Table of Contents
What is the key to making a gem the most beautiful it can be? The ancients thought a blend of art and science was needed to unlock gemstone beauty. Brilliance and fire, they said, lie hidden within gemstones and await the cutter's art to be released. That art consisted of shaping, faceting, and polishing. But there is more to gemstone beauty than the ability to glitter and glow. Gemstone beauty also consists of fine color and clear complexion. The ancients believed that science could help gems attain the finest color and appearance, and the enhancements that they developed remain essentially the same today--if not in practice, surely in principle. Put simply, enhancement allows the jewelry industry to use various forces of nature, like heat, to unlock the inherent beauty residing within a gem. In recent years, ancient gem-improvement technologies like heating have been used to produce gem colors in no other way possible. Most tanzanite, for example, comes from nature a rather drab brown. Once subjected to mild heating, however, these stones turn handsome shades of blue and violet. What's more, the science of gem beauty has advanced to the point where the jewelry trade can harness other forces of nature, such as irradiation, that the ancients had no way of tapping. In the case of diamond, irradiation produces colors so like those of nature that gemological testing is needed to tell the natural from the enhanced. In the case of topaz, irradiation produces colors far superior to topaz found in nature. Enhancements have been making gems beautiful for as long as people have been wearing them.
The American Gem Trade Association (AGTA) defines a gemstone enhancement as any process other than shaping, faceting, and polishing "that improves the appearance (i.e., the color, clarity, or phenomena), durability, value, or availability of a gemstone." The process covers a wide range of techniques, from traditional ones like oiling and heating to modern innovations like diffusion and irradiation. Depending on the method used and the gem that receives it, these enhancements can be long lasting and very stable or require special care and handling.
History of Gemstone Enhancements
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 biggest differences 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.
Another decade has passed since we reviewed the events of the 1990s as they pertain to gemstone enhancements and their detection (McClure and Smith, 2000). At that time, we observed the issue of disclosure (and, especially,the failure to disclose) had caused major upheaval in all areas of the jewelry industry. We ended that retrospective article by stating there would be no end to fresh challenges in treatment identification and disclosures as we entered the new millennium. There were treatments discovered that no one suspected were possible. There were crises of disclosure that resulted in televised exposés and unfavorable publicity for the industry. There were improvements in treatments developed in the 90s that made them more efficient and often harder to detect.
Detection methods have also become more complex. Gemological laboratories have had to invest in more sophisticated instrumentation, sometimes at a great expense. For the frontline laboratories, being a good gemologist is no longer good enough.You must also have training in the earth sciences and analytical instrumentation to function effectively in such an environment. Now more than ever, the gemologist in the trade must be able to recognize when a stone requires more advanced testing.
It is important to emphasize that many of these treatments can still be detected with standard gemological equipment, but staying current on the latest developments is absolutely essential. The knowledge base concerning treatments is constantly changing. Nearly every gem material (e.g., figure 1) is subject to treatments of one form or another. Building on previous reviews (Kammerling et al., 1990a; McClureand Smith, 2000; Smith and McClure, 2002), the aim of this article is to provide an overview of the treatments and identification challenges associated with them that were common during the first decade of the 2000s.
Nomenclature and Disclosure
Although there is no global standard regarding how a seller should disclose gem treatments or enhancements, there is a general agreement that they should be disclosed. This disclosure should be to all purchasers, at all levels of commerce(from miner to cutter, wholesaler, jewelry manufacturer, retailer, and ultimately the consumer).To find the proper protocol in your country or area, contact one of your national or regional colored stone and diamond organizations, such as AGTA (www.agta.org), ICA (www.gemstone.org),CIBJO (download.cibjo.org ), or the World Federationof Diamond Bourses (WFDB, www.wfdb.com). In the early 2000s, a group that came to be known as the Laboratory Manual Harmonisation Committee (LMHC) was formed at the request of leaders of the colored stone industry. Its purpose was to bring together representatives of many of the major gem laboratories and attempt to standardize wording on their reports (International labs. . . ,2000). The LMHC is autonomous and has representatives from the U.S., Switzerland, Thailand, Italy, and Japan. If agreement is reached on a given subject, they issue an information sheet with the wording that is expected to be seen on reports from those labs. Todate, 10 such information sheets have been issued, and the group continues to meet twice a year (to download these standardized nomenclature sheets, go to www.lmhc-gemology.org/index.html).
Gemstone Thermal Enhancement
For a wide variety of gem materials, heat treatment is still the most common enhancement. In some cases, heat treatments can still be identified by routine methods. In others, conclusive identification is possible only with advanced instrumentation and techniques. In other gems (e.g., aquamarine, citrine,amethyst, and tourmaline), heat treatment remains virtually unidentifiable by any currently known methods. For this last group of stones, which are heated to induce permanent changes to their color, this enhancement may be the rule rather than the exception. One should assume that most often those gem materials have been heated.
High-pressure, high-temperature (HPHT) treatment of diamonds was only introduced commercially in 1999, and much of the first decade of the 2000s was devoted to expanding this high-tech treatment to colored diamonds on the one hand and detecting it on the other. Research efforts thus far have provided methods to identify not only the lightening of color diamonds, but also the production of a wide variety of fancy colors.
Diamond Thermal Enhancement
The last decade bore witness to the greater presence of color-treated diamonds, with the global trade reportedly approaching 25,000 carats per month in the latter half of the decade (35% of the total diamond trade; Krawitz, 2007). Although not specifically noted, this figure probably refers mostly to irradiated and annealed diamonds of many different colors. Irradiation, heating, HPHT, or a combination of these treatments can create virtually every hue possible (figure 2), including black and colorless.
