The hypothesis of a single origin for Eurasian metallurgy has been challenged by the discovery of copper smelting evidence some 7000 years old at Plochnik, a Vincha culture settlement in eastern Serbia. Here, the tin-bronze foil was excavated from an undisturbed context, on the floor of a dwelling structure next to a copper workshop - a single occupation horizon dated to circa 4650 BCE. The tin-bronze foil from the site of Plochnik is therefore the earliest known tin-bronze artefact anywhere, extending the record of bronze making by about 1500 years.
     Two artefacts were analysed for a new study: the foil from Plochnik and a ring from Gomolava. Their shape implies that they were used for decorative purposes. The foil from Plochnik was left in a soft annealed state so that it could be wrapped around a ceramic vessel, while the ring from Gomolava was left in the work-hardened state. The annealing temperatures used were much higher than those required for annealing the pure copper that was the dominant metal of the time. This demonstrates that the metal smiths understood clearly the specific properties and requirements of tin-bronze.
     The disappearance of the complex tin-bronzes coincides with the collapse of large cultural complexes in north-eastern Bulgaria and Thrace in the late 5th millennium BCE. This suggests that these tin-bronzes were 'cultural alloys', their production dictated by culturally embedded desires and preferences.
     What were the advantages of tin-bronzes? The presence of major impurities such as tin, arsenic and antimony improved their material properties: they melted at lower temperatures than pure copper objects, and were easier to cast. These impurities also gave the artefacts a bright yellow colour. Colour has been recognised as crucial in the use of tin-bronzes as an alternative to gold in central Asia, and for the early appearance of brasses from the early 3rd millennium BCE. Colour is particularly interesting in light of the world's earliest gold objects, dated to the mid 5th millennium BCE and deposited in the cemetery of Varna.
     The colour and social significance of gold can be related to the emergence of the early tin-bronzes, and the opportunities the latter might have offered as an imitation of gold. We may add the relatively limited production of both metals, which stands in stark contrast to the massive production of contemporary copper metal implements. Gold and tin-bronzes may have been the reserve of highly ranked individuals.
     The new study provides archaeological and analytical evidence for the independent emergence of tin-bronze production some 1500 years before the first tin-bronze alloys of south-western Asia, and preceding by almost half a millennium the earliest use of natural alloys of arsenical copper, challenging the established sequence of the evolution of metallurgy in western Eurasia.
     Other metals were used in the Balkans at this period. There is evidence of use of both lead and galena from Vincha culture sites and the use of silver is attested by the hoard from the Alepotrypa Cave in Greece, and dated to the mid 5th-early 4th millennia BCE. The near-contemporary use of all these metals in the Balkans defies the conventional narrative of a slow unilinear evolution of metallurgy.
     Balkan polymetallism may have evolved from the aesthetic preferences of the consumer elite at the time. Exploitation of the material properties indicates that metalworkers were actively pursuing various technological solutions, but these technologies were not utilised for the active alloying of two metal components.
     The absence of alloyed metals in these early stages of Eurasian metallurgy has been traditionally ascribed to a lack of technological skills, but the evidence presented by the new study showcases the significant level of metal craftsmanship in the 5th millennium BCE. The reluctance to produce alloyed metals may well have been rooted in cultural as well as technological choices, for instance in the demand for a specific colour rather than advantageous material properties.
     The production of complex tin-bronzes in the Balkans declined towards the end of the 5th millennium BCE, coinciding with the collapse of the gold-using cultures in Bulgaria. Tin-bronzes only re-appeared some 1500 years later, based on cassiterite tin. This alloy was widely adopted across central and south-western Asia, when its production, consumption and trade acted as one of the driving forces behind the intensification of the economic, social and political lives of Bronze Age communities across Eurasia.

Edited from Antiquity (December 2013)