THE SHORT ANSWER
Fire assay measures a sample; sampling decides what the result represents
Fire assay by cupellation is a long-established laboratory method for determining gold content. ISO 11426:2021 applies to a material considered homogeneous and states a preferred gold-content range plus method modifications and interferences. The headline result can be precise while the commercial conclusion is wrong if the sample was unrepresentative, mixed lots were combined, chain of custody failed or settlement applied an undisclosed correction.
METHOD BOUNDARY
Separate the observation from the conclusion
CHAIN OF RESULT
Audit the path before accepting the assay certificate
Exact included material, exclusions, gross weight and segregation.
Where, how much, by whom and why the method represents the lot.
Seals, identifiers, transfers, witnesses and retained material.
Homogenisation, splitting and contamination controls before analysis.
Method version, replicates, reference materials, blanks and corrections.
Reported fineness, uncertainty, payable recovery, price basis, fees and dispute process.
LABORATORY EVIDENCE
Precision, proficiency and independence answer different questions
Replicate agreement can show repeatability for prepared test portions; it cannot prove that the source sample represented the lot. Reference materials and controls test method performance; proficiency testing compares a laboratory against an external scheme. Accreditation, where applicable, defines a scope. None of these automatically removes a commercial conflict when the buyer, refiner and assayer are the same party.
Before material is cut or melted, agree who chooses the sample, who may witness, whether an independent umpire sample is retained, which method and rounding rules apply, who pays for a re-assay, and which result controls settlement. This is especially important for mixed jewelry, sweeps and scrap that may not be homogeneous before preparation.
PRIMARY AND STANDARDS SOURCES
Methods are only as strong as their scope and controls
- Hallmarking Convention technical decisions separate homogeneity screening from approved analysis and identify cupellation under ISO 11426 for gold fineness.
- ISO 11426:2021 defines cupellation for gold determination in material considered homogeneous and states its preferred range and interferences.
- LBMA assayer proficiency testing and LBMA sampling and assaying show that laboratory performance and representative sampling are separate parts of a defensible result.
Sources reviewed July 31, 2026. Instrument procedures, safety data, standards and acceptance criteria can change. Use the current method documentation for the exact item, instrument, laboratory and decision.
FREQUENTLY ASKED QUESTIONS
Gold fire-assay questions
What is a fire assay for gold?
It is a laboratory method that separates and measures gold from a prepared sample, commonly using cupellation. ISO 11426 specifies the method for material considered homogeneous.
Is fire assay destructive?
Yes. Representative sampling alters or destroys material, and the laboratory procedure consumes the test portion. Agree on sampling, retained material and settlement consequences first.
Is fire assay 100% accurate?
No analytical result is assumption-free. Sampling, homogeneity, weighing, method performance, interferences, corrections, controls, uncertainty and laboratory competence all matter.
Can a fire assay authenticate a whole gold bar?
It determines gold in the tested sample under the method. Extending that result to a whole bar requires a defensible sampling and homogeneity basis plus separate identity and integrity evidence.