The Raman signature of protonic species as a potential tool for dating or authentication of glazed pottery

Abstract

In this study, the potential of Raman spectroscopy is discussed for the comparative dating or authentication of glazed pottery based on the Raman signature of protonic species incorporated in the glazes due to the corrosion processes as a function of time, chemical composition, and environmental conditions. According to the literature and analyses on a reference set of glass samples that had previously been subjected to heavy corrosion in laboratory conditions and extensively studied by Infrared spectroscopy, the accumulation of protonic species such as water and hydroxyl groups on the surface of glassy silicates gives rise to a specific Raman signature in the 2,000-3,800 cm(-1) range. The relative intensity of this Raman signature is mainly considered to act as a means of discriminating between old and modern artefacts. In order to check this hypothesis, glazed pottery with different origins (Chinese and Vietnamese stoneware or celadons, blue-and-white and painted enamelled porcelains, Islamic terra cottas) and different chemical compositions or processing conditions from a wide time span (similar to 1000 to the present) were analysed by Raman microspectroscopy. Further comparative data was obtained by modifying the experimental parameters such as laser wavelength, objective magnification, and confocal hole. The results showed that Raman intensity of the protonic species shows a correlation with age for lead free glazed pottery in the case of celadons and porcelains. The intensity strongly depends on the chemical composition of the glaze as well as the preservation conditions to a certain degree.