Mixed Sources of Pb and Sn in late bronze age European tin ingots provide insights into production processes

Tin ingots have been the focus of multi-method studies involving Sn and Pb isotopes, as well as trace element patterns, in an effort to determine provenance. Although they are non-alloyed artifacts, it has been demonstrated recently that the Pb in most tin ingots was acquired from multiple sources. Herein, we re-examine the corpus of analytical chemical and isotopic studies of European tin ingots from prehistory to investigate the nature and extent of metal mixing in these objects. Multi-variable mixing trends were identified in 20% of Uluburun ingots and 50% of Israeli ingots. A general Pb-associated mixing trend observed throughout the full assemblage of oxhide ingots in the Uluburun cargo suggests that the extent of mixing is considerably higher. The absence of mixing patterns in Sn and Pb isotopes and small size of the ingots from SW England suggests simple one-pour casts of small ingots. In contrast, the extensive mixing in large Mediterranean ingots demonstrates that amalgamation and recasting of tin metal was commonplace within this region of extensive long-distance exchange. Mixing trends were also identified for trace elements including Mn, Co, Ni, Cu, Zn, As, Se, Nb, Cd, In, Sb, Te, Ta, Au, and Bi. The complex mixing patterns associated with Mediterranean tin ingots provide new information regarding the habitus of workers engaged in the chaîne opératoire of tin production, including ore purification, contamination during smelting and/or casting, and the recasting of tin to facilitate transport and exchange in the large-scale, standardized markets of the eastern Mediterranean. Given the apparent extent of mixing evident in tin ingots, mixed metal sources must be considered when interpreting the isotopic and trace element compositions of tin artifacts to infer the metal's provenance.