HPHT Treatment to Remove Color in Diamonds
HPHT treatment of diamonds to remove or induce color was a central topic of the diamond community throughout the 2000s. In 1999, General Electric Co. and Lazare Kaplan International announced the commercial application of an HPHT process for faceted diamonds(Pegasus Overseas Limited, 1999) that removed color from brown type IIa stones (by annealing out vacancy clusters associated with the brown color in plastically deformed diamonds; Fisher, 2009). Even though scientists had recognized these and other possibilities 30 years earlier (see, e.g., Overton and Shigley, 2008), the ability to transform a type IIa brown diamond to a colorless stone was a surprise (see, e.g.,Smith et al., 2000). After HPHT treatment, the majority of these diamonds received D through G color grades, and the results were permanent (Moseset al., 1999). Gemological researchers globally mobilized to understand and identify the process (e.g.,Chalain et al., 1999, 2000; Schmetzer, 1999; Collinset al., 2000; Fisher and Spits, 2000; Smith et al.,2000).
By late 2000, more than 2,000 decolorized type IIa HPHT-treated diamonds had been seen at the GIA Laboratory (McClure and Smith, 2000). Today, with several treaters in various countries removing color from diamonds with HPHT annealing, this treatment has become almost commonplace.
Determining diamond type is central to the detection of colorless to near-colorless HPHT-treated diamonds. For a thorough review of how diamond type is determined, see Breeding and Shigley (2009). Nearly 99% of all natural gem diamonds are type Ia.Thus far, all colorless to near-colorless HPHT-treated diamonds reported in the literature have been type IIa. Fortunately, it is easy to determine if a diamond is not a type IIa by using the Diamond Sure(Wel bourn et al., 1996), SSEF Type II Diamond Spotter (Boehm, 2002; Hänni, 2002), or other simple gemological methods (Breeding and Shigley, 2009). At the present time, if a colorless to near-colorless diamond is not type IIa, then it is not HPHT treated.
Visual features related to damage caused by the extreme conditions of the treatment may be seen in some colorless to near-colorless HPHT-treated diamonds. These include a frosted appearance caused by etching or pitting, as well as gray or black graphitization. Such features are not commonly observed in untreated colorless type IIa diamonds, although lightly pitted surfaces and graphitized or graphite inclusions have been seen on rare occasions. Therefore, such features are a good indication of treatment, but they are not proof by themselves (Moses et al., 1999;McClure and Smith, 2000; Gelb and Hall, 2002).Because these heat damage related features are not always present in a faceted diamond or may be difficult to discern, detection of HPHT treatment in a type IIa diamond generally requires measurement of the absorption and/or photoluminescence (PL) spectra taken with the diamond cooled to a low temperature (see Chalain et al., 1999, 2000; Collins et al.,2000; De Weerdt and Van Royen, 2000; Fisher and Spits, 2000; Hänni et al., 2000; Smith et al., 2000;Collins, 2001, 2003; Novikov et al., 2003; and Newton, 2006).
HPHT Treatment to Produce Color in Diamonds
Refinements to HPHT processing has yielded commercial production of a variety of colors in both type I (orangy yellow, yellow, yellow green) and type II (pink or blue) diamonds (Shigley, 2008; see, e.g., figure 3).
Identifying HPHT-treated type Ia diamonds requires both IR and low-temperature visible-range spectroscopy, but several gemological properties offer evidence (see Reinitz et al., 2000). The pink and blue HPHT-treated diamonds initially examined by Hall and Moses (2000, 2001b) ranged from Faint and Very Light to Fancy Intense and Fancy Deep. Low temperature PL spectra identified these products. As discussed below, combining treatments (e.g., HPHT annealing, irradiation, then low-temperature heating) can produce interesting results, such as intense pink-to-red diamonds (Wang et al., 2005b). Smith et al. (2008a,b) contributed useful charts for identifying the natural or treated origin of color in pink and blue diamonds.
Heat-Treated Black Diamond
In the late 1990s, it became popular to pavé-set small natural-color blackdiamonds alongside colorless diamonds in jewelry(Federman, 1999; Gruosi, 1999; Misiorowski, 2000). This design trend continued into the 2000s. As is often the case with successful jewelry lines, less expensive approaches soon followed. Harris and Vance (1972) had experimented with the production of artificial graphitization in diamond, which Halland Moses (2001a) confirmed by heating a sample under vacuum for a few minutes to several hours and turning it black; Raman spectra showed a pattern that matched graphite. Notari (2002) discussed several different commercially practiced methods of heating to produce graphitization and black coloration in diamonds.
In many cases, microscopic examination with fiber-optic illumination can provide proof of heat treatment in black diamonds because the black (graphitized) areas are largely confined to surface-reaching cleavages and fractures (Hall and Moses, 2001a). In unnatural-color black diamonds, the graphitization is randomly dispersed throughout, referred to as a salt and pepper effect (Kammerling et al., 1990b). This random orientation is also seen in other color-causing inclusions in natural-color black diamonds, such as magnetite, hematite, and native iron (Titkov etal., 2003). This determination, however, requires age mologist experience in examining known samples of both natural-color and heat-treated black diamonds(see, e.g., Smith et al., 2008c).
Ruby and Sapphire Heat Treatment
As in the preceding two decades, the heat treatment of corundum to substantially change its color remained a troublesome issue. Heating was applied to the vast majority of rubies and all colors of sapphires during the 2000s. In some cases, clarity was also affected, as with the flux-assisted healing of fractures (in combination with high-temperature heat treatment) that began in the early 1990s with the discovery of huge quantities of ruby at Mong Hsu, Myanmar (see Peretti et al.,1995; figure 4). The 2000s ushered in a greater understanding of this material, which dominated the ruby market and cooperation between gemological laboratories to adopt standardized wording to describe heat treatment in corundum and, most importantly, the degree to which fracture healing has occurred and the amount of solidified flux residue (see e.g.,www.lmhc-gemology.org/index.html). Today, there is less production of ruby at Mong Hsu, but this technique is now being used on rubies from Africa (Shorand Weldon, 2009).
