A dense, hardened mass of residual metal that solidifies at the very bottom of a smelting furnace hearth. Because it forms in the lowest concavity of the crucible, it takes on a distinct convex shape and often contains the heaviest elements or settled impurities from the heat. It must be physically removed before the furnace can be rebuilt or run again.
Heard on the job
We need to chip out the kingpiece before we can reline the crucible for the next campaign.