The Use of UV-Visible Diffuse Reflectance Spectrophotometry for a Fast, Preliminary Authentication of Gemstones

The identification of gemstones is an important topic in the field of cultural heritage, giventheir enormous value. Particularly, the most important precious stones, namely diamond, emerald,ruby and sapphire, are frequently subjected to counterfeit by substitution with objects of lesser valuewith similar appearance, colour or shape. While a gemmologist is able to recognise a counterfeit inmost instances, more generally, it is not easy to do this without resorting to instrumental methods.In this work, the use of UV-visible diffuse reflectance spectrophotometry with optic fibres (FORS) isproposed as a fast and easy method for the preliminary identification of gemstones, alternative to theclassical methods used by gemmologists or to Raman spectroscopy, which is by far the instrumentalmethod with the best diagnostic potential, but it cannot be used in situations of problematic geometrichindrance. The possibilities and the limitations given by the FORS technique are critically discussedtogether with the spectral features of the most important gemstones. Finally, the application ofchemometric pattern recognition methods is described for the treatment of large sets of spectral dataderiving from gemstones identification.