There were also new areas of concern, such as beryllium diffusion with high heat (see DiffusionTreatment below) and the Punsiri high-temperature treatment for blue sapphires. With regard to the latter, concerns arose in late 2003 when some laboratories first observed unusual color concentrations in larger heat-treated blue sapphires (figure 5) immersed in methylene iodide (Scarratt, 2004; Smith et al.,2004). All had one consistent characteristic: a colorless or near-colorless outer rim and a deep blue (or, if color change, purple) interior (figure 6).
After comprehensive analytical research (and GIAand AGTA observation of the technique as performed by treater Tennakoon Punsiri in Sri Lanka), the SSEF, AGTA, and GIA laboratories all came to the same conclusion: these stones were not diffused with beryllium or any other element (McClure, 2003b;Hänni et al., 2004; ICA issues its first lab report. . . ,2004). The major gem labs continue to identify sapphires treated by the Punsiri method as natural sapphires that show evidence of heat treatment.
Beginning mid-decade, demand and scarcity significantly drove up prices for colorless or white sapphire. As a result, dealers in Sri Lanka reported that lightly colored sapphires had been heated to render them colorless (Robertson, 2008). Ironically, the scarcity of natural white sapphire was caused in part by the large quantities that were being used for Tiblue diffusion and, to a lesser extent, Cr red diffusion.
Since the two previous G&G retrospective articles on treatments (Kammerling et al., 1990a; McClure and Smith, 2000), heat-treatment technology in the form of electric furnaces with precise temperature and atmospheric controls has become more sophisticated and accessible. During the 1980s and 1990s, nearly all commercial corundum heat treatment was being conducted in Thailand. While Thailand remains important, Sri Lanka is now a major force. Other effective corundum-heating capabilities exist in other producing regions such as Africa, Myanmar, China, and the U.S. (Montana). Nevertheless, some pink sapphires and rubies continue to be heated using simple blow pipe methods at mine sites and trading centers inVietnam, Sri Lanka, and elsewhere (R. Hughes, pers.comm., 2010).
Heat treatment, particularly at high temperatures,can dramatically alter the internal characteristics and properties of sapphires and rubies. During the past decade, a number of articles addressed heat-treatment techniques and their effects on gem corundum from localities such as Madagascar (Wang et al., 2006a), Montana (Schmetzer and Schwarz, 2007; Kane, 2008), Australia (Maxwell, 2002), Vietnam (Winotai et al.,2004), Myanmar (Kyi et al., 1999), and Malawi(Rankin, 2002; Rankin and Edwards, 2003). Schmetzer and Schwarz (2005) discussed the identification of natural, heated, and Be-diffused yellow to reddish orange sapphires from Sri Lanka, Montana, Madagascar, and Tanzania. David and Fritsch (2001) contributed a valuable study on the use of infrared spectra to distinguish heated rubies and sapphires from 20 different geographic origins.
Proof that a ruby or sapphire has been heat treated is sometimes readily apparent, but in many cases it requires considerable knowledge and observational skills. The criteria for identifying heat treatment in rubies and sapphires using a microscope were set forth during the 1980s and 90s (for a summary, seeKammerling et al., 1990a). They include stress fractures surrounding melted or heat altered inclusions; spotty coloration in blue stones, best seen with diffused illumination; colored halos surrounding altered solid mineral inclusions; stubby, partially absorbed (dot-like) silk; and pockmarked, resorbed facets.
Relatively low-temperature heating (i.e.,8001200°C), particularly of purplish pink sapphires (and some purplish red rubies) to remove the blue color component, is still very difficult to detect with standard microscopic testing. The lower the temperature used, the more difficult the detection will be (Krzemnicki, 2010).
Amber Thermal Enhancement
Amber and copal are still heated to improve clarity, color, and hardness, and to induce sun spangles (Kammerling et al., 1990a; O'Donoghue, 2006). In 2009, Abduriyim et al. described a new method to produce a green color in amber and copal (figure 7),some as bright and green as peridot, using a two stage process of controlled heat and pressure in an autoclave for long durations. Multiple treatments may increase the color saturation, producing an intense, pure green hue that has not been seen in untreated amber. The treatment also reportedly hardens the amber, making it more stable (Abduri -yim et al., 2009). While infrared spectroscopy can distinguish amber from copal (Guiliano et al., 2007), this new treatment process ages the copal, rendering its properties similar to those of amber and making its identification as copal extremely difficult, even with advanced analytical methods.
The presence of a small absorption around 820cm in the FTIR spectra confirmed the use of multiple treatments on all the commercial green amber samples tested by Abduriyim et al. (2009). Although the use of heat treatment on a specific piece can be ascertained, whether or not the original starting material was copal or amber still cannot be routinely identified.
Garnet Thermal Enhancement
Around 2003, members of the trade began reporting that Russian demantoid is routinely subjected to low-temperature heat treatment to remove or reduce the brown color component (The reds. . . ,2003; N. Kuznetsov, pers. comm., 2003). Other than the presence of altered inclusions in some stones, no measurable gemological means of detection has yet been reported. The result is that some international laboratories make no determination of whether a demantoid has been heated, whereas others will state if indications of heating are present (Pala International, 2010).
Spinel Thermal Enhancement
As was the case with garnet, it was long believed that spinel was never treated. Beginning in 2005, however, researchers determined that certain pink-to-red spinels from Tanzania were heat treated (Saeseaw et al., 2009a). In 2007, four large (654 kg) spinel crystals were faceted into many thousands of fine gems from melee sizes up to 1050 ct (Pardieuet al., 2008). Again, rumors of heated spinel began to circulate prompting researchers to conduct before-and-after heat treatment studies of spinel from various localities. It was concluded that heated and unheated natural spinel could easily be distinguished by the width of the 405 cm1 Raman line, or by examining the width of the Cr3+ PL spectrum line in stones containing sufficient chromium (Saeseawet al., 2009b,c; Kondo et al, 2010).
Tourmaline Thermal Enhancement
The heat treatment of Cu-bearing tourmalines from Paraíba, Brazil, and the enormous demand for both the natural-color and heat-treated material, continued through the decade. An interesting twist occurred when Cu-bearing tourmalines were discovered in Nigeria (Smith et al, 2001; Breeding et al, 2007) and Mozambique (Abduriyimand Kitawaki, 2005; Abduriyim et al., 2006; Laurs et al, 2008).
