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
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 theproliferation of new treatments throughout the first decade of the 2000s. The developments thatmade the most difference were the diffusion treatment of corundum with beryllium, diffusion ofcopper 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 upwith these treatments, and the jewelry trade has struggled with how to disclose them. This articlesummarizes these developments and the methods used to identify the various enhancements.
Another decade has passed since we reviewedthe events of the 1990s as they pertained togemstone enhancements and their detection(McClure and Smith, 2000). At that time, weobserved that the issue of disclosure (and, especially,the failure to disclose) had caused major upheaval inall areas of the jewelry industry. We ended that retrospectivearticle by stating there would be no end tofresh challenges in treatment identification and disclosureas we entered the new millennium.
The 2000s certainly lived up to our expectations.There were treatments discovered that no one suspectedwere possible. There were crises of disclosurethat resulted in televised exposés and unfavorablepublicity for the industry. There were improvementsin treatments developed in the ’90s that made themmore efficient and often harder to detect.
Detection methods have also become more andmore complex. Gemological laboratories have had toinvest in more sophisticated instrumentation, sometimesat great expense. For the frontline laboratories,being a good gemologist is no longer good enough.You must also have training in the earth sciencesand analytical instrumentation to function effectivelyin such an environment. Now more than ever, thegemologist in the trade must be able to recognizewhen a stone requires more advanced testing.
It is important to emphasize that many of thesetreatments can still be detected with standard gemologicalequipment, but staying current on the latestdevelopments is absolutely essential. The knowledgebase concerning treatments is constantlychanging.
Nearly every gem material (e.g., figure 1) is subjectto treatments of one form or another. Building onprevious reviews (Kammerling et al., 1990a; McClureand Smith, 2000; Smith and McClure, 2002), the aimof this article is to provide an overview of the treatmentsand identification challenges associated withthem that were common during the first decade ofthe 2000s. The authors strongly recommend thatreaders familiarize themselves with the original references,as all the pertinent information cannot be presentedin a review article.
Although there is no global standard regardingspecifically how a seller should disclose gem treatmentsor enhancements, there is general agreementthat they should be disclosed. This disclosureshould be to all purchasers, at all levels of commerce(from miner to cutter, wholesaler, jewelrymanufacturer, retailer, and—ultimately—the consumer).To find the proper protocol in your countryor area, contact one of your national or regional coloredstone and diamond organizations, such asAGTA (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 beknown as the Laboratory Manual HarmonisationCommittee (LMHC) was formed at the request ofleaders of the colored stone industry. Its purpose wasto bring together representatives of many of themajor gem laboratories and attempt to standardizewording on their reports (“International labs. . . ,”2000). The LMHC is autonomous and has representativesfrom the U.S., Switzerland, Thailand, Italy,and Japan. If agreement is reached on a given subject,they issue an information sheet with the wordingexpected 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 (todownload these standardized nomenclature sheets,go to www.lmhc-gemology.org/index.html).
For a wide variety of gem materials, heat treatmentis still the most common enhancement. In somecases, heat treatment can still be identified by routinemethods. In others, conclusive identification ispossible only with advanced instrumentation andtechniques. In still other gems (e.g., aquamarine, citrine,amethyst, and tourmaline), heat treatmentremains virtually unidentifiable by any currentlyknown methods. For this last group of stones, whichare heated to induce permanent changes to theircolor, this enhancement may be the rule rather thanthe exception. One should assume that most ofthose gem materials have been heated.
High-pressure, high-temperature (HPHT) treatmentof diamonds was only introduced commerciallyin 1999, and much of the first decade of the 2000swas devoted to expanding this high-tech treatmentto colored diamonds on the one hand—and detectingit on the other. Research efforts thus far have providedmethods to identify not only the lightening of offcolordiamonds, but also the production of a widevariety of fancy colors.
The last decade bore witness to thegreater presence of color-treated diamonds, with theglobal trade reportedly approaching 25,000 carats permonth in the latter half of the decade (3–5% of thetotal diamond trade; Krawitz, 2007). Although notspecifically noted, this figure probably refers mostlyto irradiated and annealed diamonds of many differentcolors. Irradiation, heating, HPHT, or a combinationof these treatments can create virtually everyhue (figure 2), including black and colorless.
