A geochemical study of Roman to early Byzantine Glass from Sagalassos, South-west Turkey

Abstract

The finding of glass chunks together with fuel ash slag and kiln fragments related to glass processing strongly suggests local secondary production (working) of glass at Sagalassos (SW Turkey) from imperial to early Byzantine times. Chemical evidence shows that different silica raw materials were used in imperial and early Byzantine times for blue and green glass found locally. Colourless glass shows no clear difference in chemical composition and hence in silica raw materials between late Roman and early Byzantine times. Locally found early Byzantine yellow-green glass and chunks correspond to the previously defined Byzantine HIMT glass type. The chemical composition of the glass chunks found, identical to that of the contemporary glass of the same colour, strongly indicates that these chunks were used for the manufacture of early Byzantine green, colourless and yellow-green glass at Sagalassos. The homogenous lead isotopic composition of the chronological groups of blue glass, suggests the use of two distinct but homogenous silica raw materials for the manufacture of this glass. In view of this homogeneity, it is likely that contemporary blue glass was produced at a single location. The linear trend of the heterogeneous lead isotopic composition of the green and colourless glass is a strong indication of recycling effects in the glass composition. The end members of this trend are formed by the isotopic composition of the blue glass on the one hand, and of the yellow-green (HIMT) glass on the other hand. The heterogeneous lead isotopic composition of the yellow-green glass at Sagalassos is probably the result of recycling of this glass, reflecting mixtures of the original lead isotopic signatures of the broken glass and the original HIMT glass chunks. It should be noted that the two main raw materials for primary glass production (silica and soda) were available on the territory of Sagalassos. Moreover, the lead isotopic composition of quartz pebbles sampled from the artisanal quarter of Sagalassos, is similar to that of the local blue glass.