Identification of gemstone treatments with Raman Spectroscopy

In gemology, Raman spectroscopy is a very useful means not only for gemstone identification, but also because it can be used for the identification of gemstone treatments, which is subject of the present paper. The treatment of emerald fissures with oil and other natural substances to enhance their clarity has been performed for many centuries. Nowadays, emerald fillers also comprise various artificial resins, mainly epoxy resins. Because of the different behavior of these new substances in the stone, the gemstone trade require an identification. This can be performed successfully with Raman spectroscopy, and examples are given. Waxes and resins are also used to impregnate jadeite and other porous stones. Traditionally, these treatments are detected with infrared spectroscopy, but it is shown that Raman spectroscopy is also able to detect such treatments. The newest gemstone treatment concerns brownish diamonds of type IIa. These can be improved to near colorless by an enhancement process developed by General Electric, USA, using high temperature and pressure. A comparison of Raman spectroscopic features in the visible area (luminescence bands) of both treated and untreated colorless diamonds is given. Finally, examples of artificially colored pearls and corals and their detection with Raman spectroscopy are shown.