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Article Index- Gemstone Enhancement and its Detection in the 2000s: Clarity Enhancement, Irradiation and Combined Treatments, and Surface Coating
Gemstone Enhancement and its Detection in the 2000s:
Clarity Enhancement, Irradiation and Combined Treatments, and Surface Coating
by Shane F. McClure, Robert E. Kane, and Nicholas Sturman
from GEMS & GEMOLOGY, Vol. 46, No. 3, pp. 218–240.
© 2010 Gemological Institute of America, Fall 2010
Published on JTV.com: January 2012
This is Part II of a four part series on gemstone enhancement. See Part I and Part III.
See the end of this downloadable PDF for About the Authors, Acknowledgments, and a complete list of References.
Advances in technology and increased demand for lower-priced gemstone materials contributed to the proliferation of new treatments throughout the first decade of the 2000s. The developments that made the most difference were the diffusion treatment of corundum with beryllium, diffusion of copper into feldspar, clarity enhancement of ruby and diamond, and heat treatment of diamond, ruby, and sapphire. Gemological laboratories and researchers have done their best to keep up with these treatments, and the jewelry trade has struggled with how to disclose them. This article summarizes these developments and the methods used to identify the various enhancements.
Clarity Enhancement
During the 1990s, clarity enhancement was one of the jewelry trade’s most formidable challenges. Its use with emeralds—in what had basically amounted to a trade secret—was touted publicly and almost caused the crash of the emerald market. In addition, the clarity enhancement of diamonds spread rapidly, with improper disclosure causing the ruin of some businesses. Clarity enhancement has remained a serious issue in the 2000s. However, the methods changed and the focus has been on different gem materials.
Diamonds.
The biggest concern about the clarity enhancement of diamonds via fracture filling revolved around the durability of the glass filler. Damage due to heat (figure 14) from standard jewelry repair procedures, such as retipping, inevitably caused problems at the retail level. One of the major treaters (Oved) announced in 2000 that they had developed a filler that could withstand such heat (Bates, 2000;”Oved announces. . . ,” 2000). However, testing showed that although the new Oved filler material seemed to withstand higher temperatures, it still could be damaged by some jewelry repair procedures, even when performed by a master jeweler (Shigley et al., 2000). Oved instituted a policy of laser inscribing their company name on a bezel facet of all the diamonds they treated so the filled stones could not be misrepresented (Gallagher, 2000).
The practice of laser drilling diamonds to create an opening through which acid could be introduced to remove a dark inclusion had remained unchanged for many years, until a new version was introduced that took advantage of advances in laser technology. Developed in Israel and referred to as the “KM treatment” (short for kiduah meyuhad, or “special drill” in Hebrew; Horikawa, 2001), this method did not actually drill a hole into the stones. Instead, it used lasers to create a small fracture from the inclusion to the surface so that the inclusion could be bleached without leaving a tell-tale hole at the surface (figure 15; McClure et al., 2000a). Unfortunately, this treatment entered the market undisclosed, and its fraudulent nature caused the Israel Diamond Bourse to outlaw its use. It continues to be encountered, and is often referred to as “internal laser drilling.”
Identification is done with magnification. The laser leaves behind lines or dots of irregular squiggles, with feathers leading from an inclusion to the surface (figure 16). These marks tend to look black in transmitted light, and are usually confined to a feather (McClure et al., 2000a; Cracco and Kaban, 2002; McClure, 2003a). They may be tiny and difficult to find even with a microscope—or large and numerous, easily seen with a loupe.
Other observations were posted in the literature periodically. Among them were changes in flasheffect colors (Cracco and Johnson, 2008), filled fractures in treated-color diamonds (Song et al., 2009; Gelb, 2005), difficult-to-identify damaged fillers (Gelb and Hall, 2005), and fracture filling associated with a pink dye (Yeung and Gelb, 2004).
Ruby.
The first report of faceted rubies showing a flash effect similar to that seen in clarity-enhanced diamonds was in 2004 (“Lead-glass impregnated ruby. . . ,” 2004). Chemical analysis revealed that these rubies were filled with a high-lead-content glass. Soon other labs reported this treatment (“New treatment on unheated rubies. . . ,” 2004; Rockwell and Breeding, 2004; Milisenda et al., 2005).
It became apparent that this treatment was going to be very significant to the industry (Roskin, 2004). The starting material was very low quality, translucent- to-opaque, non-gem rough from Madagascar (Pardieu, 2005). By a process that involved low-temperature heating, cleaning in an acid bath, and then filling with a high-lead-content glass, this non-gem corundum was transformed into transparent, facetable material (figure 17). This made available huge amounts of treated rubies that were usually sold at very low prices.
