Roman coloured and opaque glass: a chemical and spectroscopic study

This work reports the results of an archaeometrical investigation of opaque Roman glass and is mainly focussed on the role of configuration and oxidation state of copper on the colour and opacity of red and green opaque finds (mosaic tesserae, game counters, and glass artefacts) from Sicily and Pompeii excavations. The glass fragments were characterised by EMPA, SEM-EDS, TEM, and XRPD analyses and the copper local environment was investigated using X-ray absorption spectroscopy. The analyses of high-resolution Cu-K edge XANES and EXAFS spectra suggest that, in red samples, copper is present as monovalent cations coordinated to the oxygen atoms of the glass framework, accompanied by metallic clusters. In green samples all the copper cations are incorporated in the glass matrix.