NOMENCLATURE AND DISCLOSURE
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, andultimatelythe 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 handand 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 (35% 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 diamondworlda 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.