Are tin oxides inclusions in early archaeological bronzes a marker of metal recycling?

Bronze artifacts from Early Bronze Age in Europe often contain white inclusions in the metallic matrix, that are identified as tin oxides (SnO2 or Cassiterite). These inclusions are interpreted as un-smelted residues coming from the copper ore and are generally mixed with more complex oxidized inclusions, which contain sulfur, antimony, arsenic, silver, nickel and cobalt. The nature, shape and distribution of these partially smelted tin inclusions give information on the alloying process. Depending on the technological context and the geographical areas, the presence of such inclusions might indicate that the material has been produced by selecting and supplementing of raw materials containing SnO2 (e.g. co-smelting). In order to understand the role of tin oxide inclusions in the production of bronzes and possible recycling procedures, a crosscutting investigation has been carried out, based on experimental researches. The results show that tin oxides do not completely reduce after four re-melting cycles (recycling) and such a fact is deeply related to the oxygen availability and the dwell time that influences the kinetics of the reaction.