Refining gold: furnaces, 2,2, and operator, 9. The man near 4 is gradually heating a crucible surrounded by a ring of burning coals: to increase the heat coals were be raked into a smaller circle. From 1683 English edition of Lazarus Ercker Beschreibung allerfurnemisten mineralischen Ertzt- und Berckwercksarten originally published in Prague in 1574. Copperplate engraving.