HPHT Treatment to Remove Color. HPHT treatmentof diamonds to remove or induce color was acentral topic of the diamond community throughoutthe 2000s. In 1999, General Electric Co. and LazareKaplan International announced the commercialapplication of an HPHT process for faceted diamonds(Pegasus Overseas Limited, 1999) that removed colorfrom brown type IIa stones (by annealing out vacancyclusters associated with the brown color in plasticallydeformed diamonds; Fisher, 2009). Even thoughscientists had recognized these and other possibilities30 years earlier (see, e.g., Overton and Shigley, 2008),the results came as a surprise to many in the diamondworld—a type IIa brown diamond of any sizecould be transformed into a colorless stone (see, e.g.,Smith et al., 2000). After HPHT treatment, themajority of these diamonds received D through Gcolor grades, and the results were permanent (Moseset al., 1999). Gemological researchers globally mobilizedto 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 IIaHPHT-treated diamonds had been seen at the GIALaboratory (McClure and Smith, 2000). Today, withseveral treaters in various countries removing colorfrom diamonds with HPHT annealing, this treatmenthas become almost commonplace.
Determining diamond type is central to thedetection of colorless to near-colorless HPHT-treated diamonds. For a thorough review of how diamondtype 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-treateddiamonds reported in the literature have beentype IIa. Fortunately, it is easy to determine if a diamondis not a type IIa by using the DiamondSure(Wel bourn et al., 1996), SSEF Type II DiamondSpotter (Boehm, 2002; Hänni, 2002), or other simplegemological methods (Breeding and Shigley, 2009).At the present time, if a colorless to near-colorlessdiamond is not type IIa, then it is not HPHT treated.
Visual features related to damage caused by theextreme conditions of the treatment may be seen insome colorless to near-colorless HPHT-treated diamonds.These include a frosted appearance caused byetching or pitting, as well as gray or black graphitization,on naturals or fractures where they come to thesurface. Such features are not commonly observed inuntreated colorless type IIa diamonds, although lightlypitted surfaces and graphitized or graphite inclusionshave been seen on rare occasions. Therefore,such features are a good indication of treatment, butthey are not proof by themselves (Moses et al., 1999;McClure and Smith, 2000; Gelb and Hall, 2002).Because these heat damage−related features are notalways present in a faceted diamond or may be difficultto discern, detection of HPHT treatment in atype IIa diamond generally requires measurement ofthe absorption and/or photoluminescence (PL) spectrataken 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 andSpits, 2000; Hänni et al., 2000; Smith et al., 2000;Collins, 2001, 2003; Novikov et al., 2003; andNewton, 2006).
HPHT Treatment to Produce Color. Refinementsto HPHT processing have yielded commercial productionof a variety of colors in both type I (orangyyellow, yellow, to yellow green) and type II (pink orblue) diamonds (Shigley, 2008; see, e.g., figure 3).
Identifying HPHT-treated type Ia diamondsrequires both IR and low-temperature visible-rangespectroscopy, but several gemological propertiesoffer evidence (see Reinitz et al., 2000). The pink andblue HPHT-treated diamonds initially examined byHall and Moses (2000, 2001b) ranged from Faint andVery Light to Fancy Intense and Fancy Deep. LowtemperaturePL spectra identified these products. Asdiscussed below, combining treatments (e.g., HPHTannealing, irradiation, then low-temperature heating)can produce interesting results, such as intensepink-to-red diamonds (Wang et al., 2005b). Smith etal. (2008a,b) contributed useful charts for identifyingthe natural or treated origin of color in pink and bluediamonds.
Heat-Treated Black Diamond. In the late 1990s, itbecame 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 isoften the case with successful jewelry lines, lessexpensiveapproaches soon followed. Harris andVance (1972) had experimented with the productionof artificial graphitization in diamond, which Halland Moses (2001a) confirmed by heating a sampleunder vacuum for a few minutes to several hoursand turning it black; Raman spectra showed a patternthat matched graphite. Notari (2002) discussedseveral different commercially practiced methods ofheating to produce graphitization and black colorationin diamonds.