Identification of these filled rubies was not difficult. Most had so many filled fractures that the flash effect was easy to see with magnification, although the red color of the ruby sometimes partially masked the orange flash (McClure et al., 2006; figure 18). Flattened gas bubbles and high-relief unfilled areas within the fractures were also readily visible with magnification. However, the use of reflected light to look for differences in surface luster was not very helpful in this case. The luster of this glass was very similar to that of ruby, sometimes even higher (Smith et al., 2005), so it was much more difficult to see than the more typical silica glass fillers.
The filler proved relatively durable to heat (up to ~600ºC), but it was easily etched by even mild acids such as pickling solution (McClure et al, 2006). This etching turned the filler white near the surface, rendering it quite visible.
Also of concern was the decreasing quality of the starting material. We began to see stones where the flash was everywhere, and internal filled cavities containing large spherical gas bubbles were common (Scarratt, 2009).
The nomenclature for this treatment soon became an issue. The early material was referred to as clarity enhanced because even though the treatment was fairly extensive, the rubies were mostly solid material that would be expected to stay together even without the treatment. However, some of the later material contained so much glass that it appeared the glass was actually holding the pieces of ruby together. Soaking such stones in hydrofluoric acid to remove the glass resulted in their falling apart along fractures or being reduced to tiny pieces (Scarratt, 2009). Accordingly, GIA developed a threetiered system, keeping clarity enhanced for more solid material, specifying ruby with glass for stones that needed the glass to stay together, and using ruby/glass composite for those composed of unrelated pieces of ruby floating in glass (Scarratt, 2009; figure 19). The other labs of the LMHC adopted these criteria. American Gemological Laboratories (AGL) and the International Colored Gemstone Associ - ation (ICA) have chosen to call all these stones composite ruby.
The real problem, however, is the large amount of this material that is being sold without any disclosure. So far, this treatment has even appeared in ruby beads (Hänni, 2006a), color-change sapphires (Choudhary, 2008), hollowed-out rubies set in closed-back mountings (Krzemnicki, 2007), and estate jewelry (Quinn Darenius, 2010).
Emerald.
The damage caused to the emerald market in the 1990s from lack of disclosure of clarity enhancement slowly began to fade in the 2000s (Gomelsky, 2003). However, the debate over the use of oil versus polymers as filler material continues, and a significant study was done on the durability of fillers (Johnson, 2007).
To address the possibility that a highly fractured stone was masquerading as a much finer one simply because of the treatment, labs started to state the degree of enhancement on their reports (e.g., McClure et al., 2000b). Different systems were developed with anywhere from three to nine categories (Gomelsky, 2001a,b); the most common were threeor four-tiered. Today, degree-of-enhancement calls have become standard procedure for emerald reports from all the major laboratories.
Near the end of the decade, it was reported that some emerald rough was being “stabilized” with hardened polymers, so larger stones could be cut (Roskin, 2007; Federman, 2008). In effect, though, the polymer glues the pieces of emerald together at the fractures (e.g., figure 20), so its removal would result in the stone falling apart (Federman, 2007b). This situation is very similar to that of the lead glass–filled rubies, making disclosure even more important.
Other Materials.
Laboratories have reported on many other filled gems. Some of those mentioned in the 2000s include: aquamarine and tourmaline (Wang and Yang, 2008; Deng et al., 2009), andalusite (Fernandes and Choudhary, 2009), fuchsite quartzite (Juchem et al., 2006), hackmanite (Wehr et al., 2009), and iolite (McClure, 2001).
IRRADIATION AND COMBINED TREATMENTS
Intense colors can be induced in many gems by exposing them to various forms of radiation, such as electrons, gamma rays, or neutrons. To remove unwanted color overtones, some irradiated stones are subsequently heated. While the 1980s saw significant experimentation and development in the area of gemstone irradiation, very few new types of irradiated gems appeared on the market during the 1990s and 2000s. Likewise, little progress was made in detection methods.
For many gems, there is no definitive test or series of tests to establish whether they have been irradiated. Even though irradiation has been used for many years to produce intense colors in yellow beryl, pink-to-red tourmaline, and kunzite, these enhancements remain undetectable. The same is true for blue topaz and many other routinely irradiated gem materials.
Blue irradiated (and annealed) topaz generates more than $1 billion annually in retail sales (Robertson, 2007). The low cost of irradiated blue topaz (typically a few dollars per carat at wholesale) leaves the trade little economic incentive to determine whether or not the gem has been treated. As a result, all blue topaz is assumed to have been irradiated. The same is true for smoky quartz and dark yellow beryl.
Diamond.
With the staggering prices realized at auction for some fancy-color diamonds during the last decade (e.g., more than $1 million per carat for some natural-color blue and green diamonds), there is huge incentive to determine whether a diamond’s color is natural or irradiated. Large quantities of diamonds continued to be irradiated (often followed by low-temperature annealing at atmospheric pressures) to produce a wide variety of colors—red, orange, yellow, green, blue, violet, and purple—in saturations from light to very dark (see Overton and Shigley, 2008; Shigley, 2008). Many treaters produced small faceted irradiated (and annealed) colored diamonds for use in jewelry.
