Characterisation of Roman and Byzantine glasses from the surroundings of Thugga (Tunisia): Raw materials and colours

• The paper reports a complete study from the archaeometrical point of view of Roman and Byzantine glass shards coming from the ancient city of Thugga in northern Tunisia, particularly flourishing during the Roman and Byzantine periods.
• The provenance of the raw materials, the flux added and the chromophores responsible for the different colour shades have been investigated.
• The results obtained allow to hypothesize that local production centres were active in Northern Tunisia in these periods.
• The examined shards are quite homogeneous with respects to some glasses reference groups already published in the literature even if some different recipes were employed for the obtainment of the different colours.
• The present study contributes to improve the knowledge concerning the still open question of glass production in the Roman and Byzantine period.

Roman and Byzantine glass shards collected during excavation campaigns around the ancient city of Thugga in northern Tunisia have been characterised by means of various analytical techniques. Portable X-ray Fluorescence (pXRF) was used to determine the glass matrix elemental composition and to identify the elements responsible for the colour. Fibre optic reflectance spectroscopy (FORS) was employed to investigate the chemical nature, the oxidation state and the coordination of the chromophores. X-ray photoelectron spectroscopy (XPS) was here exploited for characterising the outermost layers of the glasses. Elemental analyses by pXRF pointed out that Si, Fe, Al, Ca, K, Rb, Sr, Na and Mg are the main elements present in the glasses. The chromophores responsible for the different shades are Fe for the green shades, Cu and Co for the blue ones, Mn, also used as discolouring agent, for the colourless samples. In relation to the raw materials used for glass production, the comparison with control groups of samples from Northern Tunisia suggests a common provenance of sands.