A fast non-invasive method for preliminary authentication of mediaeval glass enamels using UV–visible–NIR diffuse reflectance spectrophotometry

In this work we used UV–visible–NIR diffuse reflectance spectrophotometry with optic fibres (FORS) in order to point out differences between mediaeval and 19th–20th century champlevé enamels previously analysed with X-ray fluorescence spectrometry (XRF). FORS spectra of enamels collected in diffuse reflectance mode made it possible to obtain information useful not only for identifying the colourants of the enamels, but also for evaluating the authenticity of the artworks. By means of pattern recognition techniques, it was possible to highlight relevant spectral features useful for the discrimination of objects, the authentication of which was previously verified by means of elemental analysis (XRF). The role of transition metal ions, mainly iron and manganese, in the reflectance spectrum, has been critically discussed. FORS proved to be a highly reproducible technique, capable of detecting the chromophores in a glass matrix in a non-invasive and rapid manner. A comparison with historically accurate reference glass and enamels, together with data from other analytical techniques, was essential for validating the method. Furthermore, once the FORS methodology was defined, the results obtained showed great accuracy and reliability.