Bismuth behaviour during ancient processes of silver-lead production

Bismuth is one of the main trace elements found in archaeological lead and silver material in very variable contents. As silver refining by cupellation involves the redistribution of some trace elements contained in the initial lead bullion into the litharge and silver phases, an interdisciplinary approach has been carried out to understand the behaviour of bismuth during this process. Twenty-eight fire-assays were processed with seven different Pb-Bi-Ag alloys of various Bi content. A chemical characterization of all products was carried out. Parallel to the experiments, a thermodynamic approach was undertaken. The combination of experiments and modelling shows that the Bi/Pb ratio can be used as a tracer in silver material throughout the whole cupellation process. Bi and Ag contents in metallic lead might as well highlight the metallurgical process used to obtain lead. High Bi contents in silver-lead bullions are shown to notably reduce the silver extraction yield.