Evidence for glass ‘recycling’ using Pb and Sr isotopic ratios and Sr-mixing lines: the case of early Byzantine Sagalassos

The secondary production (working) of glass from imperial to early Byzantine times has been proven at the ancient city of Sagalassos (SW Turkey) by the existence of glass chunks, fuel ash slag and kiln fragments related to glass processing. It had been previously suggested that local green glass might have been recycled from two other locally found glass types (blue glass vessels and chunks and HIMT glass chunks). This paper provides analytical evidence for the recycling of glass next to the use of imported raw glass. The heterogeneous lead isotopic composition of the green and HIMT vessel glass at Sagalassos, with as end members on the one hand the isotopic composition of local blue glass vessels and chunks and on the other hand that of the HIMT glass chunks, could indicate the production of ‘recycled’ glass, although heterogeneous raw materials could have been used. However, the use of Sr-mixing lines confirms local recycling. It is clear that the Sr in the green and HIMT vessels is a mixture of the Sr in the aforementioned end members. It cannot be proved whether the green ‘recycled’ glass was produced from a mixture of chunks alone, or from a mixture of cullet and chunks. Suggestions are made towards the possible origin of the raw materials for the blue and HIMT glass on the basis of Sr isotopic signatures and absolute Sr contents in the glass.