Bronze-to-brass transition in the medieval Bukhara oasis

The Bukhara oasis, with its unique geographic location, played an important role during the medieval period when it led the region's political development as part of the Islamic world adjacent to the pastoralists in the northern steppe. Such a distinctive geopolitical environment likely left a visible trace in the shaping of material culture, which we tested by focusing on numerous copper-based metal objects recovered from a medieval site near Bukhara, Uzbekistan. Different types of objects including lighting devices, household objects, small buckles, and rings were metallographically examined for their microstructure and alloy composition. A clear sign of technological transition from bronze to brass was consistently observed in all the object types under consideration where scrap bronze served as one of the key raw materials. Large objects were mostly made of alloys containing a substantial amount of zinc. In contrast, the small buckles and rings were strictly divided between those with and without the addition of zinc, suggesting the simultaneous existence of two different alloy traditions regarding the use of zinc. We discuss these analytical results to relate the emergence of such a unique technological tradition to the region's sociopolitical settings.