A legacy dataset of 1329 major element analyses of medieval glass (12 th-15 th centuries) has been compiled and analysed for geographical distribution of compositional characteristics. Three regional compositional types may be distinguished using simple elemental plots, associated with glass production in northwestern France, in the region around the Rhine, and in central Europe. Distribution maps are presented to aid interpretation and use of the data. The application of the approach is illustrated through three case studies. Late thirteenth-early fourteenth century medieval stained glass from York Minster (n=91), late fourteenth-century stained glass from New College Oxford (n=79) and a single medieval mirror found in Egypt were analysed using scanning electron microscopy-energy dispersive analysis. The York coloured and white glasses were identical and consistent with an origin in NW France. In the late fourteenth century, the coloured glass samples from Oxford were from the Rhenish region, while the white glass is consistent with an origin in NW France or England. The mirror glass from Egypt is of central European origin, and similar mirror glass is known from Italy. The apparent dominance of German mirror production may reflect an advantage of the glass, which is low in iron. The meta-analysis of the legacy data shows significant potential for developing an understanding of the production and movement of medieval glass.
A large assemblage (n = 307) of architectural glasses (tesserae and windows) from the early 8th-century Umayyad residential site at Khirbat al-Minya was analysed by laser ablation inductively coupled plasma mass spectrometry. Trace element patterns are essential to establish the provenance of the base glass, while the comparative evaluation of the colouring and opacifying additives allow us to advance a production model for the manufacture of glass mosaic tesserae during the early Islamic period. The primary glass types are Levantine I and Egypt 1a, as well as a few older, reused tesserae, and Mesopotamian plant ash glass used for amber-coloured window fragments. Chemical data revealed fundamental differences in the colouring and opacification technologies between the Egyptian and Levantine tesserae. Co-variations of lead and bismuth, and copper, tin and zinc in the Egypt 1a tesserae provide first evidence for the production of different mosaic colours in a single workshop, specialising in the manufacture of tesserae of different colours. No such trend is apparent in the Levantine samples. Red, cobalt blue and gold leaf tesserae were found to be exclusively made from a Levantine base glass, indicating that the generation of some colours may have been a specialised process. The same may apply to the amber-coloured window glass fragments of Mesopotamian origin that exhibit very unusual characteristics, combining elevated copper (2% CuO) with an excess in iron oxide (5% Fe 2 O 3). These findings have significant implications for the production model of strongly coloured glass and the exploitation of resources during the early Islamic period.
The surfaces of 30 pieces of glass from panel 3b of the Great East Window of York Minster (1405-1408 CE) were analyzed by handheld portable X-ray fluorescence (pXRF) and small samples from the same pieces were analyzed by electron microprobe (EPMA).Comparison of the two methods reveals significant divergences which are not systematic, particularly for elements lighter than Ti. Rather than a problem with pXRF calibration or correction software, the non-systematic error is attributable to the presence of a thin surface layer of weathered glass. Analysis of the depths of X-ray generation indicate that virtually all X-rays characteristic of Ca and K are generated within the top 50 μm of the glass. However, for heavier elements such as Rb, Sr and Zr, most emitted X-rays are generated below 100 μm. Using pXRF data for the heavier elements, it is possible to replicate the compositional groupings identified by quantitative EPMA. White glass in the window is likely to have originated in England, while colored glasses were probably obtained from the Continent. The alkali contents of the green and yellow glasses appear to have been manipulated to generate their colors. Glass which is medieval in technology but not original to the panel was identified. In particular, zirconium proved a useful indicator of glassmaking regions, and rubidium and strontium were more sensitive to differences between batches, which has interesting implications for future work.
The Corning Archaeological Reference Glasses are widely used as standards in the chemical analysis of archaeological and historical glasses, as their compositions were designed to approximate those of major glass types in antiquity. Since their development in the 1960s, their compositions have been revisited and updated. This paper provides a brief overview of the Corning glasses, and addresses two of the last three elements to be re-evaluated: the recommended values for the concentrations of SO 3 and Cl were, until now, based on theoretical values. Data for these elements were collected using electron microprobe, and used together with published data to suggest new values. Finally, a complete list with the most up-to-date compositions for the four Corning glasses is compiled for the benefit of other analysts.
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