Bullion is gold, silver, or other precious metals in the form of bars or ingots. Typically, bullion is used for trade on a market. The word "bullion" comes from the old French word bouillon, which meant "boiling", and was the term for the activity of a melting house.The value of bullion is typically determined by the value of its precious metals content, which is defined by its purity and mass. To assess the purity of gold bullion, the centuries-old technique of fire assay is still employed, together with modern spectroscopic instrumentation, to accurately determine its quality to ensure the owner receives fair market value for it. It is also weighed extremely accurately.
Retailers may sometimes market ingots and bars of base metals, such as copper, nickel, and aluminium as "bullion", but this is not a widely accepted definition.