In many cases, microscopic examination withfiber-optic illumination can provide proof of heattreatment in black diamonds—the black (graphitized)areas are largely confined to surface-reachingcleavages and fractures (Hall and Moses, 2001a). Innatural-color black diamonds, the graphitization israndomly dispersed throughout, referred to as a “saltand pepper” effect (Kammerling et al., 1990b). Thisrandom orientation is also seen in other color-causinginclusions in natural-color black diamonds, suchas magnetite, hematite, and native iron (Titkov etal., 2003). This determination, however, requires agemologist experienced in examining known samplesof both natural-color and heat-treated black diamonds(see, e.g., Smith et al., 2008c).
As in the preceding two decades,the heat treatment of corundum to substantiallychange its color remained a troublesome issue.Heating was applied to the vast majority of rubiesand all colors of sapphires during the 2000s.
In some cases, clarity was also affected, as withthe flux-assisted healing of fractures (in combinationwith high-temperature heat treatment) that began inthe early 1990s with the discovery of huge quantitiesof ruby at Mong Hsu, Myanmar (see Peretti et al.,1995; figure 4). The 2000s ushered in a greater understandingof this material—which dominated the rubymarket—and cooperation between gemological laboratoriesto adopt standardized wording to describeheat treatment in corundum and, most importantly,the degree to which fracture “healing” has occurredand the amount of solidified flux “residue” (see e.g.,www.lmhc-gemology.org/index.html). Today, thereis less production of ruby at Mong Hsu, but this techniqueis now being used on rubies from Africa (Shorand Weldon, 2009).
There were also new areas of concern, such asberyllium diffusion with high heat (see “DiffusionTreatment” below) and the “Punsiri” high-temperaturetreatment for blue sapphires. With regard to thelatter, concerns arose in late 2003 when some laboratoriesfirst observed unusual color concentrations inlarger heat-treated blue sapphires (figure 5) immersedin methylene iodide (Scarratt, 2004; Smith et al.,2004). All had one consistent characteristic: a colorlessor near-colorless outer rim and a deep blue (or, ifcolor change, purple) interior (figure 6).
After comprehensive analytical research (and GIAand AGTA observation of the technique as performedby treater Tennakoon Punsiri in Sri Lanka), the SSEF,AGTA, and GIA laboratories all came to the sameconclusion: These stones were not diffused withberyllium or any other element (McClure, 2003b;Hänni et al., 2004; “ICA issues its first lab report. . . ,”2004). The major gem labs continue to identify sapphirestreated by the “Punsiri” method as natural sapphiresthat show evidence of heat treatment.
Beginning mid-decade, demand and scarcity significantlydrove up prices for colorless or “white”sapphire. As a result, dealers in Sri Lanka reportedthat lightly colored sapphires had been heated to renderthem colorless (Robertson, 2008). Ironically, thescarcity of natural white sapphire was caused in partby 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 articleson treatments (Kammerling et al., 1990a; McClure and Smith, 2000), heat-treatment technology—in the form of electric furnaces with precisetemperature and atmospheric controls—has becomemore sophisticated and accessible. During the 1980sand 1990s, nearly all commercial corundum heattreatment was being conducted in Thailand. WhileThailand remains important, Sri Lanka is now amajor force, and smaller yet very effective corundum-heating capabilities exist in other producingregions such as Africa, Myanmar, China, and theU.S. (Montana). Nevertheless, some pink sapphiresand rubies continue to be heated using simple blowpipemethods 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 andproperties of sapphires and rubies. During the pastdecade, a number of articles addressed heat-treatmenttechniques and their effects on gem corundum fromlocalities 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 identificationof natural, heated, and Be-diffused yellow toreddish orange sapphires from Sri Lanka, Montana,Madagascar, and Tanzania. David and Fritsch (2001)contributed a valuable study on the use of infraredspectra to distinguish heated rubies and sapphiresfrom 20 different geographic origins.
