Biodeterioration of historic stained glasses from the Cartuja de Miraflores (Spain)

Glass samples obtained from five stained glass windows located on the northern side of the Cartuja de Miraflores Monastery (Burgos, Spain) were characterized using UV/Vis spectrophotometry, X-ray fluorescence, optical microscopy, field emission scanning electron microscopy and energy dispersive X-ray microanalysis. Every sample presented evidence of strong superficial deterioration. In general, the external sides of the glass fragments showed a worse state of conservation than did the internal ones. The superficial morphology of the glass exhibited numerous alterations, forming strongly adhered crusts of variable extension and colour, depending on the sample. On the external sides of the glass samples, heterogeneous, dark brown and interconnected crusts, covering most of the glass surfaces, appeared, together with craters and pits filled with whitish deposits. The internal sides showed small craters and pits and a slight accumulation of corrosion deposits. Microbial colonization on this historic glass was observed and both bacteria and fungi were characterized by molecular methods using polymer chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE), complemented with cloning and sequencing of the PCR amplified products. Molecular characterization of the microflora colonizing the glass showed the presence of Eukaryotic genera such as the fungus Aspergillus and the stramenopile Labyrinthula, as well as an associated bacterial community.