During cupellation the lead is oxidized to litharge (PbO), most of which is absorbed by the cupel, leaving at the finish a bead of gold, silver, and most of the platinum and associated precious metals that may be present.  The bead is subsequently treated to determine its precious-metal content.

The lead button for cupellation is typically generated in the crucible fusion from the fire assay process, but can also be produced by a scorification assay, or a bullion assay where the precious metal is wrapped in lead foil.