SIST EN ISO 11426:2021 PDF

Overview

EN ISO 11426:2021 - Jewellery and precious metals: Determination of gold - Cupellation method (fire assay) - specifies the classical cupellation (fire assay) procedure for accurately determining gold content in homogeneous materials. The method is optimized for samples with gold fineness preferably between 100 and 999,5 parts per thousand (‰). For fineness above 999,5 ‰ the standard recommends spectroscopy by difference (e.g. ISO 15093). The procedure includes guidance for most gold sample types and provides modifications for samples containing large amounts of base metals, platinum or palladium, or high silver content. It is not compatible with iridium, rhodium or ruthenium above 0,25 ‰ (sum).

Key topics and technical requirements

• Principle: Inquartation with silver, addition of lead, cupellation in a high-temperature oxidizing furnace to form a precious-metal button, parting of silver with nitric acid, and weighing of gold. Proof samples are assayed in parallel to correct systematic errors.
• Scope limits: Preferred gold range 100–999,5 ‰; incompatible with significant Ir/Rh/Ru (>0,25 ‰ combined). Fineness >999,5 ‰ requires spectroscopy methods.
• Reagents: Analytical-grade reagents; low-halide nitric acid; assay-grade lead; high-purity silver (min. 999,9 ‰) for inquartation; pure gold (min. 999,90 ‰) for proof samples.
• Apparatus: Cupellation furnace (1 050–1 150 °C, oxidizing atmosphere - muffle furnaces insufficient), magnesia cupels, annealing crucibles, jewellers' rolls, polished anvil/hammer or press, and an analytical balance (≥0,01 mg; 0,001 mg preferred for fineness >995 ‰).
• Special procedures: Clause 8 addresses samples with large base-metal content, those containing platinum/palladium, and high silver/gold ratios (>3), plus calculation adjustments for added gold and proof-sample fineness.
• Quality and reporting: Use of proof samples, repeatability criteria (updated in this edition), and prescribed test-report elements.

Applications and users

• Laboratories performing gold determination for jewellery, bullion and related precious-metal products.
• Assayers and quality-control teams in jewellery manufacturing and precious-metal refining.
• Regulatory bodies and conformity assessment organizations verifying alloy fineness and hallmarking.
• Useful for forensic and trade laboratories where accurate fire assay results are required and where elemental interferences (Pt, Pd, base metals) must be managed.

Related standards

• ISO 15093 - spectroscopy methods for high-purity gold (reference for fineness >999,5 ‰)
• ISO 9202 - jewellery alloys fineness determination (EN ISO 11426:2021 is the recommended cupellation method for alloys covered by ISO 9202)
• ISO 11596 - sampling procedures for jewellery gold alloys

EN ISO 11426:2021 modernizes cupellation practice by extending scope, clarifying proof-sample purity, adding procedures for difficult matrices, and updating calculation and repeatability requirements - making it a current, practical reference for accurate fire-assay gold analysis.