These tourmalines were commonly heated (e.g.,figure 8) to create a wide range of attractive colors similar to many of those found in Paraíba. With the exception of obviously heat-altered inclusions, standard testing cannot identify heat treatment in these tourmalines.
For several decades, heat has been known to reduce saturation in overdark red tourmalines. However, many cutters resist heating these stones because tiny fluid inclusions tend to burst during heating and cause breakage (B. Barker, pers. Comm., 2008).
Zircon Thermal Enhancement
Faceted orangy, pinkish, and yellowish brown zircons from Tanzania, known by trade names such as cinnamon zircon, were plentiful in the market (see figure 1, no. 10). To lighten overly dark tones, nearly all such stones in the market have been heated in a test tube with low heat (R. Shah, pers. comm., 2010). Since there is no means of identifying whether these gems like blue zircon have been heated, we recommend that all zircons of this color range be considered as heated.
Cultured Pearl Thermal Enhancement
Although not widely recognized, heat is sometimes used to alter the appearance of cultured pearls. Heat alone usually produces more saturated yellow colors, and other effects can result when heat is used in combination with other methods (better techniques improve brown pearls, 2006) such as bleaching. In all cases, detecting heat treatment can be challenging. There are no obvious thermally enhanced inclusions as in some gems, and the only useful methods determined to date usually involve UV fluorescence reactions and UV-Vis-NIRspectroscopy (Elen, 2001; Wade, 2002).
Gemstone Diffusion Treatment
Diffusion treatment was more problematic for colored stones than any other enhancement in the 2000s. Beryllium diffusion, in particular, upped the bar on the sophistication of equipment and level of knowledge needed by gem laboratories.
Corundum Diffusion Treatment
Chromium diffusion of corundum has been debated as being more of a chemical reaction at the surface of the stone than true diffusion. It was actually shown on some stones to be a synthetic ruby overgrowth (Smith, 2002). This treatment is very difficult to perform, and to the authors knowledge is not currently being used.
The diffusion of corundum using cobalt was also reported in the last decade (Kennedy, 2001; McClure, 2002b), but this material was easily identified with magnification and diffused light by a very shallow color layer that showed spotty coloration, as well as observation of a cobalt spectrum with a desk-model spectroscope.
The first serious diffusion challenge started in 2001, when large numbers of pinkish orange (padparadscha) sapphires showed up in certain markets (Genis, 2003). The color was attributed to a new form of heat treatment done in Thailand. Some labs in Japan are said to have issued over 25,000 reports stating just that (Genis, 2003; Weldon, 2003). In early 2002, however, examination with the stones immersed in methylene iodide revealed that they had a surface conformal layer of orange color surrounding a pink core (Weldon, 2002;figure 9). With this discovery, the illusion that the color was caused by standard heat treatment began to crumble (Orange crush, 2002).
The story is well documented by Emmett et al (2003). At first, the reason for the orange surface related color zone could not be determined. The standard equipment available in gemological laboratories detected nothing unusual (McClure et al,2002). At the February 2002 Tucson shows, however, it was announced that the culprit was beryllium (GIA-GTL suspects beryllium causes orange color in treated pink sapphires, 2002; Hughes, 2002; Genis, 2003). Unfortunately, beryllium was almost unknown in corundum, with very little information available in the literature.
There were two major differences between Ti and Be diffusion. First, beryllium, being a very small atom, was capable of diffusing all the way through even large sapphires. Titanium could not do this, even with heating times lasting several weeks. Second, titanium is only capable of creating blue color in sapphire. Beryllium, however, can affect virtually every color of corundum in some way when combined with Fe (figure 10). Colorless, light yellow, or light blue can be turned to intense yellow (see, e.g., figure 11); pink can be altered to orange or padparadscha color; dark brownish red to bright red; and dark inky blue to lighter blue just to name some of the possibilities (Coldham, 2002; Henricus, 2002;Moses et al, 2002).
Identifying this treatment turned out to be complicated. Severely heat-damaged inclusions were found in many of these treated stones (Roskin, 2003a; Schmetzer and Schwarz, 2005), but they only indicate that the stone was treated at extreme temperatures and they do not prove the presence of Be(Emmett et al., 2003). After a time, we started to see Be-diffused blue sapphires treated by an even newer method that showed no surface-related characteristics and created unusual inclusions (figure 12; Choudhary, 2006; Kitawaki and Abduriyim, 2006; Roskin, 2006; DuToit et al., 2009). These inclusions also did not prove Be treatment, but they strongly indicated that further testing was needed.
Areas of synthetic corundum overgrowth were commonly seen on Be-diffused faceted stones, but Be was not necessary for this to happen (McClure, 2002a). UV fluorescence was helpful in some situations, but not all (Fritsch et al, 2003). Even chemical analysis was a problem, as the standard instruments used at gemological laboratories and most universities(EDXRF and electron microprobe) cannot detect light elements such as beryllium. Detecting Be meant using instrumentation such as mass spectrometers. At that time, no gemological laboratory possessed this capability, so testing had to be done at commercial laboratories, which is very expensive. Today, several gem labs have this equipment in house and offer Be testing as a service.
Feldspar Diffusion Treatment
In 2002, a transparent red feldspar colored by copper debuted on the market, reportedly originating from the Congo. This did not raise suspicion initially, as natural red feldspar colored by copper was already well known (from Oregon). Over time, however, the supposed location of this feldspar mine kept changing to China, Inner Mongolia, and Tibet. Although most of the feldspar was red,some green material also entered the market (e.g., figure 13).
