Window panes of the Certosa di Pavia: Chemical composition,microstructure and alteration

Abstract

The glass panes of five stained windows of the Certosa di Pavia, (representing S. Caterina, S. Gregorio, S. Girolamo, S. Bernardo and the Presepe) have been analysed by electron microscope and electron microprobe to identify the composition, production techniques and alteration processes. Some blue, green and red glass is multilayered, i.e. is of different glass types that are commonly defined as flashed glass in the literature. The glass panes of the Certosa di Pavia show a great variety of composition. Most samples were made of K–Ca glass, but Na–Ca glass is also present. The composition of the Certosa glass is similar to that of European Medieval glass. In the time between 1000 and 1400 AD, beechwood ash was the raw material for the fluxes used by glass makers. The alteration processes reveal a complex sequence with clear successive steps: at an early stage there is a microbe attack, followed by chemical alteration and crystallisation of gypsum.