Bismuth ore preparation. Workers preparing bismuth ore for assaying. The ore is being lifted out of the mine at (upper left, 4) and then heated on wood fires (2). Bismuth is a heavy brittle crystalline metal that up until 1753 was confused with lead, tin, antimony and zinc. Assaying is the analysis of metal ores to determine the proportion of their contents. Taken from The Laws of Art and Nature, in Knowing, Judging, Assaying, Fining, Refining and Inlarging Bodies of Confin'd Metals (1683), John Pettus, a translation of the work by Lazarus Erckern,