The most significant developments in diamond irradiation since 2000 were in combination treatments. Both natural and synthetic diamonds are now color enhanced by a process that involves first HPHT annealing, then irradiation, followed by lowtemperature heating (likely in that order), to produce several colors, including red, pink, orange, and green (Schmetzer, 2004; Shigley et al., 2004; Wang et al., 2005a; Wang and Johnson, 2010b; Wang et al., 2010). Identification generally requires measurement in a laboratory of the absorption and/or photoluminescence spectral features present with the diamond cooled to a low temperature, although in some cases standard gemological testing can also offer clues (see e.g., Shigley, 2008). Other combinations also exist, such as irradiated and glass-filled diamonds (Gelb, 2005; Gelb and Hall, 2005).
Topaz.
The potential enforcement of Nuclear Regulatory Commission (NRC) guidelines on irradiated gems (American Gem Trade Association, 2007) caused great concern in the first decade of the 2000s. Since 1986, NRC regulations have stated that any neutron-irradiated gemstone produced in or imported into the U.S. must be tested for residual radiation by an NRC-licensed testing facility (Nuclear Regulatory Commission, 1986; Ashbaugh, 1988). Whereas considerable amounts of blue topaz were once treated in the U.S.—and then properly tested for radioactivity and held until the radioactivity subsided— nearly all treated blue topaz entering the market since the latter half of the decade has been irradiated and annealed in other countries, some of which may not restrict the export of “hot” material.
Amid the confusion generated by this issue, several major retail chains and department stores stopped selling blue topaz. After receiving numerous trade and public inquiries regarding blue topaz, the NRC issued a fact sheet on irradiated gemstones (United States Nuclear Regulatory Commission, 2008). To further address the issue, the Jewelers Vigilance Committee (JVC) and American Gem Trade Association (AGTA) published a 2008 brochure titled “The Essential Guide to the U.S. Trade in Irradiated Gemstones.”
To our knowledge, the NRC has still not enforced its regulations, and neutron-irradiated blue topaz continues to be imported and sold in the U.S. However, no blue topaz containing residual radioactivity has been reported recently in the trade.
Earlier—around 2000—Europe faced similar concerns that irradiated blue topaz exhibiting residual radioactivity had made its way into several different countries (Kennedy et al., 2000).
U.S. Postal Service Irradiation.
During the anthrax scare of late 2001, the USPS irradiated envelopes and packages to kill potential biological agents. The company that the postal service contracted with to perform the test, SureBeam, used a linear accelerator to create a beam of high-energy electrons. The potential impact of this exposure was immediately recognized, since the same ionizing radiation is routinely used to change the color in several types of gems. McClure et al. (2001) showed alarming evidence of several gems that had their color changed dramatically after being exposed in SureBeam’s facility to the same dosage as was used for the mail. The USPS subsequently abandoned these procedures, after determining that the time and money needed to sanitize all mail would be prohibitive.
Green Quartz.
In the latter part of the decade, an unusual amount of faceted green quartz suddenly appeared on the world market. Nearly all these gems—which originated from Rio Grande do Sul, Brazil—began as colorless to light yellow quartz that was subsequently irradiated to produce the green color (Kitawaki, 2006; Schultz-Güttler et al., 2008). Natural green quartz does exist but is extremely rare, and “greened quartz” (also known as prasiolite) is produced by heating certain types of amethyst. Irradiated green quartz shows a broad spectral absorption at 592–620 nm, while prasiolite exhibits a broad band centered at 720 nm. When examined under a Chelsea filter with incandescent light, irradiated green quartz appears red and prasiolite appears green (Schultz-Güttler et al., 2008; Henn and Schultz-Güttler, 2009).
Beryl.
In addition to the huge quantities of irradiated yellow beryl, which remains undetectable, irradiated yellowish green beryls were seen. Milisenda (2007a) reported absorption lines between 500 and 750 nm for the ordinary ray, which are also typically seen in artificially irradiated “Maxixe-type” beryls. Mili - senda (2007b) reported a beryl with “Maxixe-type” spectra that was offered for sale as a cat’s-eye scapolite but proved to be a blue irradiated cat’s-eye beryl.
Hiddenite.
Milisenda (2005a) reported on a parcel of intense green faceted spodumenes from Pakistan, offered for sale in Idar-Oberstein as hiddenite, that were artificially irradiated. The stones revealed a broad absorption band centered at 635 nm. As expected for this material, the color faded to the original pale pink within a few days.
Pearls.
