ISO STANDARDS & TC 174 REVIEW

Chris Walne

Technical Manager

Goldsmiths Company Assay Office

SCOPE OF ISO/TC 174

• Standardisation in the field of Jewellery & precious metals

• Chairman – Dr Jonathan Jodry (Switzerland SNV)

• Secretary – Petra Bischoff (Germany DIN)

• ISO/TC 174 STRUCTURE

• WG1 - Methods for determining fineness

• WG2 - Diamonds, gemstones and related products

• WG3 - Colours of golds ISO 8654

MEMBERSHIP OF TC 174

P-members

Play an active role in committee work as well as vote on ballots and base their opinions on the consensus of national bodies preferably through their individual national committees.

O-members

Follow the development of standards by commenting on them without active participation.

Membership of ISO TC/174P-members O-members

Armenia (SARM) Cameroon (ANOR)

Austria (ASI) Hong Kong (ITCHKSAR)

Belgium (NBN) Hungary (MSZT)

Bulgaria (BDS) Iraq (COSQC)

China (SAC) Kenya (KEBS)

Czech Republic (UNMZ) Republic of Korea (KATS)

France (AFNOR) Lithuania (LST)

Germany (DIN) Mongolia (MASM) MEETINGS HELD

India (BIS) Oman (DGSM) 2 TIMES A YEARIran (ISIRI) Poland (PKN)

Ireland (NSAI) Romania (ASRO)

Israel (SII) Slovakia (SOSMT)

Italy (UNI) South Africa (SABS)

Japan (JISC) Thailand (TISI)

Norway (SN) Tunisia (INNORPI)

Peru (INACAL) Turkey (TSE)

Russian Fed (GOST R) Zambia (ZABS)

Spain (AENOR)

Switzerland (SNV)

United Kingdom (BSI)

Published Standards of ISO TC/174 developed and reviewed by WG1

• ISO 11210:2014 Determination of platinum in platinum jewellery alloys – Gravimetric precipitation of diammonium hexachloroplatinate.

• ISO 11426:2014 Determination of gold in gold jewellery alloys – cupellation method (fire assay).

• ISO 11427:2014 Determination of silver in silver jewellery alloys – volumetric (potentiometric) method using potassium bromide.

• ISO 13756:2015 Determination of silver in silver jewellery alloys – volumetric (potentiometric) method using sodium chloride or potassium chloride.

• ISO 11490:2016 Determination of palladium in palladium jewellery alloys – Gravimetric precipitation with dimethylglyoxime.

• ISO 11494:2014 Determination of platinum in platinum alloys – ICP-OES method using yttrium internal standard.

• ISO 11495:2014 Determination of palladium in palladium alloys – ICP-OES method using yttrium internal standard.

• ISO 15093:2015 Determination of 999 0/00 gold, platinum and palladium – difference method using ICP-OES.

• ISO 15096:2014 Determination of 999 0/00 silver – difference method using ICP-OES.

• ISO 9202:2016 Fineness of precious metal alloys.

Additional ISO Standards under development or review

• ISO 24018 General requirements for gold 1kg bars

• ISO 23345 Non-destructive determination of fineness by EDXRF

• ISO 11596 Sampling of precious metal alloys in jewellery and associated products

• ISO 10713 Jewellery gold alloy coatings

• ISO 22764 The finenesses of solders used with precious metal jewellery alloys

• STAGES OF DEVLEOPMENT

• NWIP – WD – CD – DIS – FDIS - PUBLISHED

TC/174 Round Robin ISO 15093 Pt >999

Using samples provided by Metalor:

The aim of this proficiency testing program is to get information about the practicality of the method as described and compile analytical data to check the impact of any modifications applied to the method.

It is important to note that ISO methods are likely to deviate from those used in the participating laboratories so they were asked to strictly follow the ISO procedure regarding sample and standard preparation and dilutions.

A list of elements and their recommended emission lines were defined but this list was not exhaustive as some lines may not have been available on a particular instrument.

Scope and Methodology ISO 15093

• ISO 15093 specifies an analytical procedure for the determination of gold, platinum and palladium alloys with a nominal content of and above 999 parts per thousand including alloys according to ISO 9202.

• The sample is weighed and dissolved in aqua regia in plastic vessels to prepare a 10g/L solution and the impurities are determined by ICP-OES. The Pt and Pd content is obtained by subtraction of the total content of impurities in the sample from 1000 parts per thousand.

Reference materials & Calibration standards

• 999.9 Pt & Pd minimum purity for the determination of <999.9 fineness and 999.95 minimum purity for finenesses >999.9

• Due to the instability in solution of some of the elements being analysed, it was decided to split them into 4 separate stock solutions which are stable for at least 12 months when kept under proper storage conditions. However, the calibration solutions which are prepared according to the method, should be made up prior to use as they are unstable over longer periods.

Calibration stock solutions 100ppm each

SOLUTION A (3-7% HNO3)

Ag Al Cd Cr Cu Fe Mg Mn Mo P Ge

SOLUTION B (3-7% AQ. REG.)

Bi Co Ga In Se Sn Te Ti Zn

SOLUTION C (3-7% AQ. REG.)

As Ni Pb Sb Si Tl W Zr Ta

SOLUTION D (3-7% AQ. REG.)

Au Ir Pd Pt Rh Ru

5ml A + B in 50ml volumetric flask = 10ppm in solution

5ml C + D in 50ml volumetric flask = 10ppm in solution

( ALL IN 10g/l Pt or Pd MATRIX)

PLATINUM RESULTS

Pt sample POTENTIAL FALSE POSITIVES?

CONCLUSION• These exercises give valuable information about the practicality of the ISO

methods and whether they are, in fact, fit for purpose. They also enable the user to optimise their own instruments for their own particular applications.

New Project: Non- destructive determination of fineness by EDXRF

• Justification and benefits?

Instrument parameters

• General specifications of the instrument with possible minimum requirements:

• X-Ray tube – Tungsten target

• Voltage – 50kv

• Primary filters – Ni or Al

• Variable collimator size

• Detector – Si PIN or SDD

• Spectral resolution <180Kev

• Detectable elements Ti - U

CALIBRATION

The standards have to be made from homogenous material of known composition and require guidelines on the number of standards and the replicas to be performed during the calibration.

UNCERTAINTY: Reference samples of the same composition have to be tested a minimum of 10 times. Then 3 times the STDEV calculated from those replicas is used to determine the uncertainty of the method. There would also be an uncertainty associated with the calibration standards that should be known and taken into account.

CONTROL OF SAMPLES

• Samples to be analysed or final products must be prepared to try to exclude potential systematic errors such as geometry effects or surface treatments and layers.

SCREENING:

Semi-quantitative analysis to be carried out using a standards free method to determine the alloy composition prior to choosing an appropriate calibrated application.

INITIAL ISO TC 174 XRF FINDINGS

• SAMPLES 18 CT GOLD

• Measure at 5 points

• 60 second measurement time

• Al or Ni primary filter

• 1mm diameter collimator

Calibration Standards

(TC STANDARDS)

Progold sample 543: Fire assay = 752.7 RANGE = 748.5-750.8

(OWN STANDARDS)

Progold sample 543: Fire assay = 752.7 RANGE = 747.3-753.0

Further work ?

• Filter selection Al or Ni?

Thank you for your attention.