Recycling Cupellation Waste in Glass Production: Evidence from Blihun Hanben and neighbouring sites in Taiwan

This study investigates cross-craft interactions between glass production and cupellation, a process where lead-rich metal is refined into silver using a bone ash cupel. Materials from the Blihun Hanben site in northeastern Taiwan are analysed, with comparisons to other sites along the northern and eastern coasts of Taiwan. The focus is on two types of glass beads: yellow beads containing lead-rich bone ash and cylindrical orange beads with bone ash-containing fritty cores. SEM-EDS analysis reveals that the yellow beads are South Asian m-Na-Al glass, with bone ash high in CaO, P2O5, and PbO, often associated with lead stannate (Pb(Sn,Si)O3) colourant crystals. One yellow bead showed silver-rich areas, suggesting the use of discarded cupels in silver refining. The orange beads' fritty cores contain lead stannate and have a composition similar to West Asian plant ash glass, while the outer glass is South Asian m-Na-Al. A sample containing anglesite (PbSO4) in the inner core further supports the recycling of cupellation waste in glass production. The presence of bone ash suggests that used cupels, soaked with lead oxide, may have been repurposed as raw materials for producing yellow lead stannate for glass colouring. These findings point to a connection between cupellation metallurgy and glass production, with used, discarded cupels likely transported to distant glass workshops. The South Asian m-Na-Al glass recipe in both the yellow and orange glass suggests that these practices may have taken place in India. Literary sources referencing bone or skull powder support the potential link to cupellation practices in India, warranting further investigation. This research raises significant questions for understanding ancient craft interactions and materials circulation.