Colored gems: a review on non destructive and non invasive approaches in art and gemology

The possibility to incorporate high technology instruments into the world of gemstone testing requires constant researches finalized to inspect several challenges as efficiency and performance of various methods, development of comprehensive appropriate databases and establishment of analytical protocols (Barone et al., 2015a). In these perspectives, recent literature has focused on advanced applications in gems studies. For example, several works show the large amount of informationwhich is possible to obtain with portable Raman analysis on precious and fashionable faceted loose gems, available in the gem market (such as emeralds, sapphires and rubies) (Barone et al., 2016a; Barone et al., 2014; Bersani et al., 2014). They demonstrate that the method could help and speed up the certification procedures, allowing to distinguish natural and synthetic gems, identify fakes and possible treatments used to improve their appearance. Moreover, they recommend standard micro-Raman equipmentas fast and easy instrument to support provenance studies, thanks to the analysis of fluid inclusions or of some peculiar spectroscopic regions (as in the case of the OH region in emeralds for the estimation of alkali ions amount). Additionally, these works discuss the combined use of complementary techniques, such as portable X-ray fluorescence (e.g.for the identification of chromophores in colored inorganic gems) or 13C solid state nuclear magnetic resonance (e.g. for the characterization of fossil resins in terms of chemical fingerprint and maturation degree) (Barone et al., 2016b). Even if the aforementioned researches were made on loose gems, they represent a fundamental reference for the identification of gemstones mounted on precious objects or found in unmovable artworks preserved in Museums. In fact, recent measurement campaigns carried out onjewel collections in Sicilian Regional Museum (e.g. “M. Accascina” and “P. Orsi,” in Messina and Siracusa, respectively) have emphasized thepotential of portable Raman instruments for the identification of gems (Barone et al., 2015b; Barone et al. 2016c). Numerous analyses carried out in a really short time and with different excitation wavelengths on a large number of artifacts (necklaces, earrings, rings, brooches, hair clips, precious belts and loose engraved gems) have permitted the fast classification of precious and semi-precious gemological materials, allowing to identify the composition ofinteresting gems as well as reveal misclassification.Reviewing the aforementioned applications, this paper intends to be a practical resource for researchers, gemologists, collectors and Museum curators who would like to go deeper inside in the potential of complementary non-invasive and non-destructive spectroscopic methods that could practically help studies of inorganic and organic gemological materials. References Barone, G., Bersani, D., Crupi, V., Longo, F., Longobardo, U., Lottici, P.P., Aliatis, I.,Majolino, D., Mazzoleni, P., Raneri, S. & Venuti, V. (2014): A portable versus micro-Raman equipment comparison for gemmological purposes: the case of sapphires and their imitations. J. Raman Spectrosc., 45, 2014, 1309–1317. Barone, G., Bersani, D., Jehlička, J., Mazzoleni, P., Raneri, S. & Vandenabeele, P. (2015a): Fast on-site identification of minerals by using portable Raman equipment in gemological trade contexts and in collectors exhibitions. Periodico di Mineralogia, 208, 27-28. Barone, G., Bersani, D., Jehlička, J., Lottici, P.P., Mazzoleni, P., Raneri, S., Vandenabeele, P., Di Giacomo, C. & Larinà, G. (2015b): Nondestructive investigation on the 17-18th centuries Sicilian jewelry collection at the Messina regional museum using mobile Raman equipment. J. Raman Spectrosc.,46, 989-995. Barone, G., Bersani, D., Lottici, P.P., Mazzoleni, P., Raneri, S. & Longobardo, U. (2016a): Red gemstone characterization by micro-Raman spectroscopy: the case of rubies and their imitations. J. Raman Spectrosc., DOI 10.1002/jrs.4919 Barone, G., Capitani, D., Mazzoleni, P., Proietti, N., Raneri, S., Longobardo, U. & Di Tullio, V. (2016b): 13C solid State NMR and µ-Raman Spectroscopic Characterization of Sicilian Amber. Applied Spectroscopy, accepted. Barone, G., Mazzoleni, P., Raneri, S., Bersani, D., Jehlička, J., Lottici, P.P., Vandenabeele, P., Lamagna, A. &Manenti, A.M. (2016c): Raman investigation on precious jewelry collections preserved in Paolo Orsi Regional Museum (Siracusa, Sicily) by using portable equipment. Applied Spectroscopy, accepted. Bersani, D., Azzi, G., Lambruschi,E., Barone, G., Mazzoleni, P., Raneri, S., Longobardo, U. &Lottici,P.P.(2014): Characterization of emeralds by micro-Raman spectroscopy. J. Raman Spectrosc., 45, 2014, 1293–1300.