It is not crystal clear: “nuances” in the selection of raw materials for Iron Age translucent glass revealed by chemical analyses of beads from central Italy

The Iron Age was a period of change, with many innovations in the glass-making technology. The chemical composition of the set of objects considered in the present study demonstrates the diversity of the raw materials used and the depth of knowledge about the manipulation of glass appearance in the eighth-sixth centuries BCE. The study was carried out using fibre optics reflection spectroscopy and portable X-ray fluorescence spectrometry at the museums' premises to examine a large number of glass beads and preliminarily group them on the basis of their composition and spectral characteristics. In addition, a smaller set of selected samples was analysed by laser ablation inductively coupled plasma mass spectrometry to provide a comprehensive chemical characterisation of the material. The compositional data indicated that the samples belonged to the high magnesium and low magnesium glass compositional types. Only one sample was recognised as low magnesium medium potassium glass. Glasses within each group were made from different sands, suggesting different provenances. Some of the samples were suggested to be of local origin, while the others were interpreted as imported glass. Evidence of glass colouring, decolouring and recycling are also discussed.