Colourants and opacifiers of mosaic glass tesserae from Khirbet al-Mafjar (Jericho, Palestine): addressing technological issues by a multi-analytical approach and evaluating the potentialities of thermoluminescence and optically stimulated luminescence dating

Abstract

The paper discusses data concerning the secondary manufacture technology of a set of opaque coloured early Islamic mosaic glass tesserae from the qasr of Khirbet al-Mafjar (Jericho, Palestine). Archaeological contextualisation of the site had allowed attributing these finds to the Umayyad occupational phase of the building, and an in-depth study of the composition of the glassy matrix had provided evidence of a double supply of glass from Egypt and the Syro-Palestinian coast occurring in the production of the base glass intended to be used for the manufacture of mosaic tesserae. Here, a multi-methodological approach has been carried out to characterise colourants and opacifiers: visible reflectance spectroscopy (VIS-RS), optical microscopy (OM), scanning electron microscopy coupled with energy dispersion analysis (SEM-EDS), micro-Raman spectroscopy (micro-Raman) and X-ray diffraction (XRD) were performed on the opaque tesserae. Moreover, either optically stimulated luminescence (OSL) or thermoluminescence (TL) protocols for luminescence dating were applied on selected samples, with the aim of relating luminescence properties with the geochemical features of the glass tesserae, in the perspective of deepening the studies towards the absolute dating, an unquestionable help to the stimulating challenge of investigating ancient glass manufacture. Tin-based, phosphorus-based and copper-based opacifiers were identified, and the achieved results suggest the use of the same opacifiers and colouring agents regardless of the different base glass. Furthermore, data obtained by TL and OSL protocols revealed useful and stimulating potentialities these techniques could have in dating opaque glasses.