The first question raised about this material had nothing to do with treatment, but focused on nomenclature (Krzemnicki, 2004a): Was it labradorite or could it be called andesine? Andesine was rare in gem quality, so this could be very valuable to marketing efforts. Although much of the material was indeed andesine, in time this became a secondary issue. Large amounts of this feldspar were being sold as all-natural, untreated material. In July 2008, however, Masashi Furuya of the Japan Germany Gemmo logical Laboratory reported that he had direct evidence (from experiments done in Thailand) that this feldspar was being diffusion treated by a three-step process that took months to complete (Furuya, 2008). He also mentioned the same type of material being diffused in China by an unknown process.
Other reports suggested that the unusual color zoning found in this material indicated diffusion treatment (Fritsch et al, 2008). Subsequent studies conflicted with this idea, showing natural Oregon material with very similar zoning (McClure, 2009).
To address the controversy, systematic experiments were undertaken to diffusion treat plagioclase.They showed it was surprisingly easy to duplicate the Cu-diffusion process in only a few days(Roskin, 2008; Emmett and Douthit, 2009). Also, gemologists visited a mine in China’s Inner Mongolia that produced andesine-labradorite, but only with a pale yellow color (Abduriyim, 2008). The material could not be simply heated to red or green because it contained virtually no copper (Thiran -goon, 2009). This fact left diffusion as the only possible treatment method for these stones.
Claims of a mine in Tibet began in 2005, but their credibility was questionable. In 2008, a team visited a mine in Tibet, collected samples, witnessed mining, and documented red andesine that appeared to be in situ (Abduriyim, 2008). However, the samples collected proved to be virtually identical to the diffused Inner Mongolian red andesine, calling the mine into question again. Its authenticity is still not resolved. With the controversy surrounding this material, identification of this feldspar as treated is still problematic using standard gemological techniques, primarily because the issue of the Tibet mine is not resolved. One technique that may have helped identify feldspar is the color zoning technique. A complete bulls-eye color zoning with red-inside-green usually means the stone is natural, while green-insiders may indicate treatment (McClure, 2009). However, if you have a partial bulls-eye or merely zoned areas, this criterion is unreliable. To date, larger platelets of copper have been found only in the natural Oregon material (McClure, 2009; Rossman,2009, 2010). However, separation of Oregon and Chinese feldspar in a gemological laboratory is not difficult as they are all distinct chemically.
Topaz Diffusion Treatment
Blue-to-green topaz surface-treated with cobalt was marketed in the 2000s as an alternative to irradiated blue topaz (Federman, 2007a), a tactic that took advantage of the public’s fear of radiation. This material has long been marked as diffusion treated, even though this claim was never truly substantiated (Gabasch et al. 2008). determined that the layer of coloration was diffusion induced, creating new phases at the surface. This is not so different from the opinions put forth in the late 90s that the treatment was more of a chemical reaction than diffusion.
Several companies announced lines of diffusion treated topaz in new colors of red and pink to champagne and bicolors (Roskin, 2003b; Diffused topaz from India, 2003), but questions still exist as to whether they are from a diffusion or coating process. Identification of this material is fairly easy. With magnification, the color has a spotty appearance and, due to the extremely thin nature of the color layer, any small chips or abrasions will show the colorless nature of the base topaz.
The discovery that diffusion treatment of feldspar was possible generated claims that many other gems such as Cu-bearing tourmaline from Mozambique, Imperial topaz, and tsavorite(Federman, 2009) were also being diffusion treated. To date, no significant scientific data has been presented to support these claims, even though experiments have begun to explore some of these possibilities (Saeseaw et al., 2009a).
There was one report of tanzanite possibly being diffused, but examination of the suspect stones showed no evidence of diffusion (Wang, 2003).
Clarity Enhancement of Gemstones
During the 1990s, clarity enhancement was one of the jewelry trades most formidable challenges. Clarity enhancement is mainly used with emeralds. Unfortunately the wide knowledge of this trade secret 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 have changed and the focus has been on different gem materials.
Clarity Enhancement in Diamonds
The biggest concern about the clarity enhancement of diamonds is 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).
Laser drilling and bleaching is a permanent and stable process that results in an improvement in the apparent clarity of a diamond. 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. This new version took advantage of advances in laser technology developed in Israel and is referred to as the KM treatment (short for kiduah meyuhad, or special drillin Hebrew; Horikawa, 2001). This method did not actually drill a hole into the stones, but 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 (figure15; 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.
Other observations were posted in the literature periodically. Among them were changes in flash effect colors (Cracco and Johnson, 2008), filled fracturesin 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 Clarity Enhancement
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; Rockwelland 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 led to huge amounts of treated rubies being sold at very low prices.
Identification of these filled rubies was not difficult. Most had so many filled fractures that the flasheffect 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).
However, 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 three tiered 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; figure19). The other labs of the LMHC adopted these criteria, as well. American Gemological Laboratories (AGL) and the International Colored Gemstone Association (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 inclosed-back mountings (Krzemnicki, 2007), and estate jewelry (Quinn Darenius, 2010).
Emerald Clarity Enhancement
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 which led to 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 three or 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 it’s 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.
Gemstone Irradiation and Combined Treatments
Irradiation is a modern gemstone treatment, but it is also perhaps the oldest, naturally-occurring gem treatment. This is because there are natural sources of radiation in the earth. Many of these sources emit extremely low levels of radiation, but when a stone is exposed to these sources of radiation for millions of years, the cumulative effect can be great. Irradiation is the bombardment of a material with various subatomic particles. This treatment can occur naturally, or it can be done artificially in a lab, a nuclear reactor or treatment facility. The effect is the similar, and, in many cases, there is no way of knowing if the original source of radiation was the earth or the laboratory. The artificial irradiation of gems is done to create or alter colors. Colors are created by adding or subtracting electrons within the crystal lattice, causing it to interact differently with the light, which we see as a change in perceived color. This can be a subtle to strong increase in color, or an entire change of hue. For radiation to have an effect on color, the atomic conditions must be right. Not all materials can be affected by radiation and most are not.
