An assay is a procedure where a property or concentration of a precious metal is measured.

Methods of assay

Precious metal items of art or jewelry are frequently hallmarked (depending upon the requirements of the laws of either the place of manufacture or theplace of import). Where required to be hallmarked, semi-finished precious metal items of art or jewelry pass through the official testing channels where they are analyzed or assayed for precious metalcontent. While different nations permit a variety of legally acceptable finenesses, the assayer is actually testing to determine that the fineness of theproduct conforms with the statement or claim of fineness that the maker has claimed (usually by stamping a number such as 750 for 18k gold) on the item.In the past the assay was conducted by using the touchstone method but currently (most often) it is done using X-ray Fluorescence (XRF). XRF is usedbecause this method is more exacting than the touchstone test. The most exact method of assay is known as fire assay or cupellation. This method is bettersuited for the assay of bullion and gold stocks rather than works or art or jewelry because it is a completely destructive method.