Characterization and ageing of medieval-like glasses for the Design of protective coatings

Glass, compositionally similar to that of the medieval stained glass windows, was produced and characterized through a multi-technique approach to investigate the structural modifications induced by different amounts of potassium as flux, and their influence on the glass alteration processes. Ageing experiments were performed simulating separately the two mechanisms responsible for the glass alteration: leaching and dissolution. A clear relationship between the glass K-content and the degree of depolymerization of the silicate network was found through XRPD, FT-IR, and Raman spectroscopy analyses. Moreover the ageing experiments showed a correlation between the glass K-content and the alteration degree; in particular, it was observed that the most K-rich and depolymerized samples were also the most alterable. These structural studies were aimed to the design of water repellent protective coatings, matching the requirements of the Conservation of Cultural Heritage. Some hybrid sol-gel coatings, based on TEOS (Tetraethyl- orto-silicate), that guaranties the chemical and physical compatibility with the glass, and the organically functionalized Si-alkoxides, were prepared and characterized to obtain a good water repellency. Their performance was tested through accelerated ageing under UV-light and exposure to SO2-saturated atmosphere.