Proof that a ruby or sapphire has been heat treatedis sometimes readily apparent, but in many casesit requires considerable knowledge and observationalskills. The criteria for identifying heat treatment inrubies and sapphires using a microscope were setforth during the 1980s and ’90s (for a summary, seeKammerling et al., 1990a). Most still apply. Theyinclude stress fractures surrounding melted or heatalteredinclusions; spotty coloration in blue stones,best seen with diffused illumination; colored halossurrounding 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 bluecolor component, is still very difficult to detect withstandard microscopic testing. The lower the temperatureused, the more difficult the detection will be(Krzemnicki, 2010).
Equally important is being able to prove that aruby or sapphire has not been heat treated. Thedecade yielded rich contributions in this area; seeShor and Weldon (2009) and Shigley et al. (2010) forimportant literature references. Smith et al. (2008d)and Smith (2010) provided useful charts for identifyingthe natural or treated state in rubies and sapphiresfrom around the world.
Amber and copal are still heated to improveclarity, color, and hardness, and to induce “sun spangles”(Kammerling et al., 1990a; O’Donoghue, 2006).In 2009, Abduriyim et al. described a new method toproduce a green color in amber and copal (figure 7),some as bright and green as peridot, using a twostageprocess of controlled heat and pressure in anautoclave for long durations. Multiple treatmentsmay increase the color saturation, producing anintense, pure green hue that has not been seen inuntreated amber. The treatment also reportedlyhardens the amber, making it more stable (Abduri -yim et al., 2009). While infrared spectroscopy candistinguish amber from copal (Guiliano et al., 2007),this new treatment process “ages” the copal, renderingits properties similar to those of amber and makingits identification as copal extremely difficult,even with advanced analytical methods.
The presence of a small absorption around 820cm−1 in the FTIR spectra confirmed the use of multipletreatments on all the commercial “green amber”samples tested by Abduriyim et al. (2009). Althoughthe use of heat treatment on a specific piece can beascertained, whether or not the original startingmaterial was copal or amber still cannot be routinelyidentified.
Around 2003, members of the trade beganreporting that Russian demantoid is routinely subjectedto low-temperature heat treatment to remove orreduce the brown color component (“The reds. . . ,”2003; N. Kuznetsov, pers. comm., 2003). Other thanthe presence of altered inclusions in some stones, nomeasurable gemological means of detection has yetbeen reported. The result is that some internationallaboratories make no determination of whether ademantoid has been heated, whereas others willstate if indications of heating are present (Pala Inter -national, 2010).
As was the case with garnet, it was longbelieved that spinel was never treated. Beginning in2005, however, researchers determined that certainpink-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 offine gems from melee sizes up to 10–50 ct (Pardieuet al., 2008). Again, rumors of heated spinel began tocirculate. This prompted researchers to conductbefore-and-after heat treatment studies of spinelfrom various localities. It was concluded that heatedand unheated natural spinel could easily be distinguishedby the width of the 405 cm−1 Raman line, orby examining the width of the Cr3+ PL spectrum linein stones containing sufficient chromium (Saeseawet al., 2009b,c; Kondo et al., 2010).
The heat treatment of Cu-bearing tourmalinesfrom Paraíba, Brazil, and the enormousdemand for both the natural-color and heat-treatedmaterial, continued through the decade. An interestingtwist occurred when Cu-bearing tourmalineswere discovered in Nigeria (Smith et al., 2001;Breeding et al., 2007) and Mozambique (Abduriyimand Kitawaki, 2005; Abduriyim et al., 2006; Laurs etal., 2008).
These tourmalines were commonly heated (e.g.,figure 8) to create a wide range of attractive colorssimilar to many of those found in Paraíba. With theexception of obviously heat-altered inclusions, standardtesting cannot identify heat treatment in thesetourmalines.
For several decades, heat has been known toreduce saturation in overdark red tourmalines.However, many cutters resist heating these stonesbecause tiny fluid inclusions tend to burst duringheating and cause breakage (B. Barker, pers. comm.,2008).
Faceted orangy, pinkish, and yellowishbrown zircons from Tanzania, known by tradenames such as “cinnamon” zircon, were plentiful inthe market (see figure 1, no. 10). To lighten overdarktones, nearly all such stones in the market havebeen heated—often in a test tube with low heat (R.Shah, pers. comm., 2010). Since there is no means ofidentifying whether these gems—like blue zircon—have been heated, we recommend that all zircon ofthis color range be considered as heated.
