Cupellation

Cupellation, a process by which gold or silver is extracted from lead containing small quantities of the more precious metal. The process depends on (1) the ready formation of lead (litharge), silver, or gold, being not oxidised when heated, and (2) the power which bone ash has of absorbing molten litharge. In assaying, the argentiferous lead is simply heated strongly on a bone-ash cupel, the oxidised lead being absorbed, and a small bead of silver remains. For manufacturing purposes the process is aided by a strong blast of hot air directed on to the molten metals, which assists in the oxidation of the lead, and also blows the litharge formed from off the surface of the metal, the last portions only being absorbed by the cupel.