Speciation and weathering of copper in “copper red ruby” medieval flashed glasses from the Tours cathedral (XIII century)

Three “copper ruby red” (or “flashed”) glasses from the St Gatien cathedral in Tours (windows from the XIII century) were investigated at the Cu K-edge by synchrotron X-ray fluorescence microscopy and μ-XANES/EXAFS spectroscopies. The spectra are compared to XANES/EXAFS spectra collected for modern glasses synthesized at various O2 fugacities. Two main types of red glasses are present in Tours, which show a distinct Cu speciation. In the first type (“plaqués”), Cu is present as sub-micron metallic nucleates, which coexist with monovalent Cu linear moieties (30:70 at.%). In contrast, the glasses of the other type (“feuilletés”) show mostly monovalent Cu (together with some evidence for metallic Cu in the edge region of the XANES).