ISO/CD 25643

Jewellery and precious metals — Determination of silver — Cupellation method (fire assay)

Scope

This document specifies a cupellation method (fire assay) for the determination of silver on a material considered homogeneous. The silver content of the sample lies preferably between 400 parts per thousand (‰) to 999 parts per thousand (‰) by mass.
Fineness above 999 ‰ can be determined using a spectroscopy method by difference (e.g. ISO 15096 or ISO 18214).
The procedure is applicable to most types of silver samples. Some modifications are indicated for specific cases (presence of a large amount of base metals, see Annex A). It is compatible with the presence above trace levels of Platinum Group Metals, see Annex B.
This method is also intended to be used as the recommended method for the determination of fineness in jewellery alloys covered by ISO 9202.