Decay of medieval stained glass at York, Canterbury and Carlisle Part 1. Composition of the glass and its weathering products

Abstract

Eighty specimens of weathered stained glass, dating from the twelfth to the fourteenth centuries, from York Minster and Canterbury and Carlisle Carthedrals (England) have been subjected to physical analysis with the aim of characterising the natural, atmospheric corrosion of medieval window glass. The composition of the glass was determined by X-ray fluorescence spectrometry. Eight compounds in the weathering crusts were identified by means of powder X-ray diffraction, infrared spectroscopy and atomic absorption analysis; they were found to be inorganic sulphates, carbonates and hydrated silica. A further three crystalline phases were detected in the crusts, but were not identified. Polished sections of several specimens were examined by scanning electron microscopy and electron probe analysis. It is concluded that not all the compounds present in the weathering crusts are necessarily derived from the decay of the glass.