Gemstone Enhancement: Clarity Enhancement, Irradiation and Combined Treatments, Surface Coating

by Shane F. McClure, Robert E. Kane, and Nicholas Sturman
from GEMS & GEMOLOGY, Vol. 46, No. 3, pp. 218240.
© 2010 Gemological Institute of America, Fall 2010
Published on  January 2012

This is Part II of a four part series on gemstone enhancement. See Part I and Part III.

See the end of this downloadable PDF for About the Authors, Acknowledgments, and a complete list of References.

Advances in technology and increased demand for lower-priced gemstone materials contributed to 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 article summarizes these developments and the methods used to identify the various enhancements.

Clarity Enhancement

During the 1990s, clarity enhancement was one of thejewelry trades most formidable challenges. Its usewith emeraldsin what had basically amounted to atrade secretwas touted publicly and almost causedthe crash of the emerald market. In addition, the clarityenhancement of diamonds spread rapidly, withimproper disclosure causing the ruin of some businesses.Clarity enhancement has remained a seriousissue in the 2000s. However, the methods changedand the focus has been on different gem materials.


The biggest concern about the clarityenhancement of diamonds via fracture fillingrevolved around the durability of the glass filler.Damage due to heat (figure 14) from standard jewelryrepair procedures, such as retipping, inevitablycaused problems at the retail level. One of the majortreaters (Oved) announced in 2000 that they haddeveloped a filler that could withstand such heat(Bates, 2000;Oved announces. . . , 2000). However,testing showed that although the new Oved fillermaterial seemed to withstand higher temperatures, itstill could be damaged by some jewelry repair procedures,even when performed by a master jeweler(Shigley et al., 2000). Oved instituted a policy of laserinscribing their company name on a bezel facet of allthe diamonds they treated so the filled stones couldnot be misrepresented (Gallagher, 2000).

The practice of laser drilling diamonds to createan opening through which acid could be introducedto remove a dark inclusion had remained unchangedfor many years, until a new version was introducedthat took advantage of advances in laser technology.Developed in Israel and referred to as the KM treatment(short for kiduah meyuhad, or special drillin Hebrew; Horikawa, 2001), this method did notactually drill a hole into the stones. Instead, it usedlasers to create a small fracture from the inclusion tothe surface so that the inclusion could be bleachedwithout leaving a tell-tale hole at the surface (figure15; McClure et al., 2000a). Unfortunately, this treatmententered the market undisclosed, and its fraudulentnature caused the Israel Diamond Bourse tooutlaw its use. It continues to be encountered, and isoften referred to as internal laser drilling.

Clarity enhanced diamonds

Identification is done with magnification. Thelaser leaves behind lines or dots of irregular squiggles,with feathers leading from an inclusion to thesurface (figure 16). These marks tend to look black intransmitted light, and are usually confined to afeather (McClure et al., 2000a; Cracco and Kaban,2002; McClure, 2003a). They may be tiny and difficultto find even with a microscopeor large andnumerous, easily seen with a loupe.

Other observations were posted in the literatureperiodically. Among them were changes in flasheffectcolors (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 associatedwith a pink dye (Yeung and Gelb, 2004).


The first report of faceted rubies showing aflash effect similar to that seen in clarity-enhanceddiamonds was in 2004 (Lead-glass impregnatedruby. . . , 2004). Chemical analysis revealed thatthese rubies were filled with a high-lead-contentglass. Soon other labs reported this treatment (Newtreatment on unheated rubies. . . , 2004; Rockwelland Breeding, 2004; Milisenda et al., 2005).

It became apparent that this treatment was goingto 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-temperatureheating, cleaning in an acid bath, and thenfilling with a high-lead-content glass, this non-gemcorundum was transformed into transparent, facetablematerial (figure 17). This made available hugeamounts of treated rubies that were usually sold atvery 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, althoughthe red color of the ruby sometimes partially maskedthe orange flash (McClure et al., 2006; figure 18).Flattened gas bubbles and high-relief unfilled areaswithin the fractures were also readily visible with magnification. However, the use of reflected light tolook for differences in surface luster was not veryhelpful in this case. The luster of this glass was verysimilar to that of ruby, sometimes even higher(Smith et al., 2005), so it was much more difficult tosee than the more typical silica glass fillers.

internal laser drilling on diamonds

The filler proved relatively durable to heat (up to~600ºC), but it was easily etched by even mild acidssuch as pickling solution (McClure et al, 2006). Thisetching turned the filler white near the surface, renderingit quite visible.

