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Article Index- Gemstone Enhancement and its Detection in the 2000s: Thermal Enhancement and Diffusion Treatment
Gemstone Enhancement and its Detection in the 2000s:
Thermal Enhancement and Diffusion Treatment
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 I of a four part series on gemstone enhancement. See Part II 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.
Another decade has passed since we reviewed the events of the 1990s as they pertained to gemstone enhancements and their detection (McClure and Smith, 2000). At that time, we observed that 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 disclosure as we entered the new millennium.
The 2000s certainly lived up to our expectations. 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 and more complex. Gemological laboratories have had to invest in more sophisticated instrumentation, sometimes at 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; McClure and 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. The authors strongly recommend that readers familiarize themselves with the original references, as all the pertinent information cannot be presented in a review article.
NOMENCLATURE AND DISCLOSURE
Although there is no global standard regarding specifically how a seller should disclose gem treatments or enhancements, there is 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 Federation of 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 expected to be seen on reports from those labs. To date, 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).
THERMAL ENHANCEMENT
For a wide variety of gem materials, heat treatment is still the most common enhancement. In some cases, heat treatment can still be identified by routine methods. In others, conclusive identification is possible only with advanced instrumentation and techniques. In still 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 of 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 offcolor diamonds, but also the production of a wide variety of fancy colors.
Diamond.
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 (3–5% 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 (figure 2), including black and colorless.
HPHT Treatment to Remove Color. 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 results came as a surprise to many in the diamond world—a type IIa brown diamond of any size could be transformed into a colorless stone (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 (Moses et al., 1999). Gemological researchers globally mobilized to understand and identify the process (e.g., Chalain et al., 1999, 2000; Schmetzer, 1999; Collins et 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 DiamondSure (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, on naturals or fractures where they come to the surface. 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. Refinements to HPHT processing have yielded commercial production of a variety of colors in both type I (orangy yellow, yellow, to 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. Lowtemperature 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 black diamonds 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, lessexpensive approaches soon followed. Harris and Vance (1972) had experimented with the production of artificial graphitization in diamond, which Hall and 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—the black (graphitized) areas are largely confined to surface-reaching cleavages and fractures (Hall and Moses, 2001a). In natural-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 et al., 2003). This determination, however, requires a gemologist experienced in examining known samples of both natural-color and heat-treated black diamonds (see, e.g., Smith et al., 2008c).
Ruby and Sapphire.
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 (Shor and Weldon, 2009).
There were also new areas of concern, such as beryllium diffusion with high heat (see “Diffusion Treatment” 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 GIA and 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 Ti blue 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, and smaller yet very 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 blowpipe methods at mine sites and trading centers in Vietnam, 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, see Kammerling et al., 1990a). Most still apply. They include stress fractures surrounding melted or heataltered 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., 800–1200°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).
Equally important is being able to prove that a ruby or sapphire has not been heat treated. The decade yielded rich contributions in this area; see Shor and Weldon (2009) and Shigley et al. (2010) for important literature references. Smith et al. (2008d) and Smith (2010) provided useful charts for identifying the natural or treated state in rubies and sapphires from around the world.
Amber.
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 twostage 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 820 cm−1 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.
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 Inter - national, 2010).
Spinel.
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 (6–54 kg) spinel crystals were faceted into many thousands of fine gems from melee sizes up to 10–50 ct (Pardieu et al., 2008). Again, rumors of heated spinel began to circulate. This prompted 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 cm−1 Raman line, or by examining the width of the Cr3+ PL spectrum line in stones containing sufficient chromium (Saeseaw et al., 2009b,c; Kondo et al., 2010).
Tourmaline.
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 (Abduriyim and 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.
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 overdark tones, nearly all such stones in the market have been heated—often 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 zircon of this color range be considered as heated.
Cultured Pearls.
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-NIR spectroscopy (Elen, 2001; Wade, 2002).
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.
Titanium diffusion of sapphire continued throughout the decade, with one instance reported of these stones sold in Australia as heattreated Ceylon sapphire (“Fusion treated sapphire alert,” 2001). Little changed with this method, and its identification remains the same—color concentration along facet junctions, facet-related color, high relief in immersion, and the like (Kane et al., 1990). 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 surfacerelated 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 colour 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— 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 inhouse and offer Be testing as a service.
Feldspar.
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 then “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. Color zoning may be useful. A complete “bull’s-eye” color zoning with red-inside-green usually means the stone is natural, while green-insidered may indicate treatment (McClure, 2009). However, if you have a partial “bull’s-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.
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.
Other Materials.
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 have been presented to support these claims, 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).
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