On-site Raman identification and dating of ancient/modern stained glasses at the Sainte-Chapelle, Paris

The experimental procedures and most important conclusions of the first on-site Raman study of the stained glass windows in the upper chapel of the Sainte-Chapelle, Paris are discussed. Some of the windows suffered damage during/after the French Revolution and were partly restored in the 19th century. Measurements were performed with a new portable Raman instrument on colourless, blue and green stained glasses. We illustrate how the Raman signature of the glass makes it possible to distinguish between medieval K/Ca or 19th century restored Na/Ca-based silicates and to determine their weathering degree. This is achieved by means of the extraction of vibrational parameters and then processing them, using chemometric approaches, principal components and cluster variation analyses with varying degrees of complexity. The Raman scattering intensity of weathered glasses is used to determine their relative age. The results differ from those presented in the Corpus Vitrearum Medii Aevi (obtained by visual inspection) and therefore demonstrate the need for updating these reports with modern methods such as in situ Raman spectroscopy.