C)

Silver is reasonably conductive, and has melting temperatures similar to gold. Fine silver solders and fuses quickly and easily, though fusing should be reserved for smaller joins as the surface-to-core melting temperature range is small. Although it is easy to solder sterling silver, its high copper content causes it to oxidize quickly, making it difficult to fuse without first depletion gilding. Argentium sterling has a similar composition to traditional sterling, but the inclusion of germanium in the alloy makes it easier to fuse; not only does it have a greater surface-to-core temperature range, but the germanium blocks oxidation from forming.

BASE

METALS

Copper 99.9% pure 1984F (1085C)

Brass Yellow (70% copper 30% zinc) 1706F (931C)

Bronze #521 (92% copper, 8% tin) 1880F (1026C)

Nickel silver #752 (65% copper, 18% nickel, 17% zinc)

2030F (1110C)

Steel Mild steel (0.050.3% carbon) 26002800F (14251540C)

Aluminum 99.9% pure 1220F (660C)

Base metals commonly used for jewelry including copper, brass, bronze, nickel silver, steel, and aluminum are harder and have higher melting temperatures than precious metals. Most base metals can be soldered with high-temperature (hard) silver solder with good results. Some metals, like copper, brass, and bronze, have their own formulations of solder available for a better color-match. Aluminum, however, is difficult to solder, and should instead be welded to form a solid join.

Guide to Soldering/Fusing/Welding

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