Red gemstone characterization by micro‐Raman spectroscopy: the case of rubies and their imitations

Abstract

In the framework of a wide project aimed to study the potential of Raman spectroscopy in characterizing gems, jewels and jewellers’ collections, in this work the results of a micro-Raman investigation on red gemstones are proposed. In detail, a set of red gems supplied by a jeweller as representative of the current red gems in the trade were analyzed by using micro-Raman instrumentations equipped with different laser excitation sources. The obtained results allow not only discriminating rubies from simulant and fakes but also achieving useful information on inclusions and treatments, obtaining a complete characterization of the studied red gems. Copyright © 2016 John Wiley & Sons, Ltd

Portable XRF: A Tool for the Study of Corundum Gems

“…The second group (R4, R5, R6, R8 and R10) includes samples exhibiting the lower content in Fe (< 150 ppm) and Ti (< 40 ppm), while V is often absent (except in R5). Considering the origin of these rubies, by combining information from previous Raman spectroscopy studies (Barone et al 2016b), microscopic observations and trace-element chemistry, it is possible to classify gems R2, R9, R13, R15 and R16 as natural rubies (being characterized by the highest percentages in Fe, Ti and V and by the presence of Ga). Quite interesting is the case of sample R9, in which Pb and Zr have been also detected.…”

“…Quite interesting is the case of sample R9, in which Pb and Zr have been also detected. Usually, Pb is considered a proof of synthetic origin; however, from previous studies (Barone et al 2016b), we know that this corundum has been certainly subjected to glass filling and invasive heat treatments (gained from the association of zircon and baddeleyte crystals). Therefore, we can conclude that Pb cannot be always used as origin indicator, as it can possibly be related to glass infiltration treatments, detectable only by complementary microscopic observation and micro-Raman analysis.…”

“…Taking advantage from previous studies that allowed to discriminate corundum among numerous and valuable red and blue gems from a private collection by using Raman spectroscopy (Barone et al 2014;Barone et al 2016b), the most interesting ones from the gemological point of view, namely ten red and nine blue loose gems, have been selected to be analyzed by portable XRF (Figure 1 and Table 1). In order to work in conditions similar to real cases, we studied samples without tags on origin and provenance, so that the only clues on these aspects come from features such as inclusion, growth lines, and color spots by microscopy observations.…”

“…For example, portable Raman spectroscopy has been successfully applied for the mineralogical identification of gems set on jewels preserved in museums (Reiche & Lambacher 2004;Osterrothová et al 2014;Barone et al 2015b;Barone et al 2016a), as well as in the study of loose gems (Barone et al 2016b;Bersani et al 2014). However, the value and the importance of a gem goes beyond its mineralogical composition, as origin (natural or synthetic) and geographic or geological source can add extra information in precious artifacts evaluation and characterization (to detect recent substitutions and/or reconstruct specific trading routes).…”

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…Barone and co‐workers studied red gemstone characterized by micro‐Raman spectroscopy in order to shed light on the case of rubies and their imitations. Their results allow not only discriminating rubies from simulants and fakes but also achieving useful information on inclusions and treatments, thereby obtaining a complete characterization of the studied red gems . Coccato et al described the Raman spectroscopy of green minerals and reaction products with an application in cultural heritage research.…”