Study of mosaic glass tesserae from Delos, Greece using a combination of portable μ-Raman and X-ray fluorescence spectrometry

During three in situ analytical campaigns, around 270 glass tesserae were analysed by pXRF and nearly 40 tesserae using portable μ-Raman spectroscopy. This integrated approach allowed to gain an overview of the raw materials and the techniques employed in the production of these glasses. In particular, for all the tesserae the use of natron as a flux could be hypothesised. The majority of red glass tesserae were identified as a high-copper high-lead glass generally referred to as sealing-wax. The colourings agents used in the other tesserae (Fe, Co and Cu ions, Pb2Sb2O7) are the common ones used in Antiquity and the antimony-based opacifiers are typical for the considered period and geographic area. Blue and turquoise tesserae remarkably show a highly variable lead concentration which appears correlated with antimony. This correlation raised the hypothesis that an antimony ore rich in lead was used for the opacification of these glasses.