| Abstract: | The chemical composition of durable blue soda glass dated to the twelfth century from York Minster, both from the windows and excavated within this building, has been determined by X-ray fluorescence spectrometry. The analytical data are compared with results from specimens of similar date, colour and composition from Old Sarum and Winchester in England and Chartres Cathedral in France. Multivariate analysis of the compositional data reveals that this unusual blue glass may be classified into three principal groups the possible origins of which are discussed. The specimens in one of them are of particular technological interest since they may have been produced from Roman, or slightly later, glass in a manner referred to by the twelfth century monk Theophilus. It is shown that medieval stained glass of the soda-lime-silicate type, vis-a-vis that containing potash as the predominant alkali, is not as rare as hitherto believed. |