Although not widely recognized,heat is sometimes used to alter the appearance ofcultured pearls. Heat alone usually produces moresaturated yellow colors, and other effects can resultwhen heat is used in combination with other methods(“Better techniques improve brown pearls,”2006) such as bleaching. In all cases, detecting heattreatment can be challenging. There are no obviousthermally enhanced inclusions as in some gems, andthe only useful methods determined to date usuallyinvolve UV fluorescence reactions and UV-Vis-NIRspectroscopy (Elen, 2001; Wade, 2002).
Diffusion treatment was more problematic for coloredstones than any other enhancement in the2000s. Beryllium diffusion, in particular, “upped thebar” on the sophistication of equipment and level ofknowledge needed by gem laboratories.
Titanium diffusion of sapphire continuedthroughout the decade, with one instancereported of these stones sold in Australia as heattreatedCeylon sapphire (“Fusion treated sapphirealert,” 2001). Little changed with this method, andits identification remains the same—color concentrationalong facet junctions, facet-related color, highrelief in immersion, and the like (Kane et al., 1990).Chromium diffusion of corundum has beendebated as being more of a chemical reaction at thesurface of the stone than true diffusion. It was actuallyshown on some stones to be a synthetic rubyovergrowth (Smith, 2002). This treatment is very difficultto perform, and to the authors’ knowledge isnot currently being used.
The diffusion of corundum using cobalt was alsoreported in the last decade (Kennedy, 2001; McClure,2002b), but this material was easily identified withmagnification and diffused light by a very shallowcolor layer that showed spotty coloration, as well asobservation of a cobalt spectrum with a desk-modelspectroscope.
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 heattreatment done in Thailand. Some labs in Japan aresaid to have issued over 25,000 reports stating just that(Genis, 2003; Weldon, 2003). In early 2002, however,examination with the stones immersed in methyleneiodide revealed that they had a surface conformal layerof orange color surrounding a pink core (Weldon, 2002;figure 9). With this discovery, the illusion that thecolor was caused by “standard” heat treatment beganto crumble (“Orange crush,” 2002).
The story is well documented by Emmett et al.(2003). At first, the reason for the orange surfacerelatedcolor zone could not be determined. Thestandard equipment available in gemological laboratoriesdetected 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 colourin treated pink sapphires,” 2002; Hughes, 2002;Genis, 2003). Unfortunately, beryllium was almostunknown in corundum, with very little informationavailable in the literature.
There were two major differences between Ti andBe diffusion. First, beryllium, being a very smallatom, was capable of diffusing all the way througheven large sapphires. Titanium could not do this,even with heating times lasting several weeks.Second, titanium is only capable of creating bluecolor in sapphire. Beryllium, however, can affect virtuallyevery color of corundum in some way whencombined 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 padparadschacolor; dark brownish red to bright red; anddark inky blue to lighter blue—just to name some ofthe possibilities (Coldham, 2002; Henricus, 2002;Moses et al., 2002).
Identifying this treatment turned out to be complicated.Severely heat-damaged inclusions werefound in many of these treated stones (Roskin,2003a; Schmetzer and Schwarz, 2005), but they onlyindicate 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 seeBe-diffused blue sapphires treated by an even newermethod that showed no surface-related characteristicsand created unusual inclusions (figure 12;Choudhary, 2006; Kitawaki and Abduriyim, 2006;Roskin, 2006; DuToit et al., 2009). These inclusionsalso did not prove Be treatment, but they stronglyindicated that further testing was needed.
Areas of synthetic corundum overgrowth werecommonly seen on Be-diffused faceted stones, but Bewas not necessary for this to happen (McClure,2002a). UV fluorescence was helpful in some situations,but not all (Fritsch et al., 2003). Even chemicalanalysis was a problem, as the standard instrumentsused at gemological laboratories and most universities(EDXRF and electron microprobe) cannot detectlight elements such as beryllium. Detecting Bemeant using instrumentation such as mass spectrometers.At that time, no gemological laboratory possessed this capability, so testing had to be done atcommercial laboratories, which is very expensive.Today, several gem labs have this equipment inhouseand offer Be testing as a service.
