Glass mosaic tesserae from Pompei: an archeometrical investigation

This work reports the results of an archaeometrical investigation performed, through a multitechnique approach, on a series of Roman glass mosaic tesserae found in Pompeii excavations. Chemical and mineralogical analyses of mosaic tesserae of different colours were performed in order to single out the colouring and opacifying agents employed in Roman times. Moreover, due to the paucity of information on the production technology of mosaic tesserae, the chemical data are compared with that of common transparent glass found at the same site, in order to evaluate whether vessels and mosaic tiles could have been prepared with the same recipes and starting from the same glass batch. The chemical analyses were performed by Electron Microprobe, whereas the mineralogical investigation on the opaque samples were carried out by coupling Scanning Electron Microscopy and X-ray Powder Diffraction. The results obtained show that all the analysed samples have the typical composition of natron-based glass. The similarities with the chemical composition - at least in terms of major elements - of common translucent glass could suggest the use of the same raw materials for the preparation of the batch. All opaque blue and green tesserae contain crystalline aggregates respectively of calcium and lead antimonates, except one blue tessera, which contains traces of cuprorivaite and quartz (Egyptian blue pigment). The red sample shows the presence of cuprite aggregates dispersed in a lead-rich matrix. This paper is dedicated to the memory of friend and colleague Filippo Olmi, who prematurely passed away few months ago.