LEAD STANNATE AS COMPONENT OF ANTIQUE YELLOW GLASSY TESSERAE FROM SICILIAN MOSAICS

New investigations carried out on lead stannate (Pb2SnO4) and lead antimonate (Pb2Sb2O7) in yellow mosaic glassy tesserae from archaeological sites of Sicily (Taormina; Lipari, Tusa and Piazza Armerina), dated early than the 4th century AD, allow to confirm the presence of lead stannate in ancient glass dated before the 4th century. The two compounds have been used either as glass opacifiers and colorants. The different refractive index between fine crystals of these compounds and the amorphous glassy matrix, in which they are immerged, prevent the complete light transmittance, giving the typical opaque appearance to the glass. While lead antimonate was used to produce opaque yellow glass from the beginning of glass production up to the Roman period, it was replaced by lead stannate from about the 4th century AD up to the end of the Roman period. Although until today only Lahil et al. (2011) reported the presence of lead stannate in the glass tesserae dated before the 4th century AD, our new results confirm its presence in the investigated yellow tesserae from several mosaics of Sicily dated early than the 4th century AD.