Also of concern was the decreasing quality of thestarting material. We began to see stones where theflash was everywhere, and internal filled cavitiescontaining large spherical gas bubbles were common(Scarratt, 2009).

The nomenclature for this treatment soonbecame an issue. The early material was referred toas clarity enhanced because even though the treatmentwas fairly extensive, the rubies were mostlysolid material that would be expected to stay togethereven without the treatment. However, some ofthe later material contained so much glass that itappeared the glass was actually holding the pieces ofruby together. Soaking such stones in hydrofluoricacid to remove the glass resulted in their fallingapart along fractures or being reduced to tiny pieces(Scarratt, 2009). Accordingly, GIA developed a threetieredsystem, keeping clarity enhanced for moresolid material, specifying ruby with glass for stonesthat needed the glass to stay together, and usingruby/glass composite for those composed of unrelatedpieces of ruby floating in glass (Scarratt, 2009; figure19). The other labs of the LMHC adopted thesecriteria. American Gemological Laboratories (AGL)and the International Colored Gemstone Associ -ation (ICA) have chosen to call all these stones compositeruby.

filling ruby with a lead-based glass

The real problem, however, is the large amountof 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), andestate jewelry (Quinn Darenius, 2010).


The damage caused to the emerald marketin the 1990s from lack of disclosure of clarityenhancement slowly began to fade in the 2000s(Gomelsky, 2003). However, the debate over the useof oil versus polymers as filler material continues,and a significant study was done on the durability offillers (Johnson, 2007).

To address the possibility that a highly fracturedstone was masquerading as a much finer one simplybecause of the treatment, labs started to state thedegree of enhancement on their reports (e.g.,McClure et al., 2000b). Different systems were developedwith anywhere from three to nine categories(Gomelsky, 2001a,b); the most common were threeorfour-tiered. Today, degree-of-enhancement callshave become standard procedure for emerald reportsfrom all the major laboratories.

best indications of lead glass fillings

Near the end of the decade, it was reported thatsome emerald rough was being stabilized withhardened polymers, so larger stones could be cut(Roskin, 2007; Federman, 2008). In effect, though,the polymer glues the pieces of emerald together atthe fractures (e.g., figure 20), so its removal wouldresult in the stone falling apart (Federman, 2007b).This situation is very similar to that of the leadglassfilled rubies, making disclosure even moreimportant.

Other Materials.

Laboratories have reported onmany other filled gems. Some of those mentioned inthe 2000s include: aquamarine and tourmaline(Wang and Yang, 2008; Deng et al., 2009), andalusite(Fernandes and Choudhary, 2009), fuchsite quartzite(Juchem et al., 2006), hackmanite (Wehr et al., 2009),and iolite (McClure, 2001).


Intense colors can be induced in many gems byexposing them to various forms of radiation, such aselectrons, gamma rays, or neutrons. To removeunwanted color overtones, some irradiated stonesare subsequently heated. While the 1980s saw significantexperimentation and development in the areaof gemstone irradiation, very few new types of irradiatedgems appeared on the market during the 1990sand 2000s. Likewise, little progress was made indetection methods.

For many gems, there is no definitive test orseries of tests to establish whether they have beenirradiated. Even though irradiation has been used formany years to produce intense colors in yellowberyl, pink-to-red tourmaline, and kunzite, theseenhancements remain undetectable. The same istrue for blue topaz and many other routinely irradiatedgem materials.

Blue irradiated (and annealed) topaz generates more than $1 billion annually in retail sales(Robertson, 2007). The low cost of irradiated bluetopaz (typically a few dollars per carat at wholesale)leaves the trade little economic incentive to determinewhether or not the gem has been treated. As aresult, all blue topaz is assumed to have been irradiated.The same is true for smoky quartz and darkyellow beryl.


With the staggering prices realized at auctionfor some fancy-color diamonds during the lastdecade (e.g., more than $1 million per carat for somenatural-color blue and green diamonds), there ishuge incentive to determine whether a diamondscolor is natural or irradiated. Large quantities of diamondscontinued to be irradiated (often followed bylow-temperature annealing at atmospheric pressures)to produce a wide variety of colorsred,orange, yellow, green, blue, violet, and purpleinsaturations from light to very dark (see Overton andShigley, 2008; Shigley, 2008). Many treaters producedsmall faceted irradiated (and annealed) coloreddiamonds for use in jewelry.

some lead glass filled rubies

The most significant developments in diamondirradiation since 2000 were in combination treatments.Both natural and synthetic diamonds arenow color enhanced by a process that involves firstHPHT annealing, then irradiation, followed by lowtemperatureheating (likely in that order), to produceseveral 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 alaboratory of the absorption and/or photoluminescencespectral features present with the diamondcooled to a low temperature, although in some casesstandard gemological testing can also offer clues (seee.g., Shigley, 2008). Other combinations also exist,such as irradiated and glass-filled diamonds (Gelb,2005; Gelb and Hall, 2005).


