Copper and antimony isotopic analysis via multi-collector ICP-mass spectrometry for provenancing ancient glass

Abstract

Variations in the isotopic composition of Cu and Sb as determined using multi-collector ICP-mass spectrometry (MC-ICPMS) have been investigated as a proxy for provenancing ancient glass. Cu and Sb were added during the manufacturing of ancient (pre-Roman and Roman) glass to obtain colour and opacity. In previous work, the analytical methodology for sample digestion and isolation of Sb preceding isotopic analysis via multi-collector ICP-MS was developed. Although applications of Cu isotopic analysis can be found in the literature, this approach has not been used for provenancing glass raw materials yet. Therefore, the protocols for digestion and Cu isolation were optimized and validated, relying on the use of both an in-house multi-elemental standard and NIST SRM 610 glass reference material. The methods for Sb and Cu isotopic analysis were subsequently applied to a series of late Bronze Age Mesopotamian–Egyptian to Hellenistic–Roman glasses. Results obtained show that the isotopic composition of Cu, expressed as δ⁶⁵Cu, varies from −1.9 to −0.2‰, thus covering a range of approximately 2‰. Unfortunately, the use of Cu isotope ratios to characterize raw materials used in glass manufacturing is complicated by the fact that Cu ores from within a single deposit can exhibit a similar range in δ⁶⁵Cu values, certainly for co-existing Cu sulfides and oxides. Sb in stibnite ore, on the other hand, only shows a variance in isotopic composition of ∼10 ε units (or 0.1‰), but Sb isotopic analysis offers more potential to pinpoint the location of an antimony source used in antiquity.