Browsing by Author "Gillies, Katherine J. S."

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    Decay of medieval stained glass at York, Canterbury and Carlisle Part 1. Composition of the glass and its weathering products
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1988) Gillies, Katherine J. S.; Cox, Alwyn
    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.
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    Decay of medieval stained glass at York, Canterbury and Carlisle Part 2. Relationship between the composition of the glass, its durability and the weathering products
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1988) Gillies, Katherine J. S.; Cox, Alwyn
    The chemical compositions of specimens of weathered medieval stained glass from York Minster and Canterbury and Carlisle Cathedrals (discussed in part 1 of this paper) have been expressed in terms of three reduced variables, "SiO2", "R2O" and "RO", which represent the glass network formers, and the monovalent and divalent network modifiers, respectively. It is shown that the durability of the glass - assessed on the basis of its physical condition - and the identity of the weathering products present on the outer surface of specimens, may be broadly related to the composition of the glass. The types of weathered surfaces which occur on specimens of decayed stained glass in England, and the compounds present in the weathering crusts, are compared with those previously reported for glass from churches on the Continent of Europe — principally in France and Germany — and are found to be closely related. Hydrated silica, however, has been more frequently recorded as a component of the crusts on ancient glass in England. Any influence of climate on the way in which glass weathers could not be detected, nor could the effect of the orientation of the window.