Cupellation

Cupellation is a refining process in metallurgy in which ores or alloyed metals are heated to very high temperatures and subjected to controlled operations to separate noble metals like gold and silver, from base metals like lead, copper, zinc, arsenic, antimony, or bismuth, in the ore. Cupellation is based on the principle that precious metals typically oxidise or react chemically at much higher temperatures than base metals. At high temperatures the precious metals remain separate but the others react, forming slags or other compounds.

Since the Early Bronze Age, the process was used to obtain silver from smelted lead ores. By the Middle Ages and the Renaissance, cupellation was one of the most common processes for refining precious metals. By then, fire assays were used for assaying minerals: testing fresh metals such as lead and recycled metals to determine their purity for jewellery and coin making. Cupellation remains in use.