Ancient glass deterioration in mosaics of Pompeii

The aim of the present project is to evaluate the deterioration degree of ancient glass surface used as mosaic materials (tesserae) in Pompeii's 'ninfei a scala'. Specimens come from the fountain in the 'Domus del Centenario' (Pompeii, IX, 8), built starting from the 1st century AD and have been studied within a broader project on the Domus involving archaeologists, engineers, geologists, chemists and materials scientists. Using data from both non-destructive analyses (OM, XRD, SEW-EDS and UV-VIS) and those requiring few milligrams of specimens (DTA-TGA and ICP-AES), a complete database of the tesserae based on classification by colour, materials characterisation and evaluation of their deterioration have been constructed. After characterisation, specimens were replaced in their original position in the mosaic using suitable mortars. One of the glassy tesserae that was analysed for surface deterioration gave interesting results. The glass, coloured opaque red from Cu2O micrometric crystallisation, turned green on the surface as a result of copper and lead leaching out and depositing as carbonate and sulphate salts. The glass production technology appeared to be very similar to that found in Nimrud (north Iraq) during the 8th century BC, the glass showing a similar chemical composition and deterioration. The identification of colour variations makes it possible to correctly read the decoration system and the archaeometric analysis will help to identify the site and production technique of materials.