The aim of this investigation was to establish a Raman procedure for on-site identification of stained-glass windows and their deterioration level. This study of a representative series of stained-glass pieces dating from the thirteenth to seventeenth, nineteenth and twenty-first centuries made it possible to classify the glasses into four types: Type 1 (rare, Ca-rich Na silicate), Type 2 (rare, Na-rich, Ca silicate), Type 3 (more frequent, K-Ca silicate) and a variant of Type 3, referred to as 3bis. Ion exchange of the alkali cations was made in boiling sulfuric acid and related to structural and compositional changes, which were analyzed with IR and Raman spectroscopy, optical microscopy and EDS. Measurements of the film thickness showed a great discrepancy between the ion-exchange rates of K-Ca (Type 3: 60 µm/h) and Na-Ca (Type 2: 15 µm/h) silicates with that of Type 1 Ca-silicate (0.05 µm/h). IR and Raman spectra provided proof that the nanostructure of the glass was modified, chiefly by the downward (Raman) and upward (IR) shift of the position of the main Si-O stretching peak and a decrease in the intensity of the Boson peak, as well as the Raman 580 cm −1 Si-O bending peak. The decrease in intensity of the narrow ∼950 cm −1 Raman peak, assigned to (earth)alkali nano crystallites in the glassy network, is correlated with the K/Na ion loss and glass weathering. Consequently Type 3bis samples are in fact glasses, in which the surface is depleted of K/Na ions. Optical micrographs support the macroscopic compositional and structural heterogeneity of the ancient glasses. This work demonstrates the potential of Raman scattering for in situ measurements of the degree of weathering of ancient stained glasses.

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Abstract. We present a short review of current theories of glass weathering, including glass dissolution, and hydrolysis of nuclear waste glasses, and leaching of historical glasses from an XAFS perspective. The results of various laboratory leaching experiments at different timescales (30 days to 12 years) are compared with results for historical glasses that were weathered by atmospheric gases and soil waters over 500 to 3000 years. Good agreement is found between laboratory experiments and slowly leached historical glasses, with a strong enrichment of metals at the water/gel interface. Depending on the nature of the transition elements originally dissolved in the melt, increasing elemental distributions are expected to increase with time for a given glass durability context.

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