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 over stones, 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 Irradiation Treatment
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 a 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 pressure)to produce a wide variety of colors including 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 low-temperature 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.g., Shigley, 2008). Other combinations also exist,such as irradiated and glass-filled diamonds (Gelb, 2005; Gelb and Hall, 2005).
Topaz Irradiation Treatment
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 GemTrade 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 radio activity 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 the SureBeams 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 Irradiation Treatment
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 592620 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 andSchultz-Güttler, 2009).
Beryl Irradiation Treatment
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 cats-eye scapolite, but proved to be a blue irradiated cats-eye beryl.
Hiddenite Irradiation Treatment
Milisenda (2005a) reported on a parcel of intense green faceted spodumene 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.
Pearl Irradiation Treatment
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).
Other Irradiation Effects on Gemstones
After treatment, some gems are ready to sell, such as tourmaline and smoky quartz. Others, like blue topaz and diamonds, need an annealing process (usually heat) to stabilize the color. Some materials will not be stable, even with annealing. These materials are typically Maxixe beryl, certain types of topaz (rhyolitic) and kunzite. Some materials, after radiation, will revert at various rates to its original color or even become colorless if over-heated. Most irradiated gems sold are stable. Kunzite is one stone that is known to fade whether irradiated or not. Some materials react better to different types of radiation. Diamonds and London Blue topaz are treated in cyclotrons or linear accelerators. These require annealing, as well as a cool-down period of weeks to months, until they stabilize and no longer emit radioactive particles.
Gemstone Surface Coating
Coating is a method of gemstone enhancement that can vary widely. It can be as simple as a spot from a permanent marking pen on a diamonds girdle to nail polish on the underside of a stone. These are not recommended treatments, but they have been encountered in the jewelry industry. Most of us are familiar with foil-backs, which are usually glass with a foil backing to make the material more brilliant. These were common in older fashion jewelry. Centuries ago, this technique was used on natural gems to enhance color and brilliance, but this is not a common practice today, as we have better materials to work with. A small spot of color, applied with ink or under a prong, can enhance or diminish a stones apparent color and, therefore, its value. While most coatings are easily detected if you know what to look for, they can remain an effective deception because these types of treatment are not always checked.
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.
Modern gem coatings are similar to the films used for eyeglasses and camera lenses. Coatings are applied in a very thin layer and do not adversely affect the optic properties of the gem. Some older methods of coating remain that are performed on beads and less expensive materials. Most of these older treatments are not recommended as they can easily wear off the material. Chemical vapor deposition (CVD) is the preferred method of applying coatings today. This process applies extremely small particles on a surface to form a thin, bonded layer or coating. There is commonly a bonding layer applied first, then the layer that adds the color or optical effect is added on top of the bonding layer. It is similar to car painting, but on a nanoparticle scale. The coatings can add color, such as the CVD pink topaz, or create a metallic film, such as mystic topaz. They can also create a variety of fancy colors in diamond. This technique is also used to mask a color that is less desirable. Applying a light blue coating to a diamond can improve the apparent color of a slightly yellow stone. Coatings of this nature can be applied to many materials and be of any color or combination of colors. In most cases, the CVD coating is applied to the underside (pavilion) of a stone. This creates the desired effect, as well as protects the coating from damage when worn in jewelry. Most coatings will tolerate gentle care and handling, but some can be removed by ultrasonic cleaning. All coatings can be scratched off, but CVD process coatings are more durable. All coated gems require special care, in order to avoid damage to the coating. If closely observed, it is sometimes possible to detect a coating by its iridescent effect in reflected light, or in some cases, it is possible to see where the coating may have worn off. JTV carries only the more-durable, CVD coating process on its colored topaz and quartz.
Diamond Surface Coating
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 when viewed with the microscope. After cleaning, the diamond was graded Faintpink.
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 (figure21). 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 diamonds.
Serenity Technologies also offers a patent pending nanocrystalline diamond coating process, 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 Surface Coating
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; McClureand 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 tanzanite shave all but disappeared from the market.
Topaz Surface Coating
In the late 1990s, we began to see different colors of topaz (blue-to-green, orange, pink, and red) 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 Surface Coating
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.
Pearl Surface Coating
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 may 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.
Other Gemstone Coating Methods
Coatings allow for a wide range of colors and effects to be applied to natural stone materials. Colorless topaz can be coated blue to resemble blue topaz that is typically irradiated, and colorless quartz can be coated purple to resemble amethyst, but most often coatings create new colors and effects that cannot be found in nature. The future of this technology is looking at applying diamond coatings to gem materials in the hope of adding the hardness of diamond to the beauty and affordability of other gemstones. Although there is not yet a means detectable with gemological instruments that changes any measurable properties of the coated gem, the research continues. Lacquering is the process of applying a clear outer layer to a material. A gem material may be dipped into, sprayed or painted with a clear coating. This treatment is commonly applied to shell and wood as well as some softer bead materials in order to protect them and prevent the absorption of oils or fluids that may cause discoloration.
Dyeing is the oldest and most common color enhancement. Many chalcedonies are seen in vibrant greens and blues, dyed by methods that have been used for hundreds of years. These dyes can vary greatly from organic or vegetable dyes to chemical salts and natural pigments. Some treated gems are obviously artificial in their appearance, but others convincingly imitate the natural colors found in nature. Some dyes may be rinsed away, or fade with time or exposure to light. The best methods of dyeing are permanent and stable. There is rarely just one method of dyeing for a given stone, but it will vary by source, vendor and the technologies available at the time. Dyeing gemstones may be simple in concept, but the details will vary greatly. Some stones may be simply soaked at room temperature for an extended period until the dye slowly seeps into the material. Pearls are often dyed in this way or with low heat. Natural pigments, chemical salts and heat may speed the process or yield more permanent results. Dyes will often vary in their degree of penetration from just the surface to deep within a gem, so re-polishing is not recommended on most dyed gems. Care must be taken when cleaning such gems, as dyes can sometimes be removed. Dyes must always be disclosed, as all are not permanent and they can greatly affect the apparent quality and value. Examples of stones that undergo such treatment are the quench-crackled and dyed quartz. The quench crackling allows the dye to enter and color the quartz. The process also creates fissures which help make a convincing emerald imitation. Without the cracks, the dye could not penetrate the quartz. Howlite, a whitish variety of quartzite, is also commonly dyed. The white body color and porosity of the material allow for ideal dyeing conditions. It is quite common for jades to be colored with traditional vegetable dyes and this is often combined with a polymer treatment (B-Jade). Coral is commonly dyed to look like its rarer salmon to red colors. Even expensive gems like emerald, ruby and sapphire, if they have fissures, can have colored oils added to improve appearance. While many of these treatments have been done for centuries, it is important to disclose the presence of dyes and the durability of the added color.
