Scientific analyses for preservation and restoration of XIII – XV century stained glasses

Our study is devoted to the identification of alteration processes at the stained glasses surface and to support conservation and restoration works that require a deepest information on factors which influence the state of preservation for these vulnerable systems of cultural heritage. Broken fragments of glasses with different provenance, fabrication period, morphologies and state of preservation have been compared, namely samples from the Siena Cathedral, work of Duccio di Buoninsegna, and from the church of St. Giovanni in Monte and the St. Petronio Basilica in Bologna, works of the Cabrini family. By means of optical and electron microscopy analyses, we observed two main phenomena of surface alteration: Neocrystallization and leaching process, known for being the principal cause of alteration for this type of ancient glasses. These alterations reveal both different causes and morphological aspects. Leaching process could depend on the cycle of rain and humid period following very dry ones, which are responsible for a variation of pH and for mechanic tension at stained glasses surface.