World Of Gems Conference 2017 Proceedings Book

WORLD OF GEMS CONFERENCE V - 27 - SEPTEMBER 2017 I dentification of black gems poses a challenge for the gemologist. Unfortunately, most of them are sold with lit- tle or no disclosure of their identity in the market as they are not considered to be valuable. Black gems are certainly at the bottom of the list when popular gems are encountered. Recently, black diamonds are seen in high end jewelry. This paved the way for other black gems to be used as alterna- tives, i.e., synthetic black moissanite, black spinel. There is no doubt that inexpensively produced black materials such as dyed chalcedony and simulants dominate the mass market. Use of many different black materials in place of black dia- mond has recently created an identification challenge for gemologists and appraisers. Of these, several are almost im- possible to identify with conventional gem testing techniques. Along with black diamonds, modern designers are success- fully integrating a number of unusual natural black materials into their work, many of which have not been used in the trade before. The appeal of an uncommon natural gem in de- signer jewelry never fails. These gems may be less recognized varieties of a better-known gem such as black garnet (melanite) or black tourma- line (schorl). Below are some of the natural black gems commonly seen in the market today. • Diamond • Spinel • Sapphire • Tourmaline • Jadeite • Jasper • Obsidian • Chalcedony (Onyx) • Coral • Pearl • Jet There are also man-made black gem materials that may be encountered. Most are used in low end jewelry and sold without disclosure. These include: • Synthetic Moissanite • Cubic Zirconia • Ceramic • Glass • Plastic Others are unexpected materials such as black rocks rather than gem minerals. For example, jewelry designer and gold- smith Cristina Rosich Peris of London, UK uses black slate in her jewelry. The material is a byproduct of natural tiling man- ufacturing from Germany. The manufacturers reject the slate when it has pyrite veins yet it makes an attractive black tablet for setting (Figure 1). It is always interesting to watch the mar- ket for new and unusual materials. IDENTIFICATION CHALLENGES The common identification methods and tools are typically inadequate for detecting many black gem materials. Since the most important gem in this category is diamond, the con- ventional testing tools such as diamond/moissanite tester or determining the RI, SG or spectrum will be insufficient. In this case, getting back to basics is necessary. Microscopy should PAINT IT BLACK: BLACK GEM CHALLENGES Çi ˘gdem Lüle, PhD., FGA, GIA GG BLACK GEMS ABSTRACT FIGURE 1. Black slate and pyrite earrings in gold plated silver. Courtesy of Cristina Rosich Jewellery of London, uK.

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