History of Dyeing
Although it dates back to the time of Pliny (2379 AD), dyeing continues to be seen in nearly every gem material that is porous or has surface-reaching fractures. Careful microscopic examination will frequently reveal the presence of dye in cracks and around grain boundaries. In a number of porous materials, rubbing the surface with a cotton swab soaked in acetone or a 10% hydrochloric acid solution can identify the presence of dye. In others, absorption spectra can provide proof of dyeing.
Dye continues to be used to improve the appearance of lower-quality natural and cultured pearls(Wentzell, 2005). While the majority of dyed pearls are nacreous, dye may also be used to make non nacreous pearl imitations more convincing, such as those mimicking Melo pearls (Wentzell, 2006). Of ongoing concern since the late 1990s is the detection of dyed golden cultured pearls (figure 23;Concerns raised. . . , 2003; Liu and Liping, 2007). Some samples present identification challenges, requiring the use of chemical analysis to detect trace elements such as iodine. Other developments involve the use of additional whitening compounds in freshwater non-beaded cultured pearls (Shouguoand Lingyun, 2001) and the use of metallic dyes injected into pearl sacs (Pre-harvest colour-treatedAkoya unveiled, 2008; Coeroli, 2010). A form of dyeing marketed as lasering has also been reported. This is said to produce dark peacock green or dark purple colors (Liping, 2002).
Other Dyed Gem Materials
Several other dyed gem materials were encountered during the decade. Blue and green diamond crystals were found to owe their color to dyeing (Van der Bogert, 2005). Quartzite was dyed red to imitate ruby (Mayerson, 2003a), whereas green dye was found in quartzite to resemble emerald (Milisenda, 2003). Mayerson (2003b) described an effective simulant for high-quality jadeite: a tricolored(lavender, green, and orange) dyed and polymer impregnated quartzite bangle bracelet. Tan et al.(2006) used light-induced auto fluorescence spectroscopy to identify dyed polymer-impregnated jadeite. Of particular interest was dyed jadeite found to resemble nephrite jade (Mayerson, 2004).
Low-quality red and blue corundum were found to have been dyed (Milisenda, 2004). A parcel of faceted rubies purchased in Afghanistan was identified by Milisenda (2005b) as dyed sillimanite. Dyed blue carbonate minerals, such as magnesite and dolomite, were sold as turquoise (Some dyed minerals.. . , 2000). To imitate common opal from the Peruvian Andes, marble was dyed pink and fashioned into beads (Milisenda, 2006). Raman and IR spectra identified dyed black chalcedony in an attractive pendant set with diamonds and pearls (DeGhionno and Owens, 2003). A copper-based dye was detected with UV-Vis-NIR spectroscopy in a natural-appearing chalcedony bead (Inns, 2007a).
Sugar and smoke do not sound like typical dyes, but they are used to dye some types of opal and chalcedony. These types of color enhancements are sometimes referred to as staining, as they do not use what are traditional dyes. Matrix opal, which is composed of grains of opal within a host rock, can have porous, non-opal areas. These areas, when blackened, can greatly enhance the fire of the opal by providing a dark contrast. By soaking the material in a solution of sugar, then subjecting it to acids (which does not hurt the opal), all but the carbon element in the sugar is removed. This creates a dark, black background. The result is a darkened outer layer against which the opals play of color is more dramatic. The darkened layer is usually just a few millimeters thick and can be polished or chipped off the stone. Black onyx, a type of chalcedony, is also treated in this manner, but the penetration is usually quite deep, often throughout the material. In the process of smoke treatment, hydrophane opal is exposed to concentrated smoke, gradually darkening the body color as it permeates inside the opal. Tea is commonly used to give an aged look to ivory and bone. The material is simply soaked in a strong tea until the desired result is reached.
The Process of Bleaching Gemstones
Bleaching is also a color enhancement; however, it removes color rather than adding it. Gems that are commonly bleached include pearls, ivories and corals. In many cases, a mild hydrogen peroxide formula is all that is needed to even the color and make a material appear whiter. Bleaching may be applied before dyeing to even out a gemstones color, so that dyes may be applied more uniformly. Some tigers eye is soaked in a mild chlorine bleach to lighten the color. These bleaching treatments are stable and permanent. Gemstone bleaching is a process that uses agents such as acids or hydrogen peroxide to remove unwanted color from a gem. Only a limited number of materials will respond to such treatment.
Jadeite with brown staining caused by natural iron compounds is often bleached with acid. This treatment started in the 1990s and was categorized in the impregnation section of McClure and Smith (2000) because jadeite treated in this manner must be impregnated with polymers, as the acid damages the structure, making it very susceptible to breakage.
This treatment has become commonplace in the jadeite market. However, the bleaching itself typically cannot be detected, only the polymers used for impregnation (Sun, 2001; Fan et al, 2007). The treatment is now being used on nephrite jade as well(Jianjun, 2005).
