Color enhanced woodcut showing workers purifying silver. For coins--the use to which most silver was put--the metal obtained by the cupellation of lead was not the best, because it contained too much undesirable material. It was necessary to purify it still further, by smelting it in a porous mould prepared in a pot full of ashes, which absorbed the undesirable constituents of the alloy. This woodcut from Lazarus Ercker's 16th century book shows the far more efficient method of purification in a muffle furnace. Ercker was an important German writer on metallurgy, as well as an assayer and control tester.