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How does cupellation help separate lead from gold and silver?

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A worker in safety gear walks beside a conveyor belt carrying ore at the Tanami gold mine in the arid, expansive landscape of the Tanami Desert. — gold processing The Tanami gold mine, Northern Territory, Australia.

Cupellation is a refining process used to separate precious metals like gold and silver from base metal impurities, such as lead.12

The process involves placing the impure metal alloy into a cupel, which is a flat, porous dish made of a refractory material capable of withstanding high temperatures. The cupel is then heated in a furnace while a blast of air is directed onto the molten metal.12

Under these oxidizing conditions, the lead and other base metal impurities oxidize. The resulting oxides are either partially vaporized or absorbed into the porous structure of the cupel. Because gold and silver do not oxidize under these conditions, they remain behind as a purified metallic bead, often referred to as doré. This technique is a critical step in assaying, allowing for the accurate determination of precious metal content in metallurgical samples.13