What is Fire Assay?

Fire assay is a quantitative chemical analysis technique used to determine the concentration of precious metals (primarily gold and silver) in ores, rocks, and other metallurgical products. The process involves completely melting a sample at high temperatures with a mixture of fluxes and lead oxide (litharge). The precious metals partition into the molten lead, which is then separated from the slag. The lead button containing the precious metals is then oxidized (cupelled) in a porous container, leaving behind a bead of precious metals. The bead is then weighed, and further analysis, such as parting (dissolving silver in nitric acid), may be performed to separate and quantify individual precious metals like gold and silver.