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

Abstract 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 Cu2S band running virtually across the entire width of the ingot suggests that it was formed by the reaction of molten Cu with antimonite (Sb2S3). 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.