Fungal biodeterioration of stained-glass windows

Biodeterioration of stained-glass windows by fungi was studied using historically accurate glass production methods. Glass reproductions were made according to the chemical composition determined by micro energy dispersive X-Ray Fluorescence of two historical glass windows belonging to King Ferdinand II's collection dating from the 15th and 17th centuries. Three distinct glasses compositions with different colours were selected and reproduced: i) a mixed-alkali colourless glass: ii) a purple potash-glass with manganese as chromophore, and iii) a brown potash-glass coloured by iron ions. The reproduced glass samples, with two initial surface morphologies (corroded and non-corroded), were inoculated with fungi previously isolated and identified on the original stained-glass windows as species of the genera Penicillium and Cladosporium. Physical and chemical glass surface alterations were analysed by means of optical microscopy, Raman microscopy, micro Infrared spectroscopy, and scanning electron microscopy with energy dispersive spectroscopy analysis. Results showed that fungi produced clear damage on all glass surfaces, present as spots and stains, fingerprints, biopiting, leaching and deposition of elements, and formation of biogenic crystals. Therefore, the inoculated fungi were able to biodeteriorate glasses with distinct compositions. Regarding the biodeterioration degree, there were no differences between the initial non-corroded and corroded glass surfaces.