The potential enforcement of NuclearRegulatory Commission (NRC) guidelines on irradiatedgems (American Gem Trade Association, 2007)caused great concern in the first decade of the 2000s.Since 1986, NRC regulations have stated that anyneutron-irradiated gemstone produced in or importedinto the U.S. must be tested for residual radiationby an NRC-licensed testing facility (NuclearRegulatory Commission, 1986; Ashbaugh, 1988).Whereas considerable amounts of blue topaz wereonce treated in the U.S.and then properly testedfor radioactivity and held until the radioactivity subsidednearly all treated blue topaz entering themarket since the latter half of the decade has beenirradiated and annealed in other countries, some ofwhich may not restrict the export of hot material.

Amid the confusion generated by this issue, severalmajor retail chains and department storesstopped selling blue topaz. After receiving numeroustrade and public inquiries regarding blue topaz, theNRC issued a fact sheet on irradiated gemstones(United States Nuclear Regulatory Commission,2008). To further address the issue, the JewelersVigilance Committee (JVC) and American GemTrade Association (AGTA) published a 2008brochure titled The Essential Guide to the U.S.Trade in Irradiated Gemstones.

emerald with resin binding material

To our knowledge, the NRC has still notenforced its regulations, and neutron-irradiated bluetopaz continues to be imported and sold in the U.S.However, no blue topaz containing residual radioactivityhas been reported recently in the trade.

Earlieraround 2000Europe faced similar concernsthat irradiated blue topaz exhibiting residualradioactivity had made its way into several differentcountries (Kennedy et al., 2000).

U.S. Postal Service Irradiation.

During the anthraxscare of late 2001, the USPS irradiated envelopes andpackages to kill potential biological agents. Thecompany that the postal service contracted with toperform the test, SureBeam, used a linear acceleratorto create a beam of high-energy electrons. Thepotential impact of this exposure was immediatelyrecognized, since the same ionizing radiation is routinelyused to change the color in several types of gems. McClure et al. (2001) showed alarming evidenceof several gems that had their color changeddramatically after being exposed in SureBeams facilityto the same dosage as was used for the mail. TheUSPS subsequently abandoned these procedures,after determining that the time and money neededto sanitize all mail would be prohibitive.

Green Quartz.

In the latter part of the decade, anunusual amount of faceted green quartz suddenlyappeared on the world market. Nearly all thesegemswhich originated from Rio Grande do Sul,Brazilbegan as colorless to light yellow quartz thatwas subsequently irradiated to produce the greencolor (Kitawaki, 2006; Schultz-Güttler et al., 2008).Natural green quartz does exist but is extremelyrare, and greened quartz (also known as prasiolite)is produced by heating certain types of amethyst.Irradiated green quartz shows a broad spectralabsorption at 592620 nm, while prasiolite exhibitsa broad band centered at 720 nm. When examinedunder a Chelsea filter with incandescent light, irradiatedgreen quartz appears red and prasiolite appearsgreen (Schultz-Güttler et al., 2008; Henn andSchultz-Güttler, 2009).


In addition to the huge quantities of irradiatedyellow beryl, which remains undetectable, irradiatedyellowish green beryls were seen. Milisenda (2007a)reported absorption lines between 500 and 750 nmfor the ordinary ray, which are also typically seen inartificially irradiated Maxixe-type beryls. Mili -senda (2007b) reported a beryl with Maxixe-typespectra that was offered for sale as a cats-eye scapolitebut proved to be a blue irradiated cats-eye beryl.


Milisenda (2005a) reported on a parcel ofintense green faceted spodumenes from Pakistan,offered for sale in Idar-Oberstein as hiddenite, thatwere artificially irradiated. The stones revealed abroad absorption band centered at 635 nm. Asexpected for this material, the color faded to the originalpale pink within a few days.


The irradiation of pearls has been known fordecades, and little has changed since 2000. The treatmentis almost always associated with freshwaterpearls or nuclei, since the radiation appears to alterthe state of the trace element manganese found inthese materials. Gray, silvery gray, and black colorshave all been produced. In fact, pearls were one of thegems significantly altered by the U.S. postal serviceirradiation mentioned above. Detection remains achallenge in some cases, and research has continuedon its identification (Liping and Zhonghui, 2002).


