What Is a Gold Assay?

An assay describes the sample tested, so the sample must represent the lot. For homogeneous refined bars this is straightforward; for doré and other variable material, sampling procedure is carefully specified.

Drilling at defined points, taking cuttings during pouring, or melting and sampling a homogenised lot are common approaches depending on the material.

Fire assay separates precious metal from other elements by fusion and cupellation, leaving a bead that is weighed to establish content. It is the long-standing reference method for gold.

It requires a laboratory, trained analysts and controlled conditions, which is why it takes longer than instrumental screening.

X-ray fluorescence and, for high-precision work, inductively coupled plasma techniques are used alongside or instead of fire assay depending on requirements.

Each has a different accuracy profile and a different exposure to surface effects or matrix interference.

A report generally identifies the laboratory, the sample, the date, the method used and the measured content, expressed as fineness or as a percentage.

Which assay information applies to a given transaction is established during the enquiry and due-diligence process.