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Howard has found a crucible. These are made of unglazed, fired fireclay and are used in the assay process. Crucibles can be reused several times. The assayer would grind a certain amount of ore and add it and fluxes to the crucible. The mixture is then heated in a hot assay furnace. The product is poured into a metal mold that's in the shape of an inverted cone. The silver and gold would sink to the bottom tip of the cone and after hardening the slag would be broken off to reveal the button of metal and litharge, or lead oxide, which results from the fluxes.