As it has been for centuries, applying surface coatingsto change the color of gems continues to be acommon practice. Not only do gemologists need tobe aware of high-tech coatings, we must alsoremember to look for older, simpler alterations.Diamonds. Just as Miles (1964) described decadesago, in 2003 Sheby reported seeing two slightly yellowdiamonds that were coated with a blue materialto improve the apparent color. Also as a recentreminder, Eaton-Magaña (2010) described a 1.5 ctdiamond with a color equivalent to Fancy pink thatrevealed a nearly imperceptible trace of reddishmaterial on a natural when viewed with the microscope.After cleaning, the diamond was graded Faintpink.

Sputter-coated optical thin films were originallydeveloped in the 1940s to improve the optical performanceof lenses. We continued to see similar coatingtechnology used on diamonds in the 2000s. Evans etal. (2005) and Wang et al. (2006b) reported on faceteddiamonds that were colored pink by sputter-coatedthin films. A potentially new kind of diamond coatingwas described by Epelboym et al. (2006)ratherthan using the fluoride coatings previously known,pink and orange-treated diamonds were suspected ofbeing coated with a silica film doped with gold.

Shen et al. (2007) reported that the trade was submittinggreater numbers of pink diamonds coated bycalcium fluoride (CaF2) to the GIA Laboratory forgrading and origin reports. They also describedSerenity Technologies use of multiple micro-thincoatings of various compositions to produce a varietyof colors on diamonds, including intense blue,green, yellow, and orange to pink to purple-pink (figure21).

We continue to see crude yet effective coloredcoatings applied to the girdle facets of diamondswith permanent markers and solutions made fromcolored art pencils.

Diamond-Like Carbon Thin Films.

Super-hard coatings,such as diamond-like carbon (DLC) films, arebecoming increasingly popular for a variety ofmechanical, scientific, and technological applications,such as cutting tools, razor blades, and thelike. This technology is also making its way into thegem industry. Several companies, including SerenityTechnologies and Zirconmania, market DLC-coatedcubic zirconia. Eaton-Magaña and Chadwick (2009)reported that these products were easily separatedfrom diamond.

coatings on diamonds

Serenity Technologies also offers a patent pendingnanocrystalline diamond coating processnamed Diamond Rx which they apply to a varietyof gems, including emerald, apatite, chrome diopside,zircon, peridot, tourmaline, kunzite, tanzaniteand aquamarine (Serenity Technologies, 2010). Theymaintain that such coatings are extremely durable.However, it is very difficult (and sometimes impossible)to identify whether these DLC coatings are infact even present on a gemstone.


In April 2008, a Los Angeles gem dealerencountered two parcels comprising a few hundredcolor-coated tanzanites (E. Caplan, pers. comm.,2010; figure 22). Research concluded that the smallerstones (4.5 mm) could be identified on the basis ofunusually intense color for their size, by areas ofwear seen with microscopic examination, and byunusual surface iridescence (American Gemo -logical Laboratories identifies. . . , 2008; McClureand Shen, 2008). Larger stones (e.g., 3+ ct) weremuch 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 tanzaniteshave all but disappeared from the market.


In the late 1990s, we began to see different colorsof topaz (blue-to-green, orange, pink, and red) thatwere being represented as diffused (Fenelle, 1999;McClure and Smith, 2000). Schmetzer (2006, 2008)reviewed the patent literature and concluded that thevarious mechanisms and treatment methods were notdiffusion and should all be described as surface coated.However, Gabasch et al. (2008) showed that certaincolors were due to coatings, whereas others werediffusion-induced. For more details, see the section ontopaz under Diffusion Treatment above.


Typically, gem coatings are ultra-thin.However, Hänni (2004) described black coral (alsoknown as horn coral) that was coated with severalrelatively thick layers of artificial resin.


Any gem can be coated to alter its color, providea degree of protection, improve the luster, ormask some imperfection. Pearls usually fall into thelatter three categories. Porous by nature, pearls maybe coated for protection from harmful chemicals. Orthey may have luster and/or surface imperfectionsthat a coating can hide. In this decade, a number ofcoatings were applied to natural and cultured pearls(Moses and Reinitz, 2000; Hurwit, 2002; Krzemnicki, 2005a; Shor, 2007). One development in particularthat should be carefully monitored by thepearl industry in the future is the application of DLCcoatings (Drucker, 2008) to improve durability.

tanzanite coated with cobalt-colored material

Related Articles