assayer

An assayer is a professional who determines the composition and quality of metals and ores through chemical or instrumental analysis. Historically, assayers played a crucial role in mining, precious metals refining, and commerce by certifying the fineness of gold, silver, platinum, and other metals and by issuing official assay reports or certificates. The practice of assay encompasses sampling, preparation, and analysis to determine metal content and impurities.

Assayers may work in assay offices, mining companies, reference laboratories, or governmental standards bodies. Common methods include fire assay for precious metals, a fusion-based technique that uses a flux, followed by cupellation to separate base metals; wet chemical analyses such as acid digestion and colorimetric or volumetric methods; and instrumental techniques such as X-ray fluorescence (XRF), atomic absorption spectroscopy (AAS), or inductively coupled plasma optical emission spectroscopy (ICP-OES). Assay results are reported as fineness or karat for precious metals, or as ore grade or weight percentage of target metals. In many jurisdictions, assay data are used to price bullion, settle mine output, or determine tax and royalty obligations.

Etymology-wise, assayer derives from the French essayer, meaning to try or test, with assay referring to the test itself. Related topics include assay, assay offices, hallmarking, and cupellation.