Bleaching is considered an acceptable pearl treatment due to the difficulty of proving a pearls exposure to chemicals such as hydrogen peroxide. All types of pearls are routinely bleached: natural, bead cultured, and non-bead cultured. Akoya cultured pearls continue to be routinely bleached and pinked (Roskin, 2002b). Bleaching is also known to be a major component of the proprietary process used to produce the chocolate cultured pearls (figure24) that entered the market during the decade(Zachovay, 2005; Hänni, 2006b; Wang et al., 2006c; Federman, 2007c)
Impregnation of aggregate stones and other porous materials was seen more often in the first decade of the 2000s. This is largely due to increased demand for inexpensive stones, a phenomenon primarily driven by television shopping networks. The practice now extends to some unusual materials as well. A number of the gems were only usable in jewelry when they were treated by impregnation (often referred to as “stabilization”).
The polymer impregnation of jadeite following the bleaching process described above was common during the last decade and will likely remain so in the future. At least one new analytical method was reported to detect this treatment (Liu et al,2009), but it's identification is still usually done with IR spectroscopy.
Nephrite was reported to have been polymer impregnated after bleaching with the intent of imitating “Hetian white” nephrite (Jianjun, 2005). It, too, can be positively identified by IR spectroscopy.
The greater demand for turquoise (a favorite of TV shopping networks) led to the use of more low-quality impregnated material. Sometimes the treatment is so extensive that the material is actually a composite (figure 25), and gemological properties such as SG and RI no longer match turquoise(Choudhary, 2010; McClure and Owens, 2010). Materials used for impregnating turquoise include wax and hardened polymers. A UV-hardened polymer was identified as a filler for the first time using Ramanspectroscopy (Moe et al., 2007).
Identification of this treatment is still mostly accomplished via IR spectroscopy (Henn and Milisenda, 2005; Chen et al, 2006), although many examples show veins and cavities filled with polymers that are visible with magnification.
Late in the decade, a product marketed as “Eljen” turquoise was claimed to be treated by a new proprietary process that improved the hardness and polish of soft porous turquoise. Testing showed it to be impregnated with a polymer, but it did seem harder than most impregnated turquoise, which would account for the improved polish (Owens andMagaña, 2009).
Natural opal—a hydrous, porous material—has a tendency to dry out and crack spontaneously. This tendency is so strong in opal from some deposits that most of the material is not usable in jewelry (e.g., Virgin Valley, Nevada). To address this problem, two new treatments were reported in the 2000s: (1) oil or wax impregnation of Mexican fire opal (Gambhir, 2001); and (2) a drying-out process followed by impregnation with a silica compound, used on Ethiopian opals (Filin and Puzynin, 2009).
As mentioned at the beginning of this section, impregnation was used on a number of the more unusual materials during the decade. These include quartzite (Kitawaki, 2002; Juchem et al.,2006), seraphinite (Henn, 2008), and sillimanite(Singbamroong, 2005). It even extended to some manufactured materials, most notably a much-debated material from Mexico called “Rainbow Calsilica” (Kiefert et al., 2002). This material required impregnation with polymers to be useful in jewelry, as it was very porous and would not take apolish in its original state (Kiefert et al., 2002; Frazierand Frazier, 2004).
Gemstone Luster Enhancement
This term is sometimes used to describe a treatment common to jade and some other gem materials in which a substance such as wax is rubbed on the surface of the stone to improve its appearance. The wax is only present on the surface and in depressions such as grooves in carvings, so it is not considered an impregnation. Although such substances are sometimes applied to pearls (Petersen, 2000), luster enhancement of pearls typically has a somewhat different meaning.
In the cultured pearl industry, the name Maeshoriis is associated with this kind of treatment (Akamatsu, 2007; Shor, 2007). Developed in the 2000s to improve the pre polishing process, it involves the use of solvents to “clean” nacreous pearls and hence produce a more lustrous surface. Various other forms of this treatment also exist (Lingyun et al., 2007). Polishing continues to be used on all types of nacreous and non-nacreous pearls to improve their salability. It takes place at all steps of the supply chain (Pousse, 2001), starting with the farmers, who often tumble their cultured pearls with walnut chips (N. Paspaley, pers. comm., 2008) and/or other materials and then polish them.
The first decade of the 2000s brought many new, unanticipated enhancements. Some of these—such as HPHT treatment and beryllium diffusion of corundum—usually cannot be identified by gemologists with standard equipment. In most cases, stones that might be treated by these methods must be sent to a well-equipped gemological laboratory to receive a conclusive identification. Still, today’s gemologist can benefit by developing their ability to recognize when a stone shows evidence it has not been treated (particularly for rubies and sapphires) and also recognizing when they cannot tell and the stone must be sent for further testing.
It is interesting that in their retrospective of the1990s article, McClure and Smith (2000) predicted that new filling processes would bring clarity enhancement to ruby, sapphire, and alexandrite. Three years later, at least part of this prediction came true with the development of a lead-glass filler for ruby. There is every reason to believe that this treatment, or a similar one, will soon extend to other relatively high RI materials.
Already in 2010 we have seen several new developments, including lead-glass filling of star rubies (Pardieu et al., 2010a) and a combination treatment of rubies from Mozambique that includes partial healing of fractures and partial filling with a glass that does not contain lead (Pardieu et al., 2010b).
With these developments, disclosure has become a significant topic at every trade show and gemological conference. As the trade discovered with emerald fillers (and the impact of nondisclosure on emerald sales) in the ‘90s, they neglect this subject at their peril. Consensus is critical. Discovering a treatment exists and developing identification criteria are important to the start, but the trade and gemological community must work together to address the issues of what to call a treated material, how to disclose it, and how to make sure it gets disclosed. Important steps in this direction have been made, but more are needed.
McClure and Smith (2000) also predicted—correctly—that technology would advance at an even faster rate during the next decade. This will undoubtedly be the case from now on, making the unforeseen the norm in the gemological world as it is in the world at large.
Jewelry Television® is as committed to education as it is to service and value. The purpose of this article has been to inform gem buyers of both traditional and modern gem enhancements that have either proven their reliability over time or show great promise for the future. Methods about which Jewelry Television® has reservations are not discussed here. For a thorough comprehensive listing and description of present-day enhancements, as well as the gems for which they are used, we invite you to view the JTV Gemstone Enhancement Chart.