Microstructure of an extraordinary Bronze Age copper ingot with a high antimony content

The Cu ingot from Velem contains approximately 10 wt.% Sb, 4.5 wt.% As, 1.2 wt.% S and Ag, as well as other trace elements in an amount below 0.2 percent by weight. A Cu 2 S band running virtually across the entire width of the ingot suggests that it was formed by the reaction of molten Cu with antimonite (Sb 2 S 3 ). Remarkably, the generated cutting surface was not copper-colored but had a silvery appearance which, however, can be attributed to the high Sb content. The metallographic examinations revealed a very inhomogeneous structural composition of the ingot. Large areas consist of dendritically solidified Cu, while the interdendritic areas are characterized by mixtures of different phases of the elements Cu-Sb-As-S.