In 2002, a transparent red feldspar coloredby copper debuted on the market, reportedly originatingfrom the Congo. This did not raise suspicioninitially, as natural red feldspar colored by copperwas already well known (from Oregon). Over time,however, the supposed location of this feldspar minekept changing—to “China,” “Inner Mongolia,” andthen “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 hadnothing to do with treatment, but focused onnomenclature (Krzemnicki, 2004a): Was itlabradorite or could it be called andesine? Andesinewas rare in gem quality, so this could be very valuableto marketing efforts. Although much of thematerial was indeed andesine, in time this became asecondary issue. Large amounts of this feldspar werebeing sold as all-natural, untreated material. In July2008, however, Masashi Furuya of the JapanGermany Gemmo logical Laboratory reported that hehad direct evidence (from experiments done inThailand) that this feldspar was being diffusion treatedby a three-step process that took months to complete(Furuya, 2008). He also mentioned the sametype of material being diffused in China by anunknown process.
Other reports suggested that the unusual colorzoning found in this material indicated diffusiontreatment (Fritsch et al., 2008). Subsequent studiesconflicted with this idea, showing natural Oregonmaterial with very similar zoning (McClure, 2009).
To address the controversy, systematic experimentswere undertaken to diffusion treat plagioclase.They showed it was surprisingly easy to duplicatethe Cu-diffusion process in only a few days(Roskin, 2008; Emmett and Douthit, 2009). Also,gemologists visited a mine in China’s InnerMongolia that produced andesine-labradorite, but only with a pale yellow color (Abduriyim, 2008). Thematerial could not be simply heated to red or greenbecause it contained virtually no copper (Thiran -goon, 2009). This fact left diffusion as the only possibletreatment method for these stones.
Claims of a mine in Tibet began in 2005, buttheir credibility was questionable. In 2008, a teamvisited a mine in Tibet, collected samples, witnessedmining, and documented red andesine that appearedto be in situ (Abduriyim, 2008). However, the samplescollected proved to be virtually identical to thediffused Inner Mongolian red andesine, calling themine into question again. Its authenticity is still notresolved.
With the controversy surrounding this material,identification of this feldspar as treated is still problematicusing standard gemological techniques, primarilybecause the issue of the Tibet mine is notresolved. Color zoning may be useful. A complete“bull’s-eye” color zoning with red-inside-green usuallymeans the stone is natural, while green-insideredmay indicate treatment (McClure, 2009).However, if you have a partial “bull’s-eye” or merelyzoned areas, this criterion is unreliable. To date, largerplatelets of copper have been found only in thenatural Oregon material (McClure, 2009; Rossman,2009, 2010). However, separation of Oregon andChinese feldspar in a gemological laboratory is notdifficult as they are all distinct chemically.
Blue-to-green topaz surface-treated withcobalt was marketed in the 2000s as an alternativeto irradiated blue topaz (Federman, 2007a), a tacticthat took advantage of the public’s fear of radiation.This material has long been marked as “diffusiontreated,” even though this claim was never trulysubstantiated. Gabasch et al. (2008) determined that the layer of coloration was “diffusion induced,” creatingnew phases at the surface. This is not so differentfrom the opinions put forth in the late ’90s thatthe treatment was more of a chemical reaction thandiffusion.
Several companies announced lines of “diffusiontreated topaz” in new colors of red and pink to“champagne” and bicolors (Roskin, 2003b; “Diffusedtopaz from India,” 2003), but questions still exist as towhether they are from a diffusion or coating process.Identification of this material is fairly easy. Withmagnification, 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 colorlessnature of the base topaz.
The discovery that diffusion treatmentof feldspar was possible generated claims thatmany other gems—such as Cu-bearing tourmalinefrom Mozambique, Imperial topaz, and tsavorite(Federman, 2009)—were also being diffusion treated.To date, no significant scientific data have been presentedto support these claims, though experimentshave begun to explore some of these possibilities(Saeseaw et al., 2009a).
There was one report of tanzanite possibly beingdiffused, but examination of the suspect stonesshowed no evidence of diffusion (Wang, 2003).
Published January 2012
Published January 2012
Modified May 2011
Modified April 2011
Modified April 2011
Modified April 2011
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