Archaeometrical analyses of glass cakes and vitreous mosaic tesserae from Messina (Sicily, Italy)

We report the results of a study performed on several glass samples recovered after the destruction caused in Messina by the earthquake of 1908, and stored in the ‘Fiore’ deposit of the Regional Museum of Messina (Italy). The samples, still lacking a reliable classification, are glass cakes, some spare mosaic tesserae, and fragments of a well-dated mosaic (Mosaico dell’Angelo, XIII–XIV century A.D.). EPMA, SEM-EDS, XRPD and XAS were employed to provide a detailed chemical, mineralogical and spectroscopic characterization of the samples. The chemical analyses of major elements show high levels of K2O and MgO, as a result of the prevalent use of plant ashes as flux. The cakes are characterized by a large dispersion of Si, Al and Ca contents, suggesting the use of different starting raw materials. The most common crystalline phases used as opacifiers and colorants are quartz and wollastonite. Crystalline aggregates of SnO2 are present in the gray cakes, whereas PbSnO3 crystals are found in two green mosaic tesserae. All the red samples contain small clusters of metallic copper. On the basis of the chemical composition, it is possible to confirm that most of the samples were produced in the XIII–XIV century, while no specific conclusions were reached on the possible use of the glass cakes as raw glass materials for the production of the investigated mosaic tesserae.