Structural and vibrational characterization of medieval like glass samples

Within the framework of a project aimed to develop protective coatings for antique glass windows, three glass varieties of medieval-like composition were prepared using recipes deduced from archaeometric studies and different amounts of potassium for fluxing (15-20-25 K2O wt.%). Batches were melted in mullite crucibles using an electric furnace at 1350 degrees C, the glass was fast cooled in air and annealed at temperatures 20 degrees C higher than the sample glass transition temperatures (726, 702 and 683 degrees C for V1, V2 and V3, respectively). The chemical composition of the glass was determined by X-Ray Fluorescence Spectroscopy (XRF) and the glass transition temperature was checked by differential thermal analysis (DTA). X-Ray Powder Diffraction (XRPD) data and vibrational spectroscopic experiments (FT-IR and Raman) revealed a direct dependence of glass de-polymerization on potassium content. In particular, the Raman data were interpreted on the basis of SiO4 structural units Q(n) and the polymerization index I-p