Making a medieval stained glass window: An archaeometric study of technology and production

Medieval stained glass windows are relatively untapped sources of information about medieval technology and production, because the architectural context prohibits sampling glass for chemical analysis. This research focuses on the comprehensive study of York Minster’s Great East Window (1405-1408) through chemical analysis, investigating glass-making technology and provenance, glass-painting craft organisation, and development of a methodology using the in situ technique, handheld/portable x-ray fluorescence (pXRF). This research also drew on historical documentation, art historical information, and analysis by EPMA-WDS, LA-ICP-MS, and TIMS. Poor surface conditions make characterisation of most elements difficult. Through comparing pXRF with other techniques, five quantifiable elements were identified (Cu, Zn, Rb, Sr and Zr). These were used successfully to distinguish glass recipes and batches/sheets of glass, and potentially they may be used to provenance glass (see below). An attachment was designed to mitigate the interference of lead cames, which hold the glass pieces together, enabling high-precision in situ analysis. Elemental analysis revealed two groups, one consistent with glass produced in Staffordshire and the other with glass produced in the Rhenish region. A longer-term relationship between York Minster and the Staffordshire glass-making industry was discussed. Results suggest medieval glass-makers were capable of greater control over colour generation and glass composition than previously recognised. Synthesis of legacy data proved a useful provenance tool, prompting reinterpretation of previous observations that English windows underwent a compositional change at the end of the fourteenth century. Instead of changes in glass-making technology, it appears glass-making production shifted towards the Rhine. This study is the first to apply the concept of the “batch” to study craft organisation in medieval glass-painting workshops. Batches were identified chemically, and their distribution across the window studied. This yielded insights into the window’s production, including identification of cellular-style production. Glass painted by John Thornton, the master glass-painter, is identified/suggested