The irradiation of pearls has been known for decades, and little has changed since 2000. The treatment is almost always associated with freshwater pearls or nuclei, since the radiation appears to alter the state of the trace element manganese found in these materials. Gray, silvery gray, and black colors have all been produced. In fact, pearls were one of the gems significantly altered by the U.S. postal service irradiation mentioned above. Detection remains a challenge in some cases, and research has continued on its identification (Liping and Zhonghui, 2002).
SURFACE COATING
As it has been for centuries, applying surface coatings to change the color of gems continues to be a common practice. Not only do gemologists need to be aware of high-tech coatings, we must also remember to look for older, simpler alterations. Diamonds. Just as Miles (1964) described decades ago, in 2003 Sheby reported seeing two slightly yellow diamonds that were coated with a blue material to improve the apparent color. Also as a recent reminder, Eaton-Magaña (2010) described a 1.5 ct diamond with a color equivalent to Fancy pink that revealed a nearly imperceptible trace of reddish material on a natural when viewed with the microscope. After cleaning, the diamond was graded Faint pink.
Sputter-coated optical thin films were originally developed in the 1940s to improve the optical performance of lenses. We continued to see similar coating technology used on diamonds in the 2000s. Evans et al. (2005) and Wang et al. (2006b) reported on faceted diamonds that were colored pink by sputter-coated thin films. A potentially new kind of diamond coating was described by Epelboym et al. (2006)—rather than using the fluoride coatings previously known, pink and orange-treated diamonds were suspected of being coated with a silica film doped with gold.
Shen et al. (2007) reported that the trade was submitting greater numbers of pink diamonds coated by calcium fluoride (CaF2) to the GIA Laboratory for grading and origin reports. They also described Serenity Technologies’ use of multiple micro-thin coatings of various compositions to produce a variety of colors on diamonds, including intense blue, green, yellow, and orange to pink to purple-pink (figure 21).
We continue to see crude yet effective colored coatings applied to the girdle facets of diamonds with permanent markers and solutions made from colored art pencils.
Diamond-Like Carbon Thin Films.
Super-hard coatings, such as diamond-like carbon (DLC) films, are becoming increasingly popular for a variety of mechanical, scientific, and technological applications, such as cutting tools, razor blades, and the like. This technology is also making its way into the gem industry. Several companies, including Serenity Technologies and Zirconmania, market DLC-coated cubic zirconia. Eaton-Magaña and Chadwick (2009) reported that these products were easily separated from diamond.
Serenity Technologies also offers a “patent pending nanocrystalline diamond coating process” named “Diamond Rx” which they apply to a variety of gems, including emerald, apatite, chrome diopside, zircon, peridot, tourmaline, kunzite, tanzanite and aquamarine (Serenity Technologies, 2010). They maintain that such coatings are extremely durable. However, it is very difficult (and sometimes impossible) to identify whether these DLC coatings are in fact even present on a gemstone.
Tanzanite.
In April 2008, a Los Angeles gem dealer encountered two parcels comprising a few hundred color-coated tanzanites (E. Caplan, pers. comm., 2010; figure 22). Research concluded that the smaller stones (4.5 mm) could be identified on the basis of unusually intense color for their size, by areas of wear seen with microscopic examination, and by unusual surface iridescence (“American Gemo - logical Laboratories identifies. . . ,” 2008; McClure and Shen, 2008). Larger stones (e.g., 3+ ct) were much more difficult to identify with magnification, but EDXRF and LA-ICP-MS analyses revealed Co, Zn, Sn, and Pb in the coating (McClure and Shen, 2008). Since their initial sighting, coated tanzanites have all but disappeared from the market.
Topaz.
In the late 1990s, we began to see different colors of topaz (blue-to-green, orange, pink, and red) that were being represented as “diffused” (Fenelle, 1999; McClure and Smith, 2000). Schmetzer (2006, 2008) reviewed the patent literature and concluded that the various mechanisms and treatment methods were not diffusion and should all be described as “surface coated.” However, Gabasch et al. (2008) showed that certain colors were due to coatings, whereas others were diffusion-induced. For more details, see the section on topaz under “Diffusion Treatment” above.
Coral.
Typically, gem coatings are ultra-thin. However, Hänni (2004) described black coral (also known as horn coral) that was coated with several relatively thick layers of artificial resin.
Pearls.
Any gem can be coated to alter its color, provide a degree of protection, improve the luster, or mask some imperfection. Pearls usually fall into the latter three categories. Porous by nature, pearls may be coated for protection from harmful chemicals. Or they may have luster and/or surface imperfections that a coating can hide. In this decade, a number of coatings were applied to natural and cultured pearls (Moses and Reinitz, 2000; Hurwit, 2002; Krzemnicki, 2005a; Shor, 2007). One development in particular that should be carefully monitored by the pearl industry in the future is the application of DLC coatings (Drucker, 2008) to improve durability.
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