ISO 11426:2021
Jewellery and precious metals — Determination of gold — Cupellation method (fire assay)
This document specifies a cupellation method (fire assay) for the determination of gold on a material considered homogeneous. The gold content of the sample lies preferably between 100 and 999,5 parts per thousand (‰) by weight. Fineness above 999,5 ‰ can be determined using a spectroscopy method by difference (e.g. ISO 15093).
The procedure is applicable to most types of gold samples. Some modifications are indicated for specific cases (presence of large amount of base metals, platinum or palladium, silver). It is not compatible with the presence above trace levels of iridium, rhodium and ruthenium (more than 0,25 ‰ for the sum of all three elements).
This method is also intended to be used as the recommended method for the determination of fineness in jewellery alloys covered by ISO 9202.
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Foreword
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
5 Reagents
6 Apparatus
7 Sampling
8 Procedure
8.1 Method selection
8.2 General method
8.2.1 Assay samples
8.2.2 Proof samples
8.2.3 Cupellation and treatment of precious metal buttons
8.2.4 Parting of the silver/gold samples
8.3 Sample with large amount of base metals
8.4 Sample containing platinum or palladium
8.5 Sample with a silver/gold ratio higher than 3
9 Calculation and expression of results
9.1 Proof sample factor
9.2 Calculation of gold content
9.3 Repeatability
10 Test report
Annex A (informative) Concentration of other base metals, affecting the gold result
Bibliography
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Foreword
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
5 Reagents
6 Apparatus
7 Sampling
8 Procedure
8.1 Method selection
8.2 General method
8.2.1 Assay samples
8.2.2 Proof samples
8.2.3 Cupellation and treatment of precious metal buttons
8.2.4 Parting of the silver/gold samples
8.3 Sample with large amount of base metals
8.4 Sample containing platinum or palladium
8.5 Sample with a silver/gold ratio higher than 3
9 Calculation and expression of results
9.1 Proof sample factor
9.2 Calculation of gold content
9.3 Repeatability
10 Test report
Annex A (informative) Concentration of other base metals, affecting the gold result
Bibliography