An assay is the process of testing a precious metal to determine its exact composition and purity. It is the scientific verification that a bar or coin contains what it claims.
Assay Methods
### Fire Assay (Cupellation) The oldest and most reliable method. A sample is melted with lead in a cupel (small cup), and the lead absorbs base metals, leaving pure precious metal. Accurate to 1 part in 10,000. ### X-Ray Fluorescence (XRF) A non-destructive method that bombards the sample with X-rays and measures the fluorescent radiation emitted. Quick and convenient but measures only the surface. ### Specific Gravity Test Measures the density of the item. Gold’s extremely high density (19.3 g/cm³) makes it difficult to counterfeit convincingly.
Assay Certificates
When you purchase a gold or silver bar from a reputable refiner, it typically comes with an assay certificate (or assay card) confirming the bar’s weight, purity, and serial number.