The Raman signature of protonic species as a potential tool for the dating/authentication of glazzed pottery.
Résumé
Pottery are generally considered as one of the most durable materials. However, all silicates tend to corrode as a function of time, chemical composition and in the presence of acidic water. The potential of Raman spectroscopy is investigated for the comparative dating/authentication of ceramics on the basis of Raman signature of protonic species incorporated in the glaze surface layer. As supported by the literature and analyses on a reference set of glass samples which had previously been subjected to heavy corrosion and extensively studied by Infrared spectroscopy, accumulation of protonic species such as water and hydroxyl groups on the surface of the silicates gives rise to a specific Raman signature in the 2000-3700 cm-1 range. The intensity of the observed bands is mainly considered to act as a tool for discriminating between old and modern artefacts. In order to get quantitative data, glazed pottery with different origins (Chinese and Vietnamese stoneware/celadons, blue-and-white and enamelled porcelains, Islamic glazed terra cottas) and different conservation conditions from a wide time span (~1000 to the present) were analysed. The results showed that the Raman intensity of the protonic species has a correlation with age for lead free glazed pottery in the case of stoneware/celadons and porcelains.[1] As in the case of the absolute Raman intensity of the glass signature collected for very similar artefacts,[2] the relative intensity of the signature of protonic species proved to be useful as a means of comparative dating/authentication especially for stoneware/celadon and porcelain samples which have a lead free chemical composition. The modern fakes can also be identified by no visible signature of protonic species but fluorescence signal. [1] B. Kırmızı, S. Stephen, Ph. Colomban, Journal of Raman Spectroscopy 2019, 50, DOI: 10.1002/jrs.5558.
[2] Ph. Colomban, Journal of Raman Spectroscopy 2018, 49, 921-934.