Small, cup-shaped vessels made of bone ash or porous ceramic material, used in metallurgical refining to separate precious metals from impurities.
From Latin 'cupella' (small cup), which came from 'cupa' (barrel or tub). The word evolved in metallurgical vocabulary to refer specifically to these specialized refining tools used in precious metal processing.
Cupels are made from bone ash because it has to be incredibly porous and heat-resistant—the bone ash can withstand temperatures over 1000°C while absorbing molten base metals without contaminating the pure gold or silver remaining in the cupel.
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