The use of antimony and its implication for the luminescence properties of ancient mosaic tesserae

The potential of using luminescence techniques to characterise and eventually to date ancient glass mosaic tesserae has been investigated. A number of ancient mosaic samples coming from the Mediterranean basin have been studied examining the features of their thermally stimulated luminescence (TSL) emission. We have mainly investigated the role played by antimony oxide (III and V oxidation states) in the optical properties of the vitreous tesserae, both ancient and modern prepared ad hoc. The presence of antimony is always associated with relatively higher TSL sensitivities. In the ancient samples, the presence of antimony led to the formation of calcium antimoniate crystals while the addition of antimony oxide to a modern frit did not determine the formation of such crystals. Analysing the characteristics of the different wavelength-resolved TSL spectra, a tentative interpretation of this phenomenon has been put forth.