Storm Over Sapphire

The controversy over the treated pink/orange “padparadscha-like” sapphire coming from Thailand is becoming more complex as research gemologists in the major laboratories study the stone’s chemistry, trying to figure out what’s creating the color. In fact, the investigation is expanding to most color varieties, including Mong Hsu and Songea ruby and blue-green, yellow, orange, and purple sapphires.

The decades-old surface-diffusion treatment of blue sapphire was 100% detectable—we knew how the color was introduced. But the new high-temperature sapphire enhancement performed in Thailand remains a mystery: We don’t know how it enhances color.

It’s synthetic. In an online newsletter, Ken Scarratt, director of the American Gem Trade Association’s Gem Testing Center, claims the high-temperature-treated sapphire has been altered to the point of recrystallization—using flux melts the surface of the heated sapphire, and when it cools, it recrystallizes, producing a synthetic surface.

“This is nothing new,” says Dr. Henry Hänni, director of the Swiss Gemmological Laboratory (SSEF) in Basel. But Hänni says the synthetic surface layer is “polished off.” He’s more concerned about the use of high temperature and flux for fracture healing. Hänni has shown that during heat treatment, fractures are indeed healed by synthetic corundum.

But Scarratt shows that synthetic features remain on the surface of some repolished sapphires that have undergone the new enhancement. And it’s not always identifiable. “The aggregate-like deposition of synthetic corundum at the surface of these newly treated stones typically can be evidenced by the multiple grain boundaries seen just below the polished surface of the stones,” explains Chris Smith, director of the Gübelin Laboratory in Lucerne. “However, sometimes with this new treatment, as well as with the more conventional heat treatment, the surface deposition of synthetic corundum can be more homogeneous or epitaxial [having the same growth orientation], and therefore it becomes much more difficult to identify.”

Moreover, the color of some treated material is not just confined to the surface layer but is diffused throughout the gem, making it virtually impossible to identify the type of treatment. “You can tell that the stones have been heated,” notes Smith, “but in relation to their origin of color, when the coloration is uniform throughout the stone, it is very difficult to distinguish it from more traditionally heat-treated fancy-color sapphires and rubies of the same hue.”

What controversy? According to a March 15 report from Thaigem.com (an online supplier of colored gemstones based in Thailand), the only controversy about this heat-treated sapphire is whether it “threatened the existing Padparadscha sapphire market.” Thaigem.com reported that Thai gemstone treaters feel that the brouhaha over their new treatment is a consequence of “an overly hasty tendency, on the part of certain gem labs at the start of the controversy, to question the legitimacy of the heating processes to which the sapphires had been subjected.”

Says Scarratt: “We stated clearly that from the evidence that we had before us—the color distribution and the apparent trace element concentrations … greater amounts of beryllium at the edge than in the center—the process used in the specific cases referred to was one of surface diffusion.”

Gemstone alert. Prior to February’s Tucson shows, AGTA’s Gem Testing Center sent out an “Urgent Gemstone Alert” that classified the padparadscha-like material as surface-diffusion treated. That message, later modified to exclude the term “surface-diffusion” (see “Four Labs Agree on ‘Padparadscha’ Terminology,” JCK, May 2002, p. 34), probably was the single most important factor in saving the U.S. gemstone market from becoming the dumping ground for a gem that now sells for pennies on the dollar.

The Thais cried foul, insisting that the new enhancement uses only high temperature and that no other elements were introduced. Then GIA found that beryllium had been added to the mix. But this effort was too late for some prominent Japanese gem labs that had already identified hundreds—possibly thousands—of carats of the material as solely heat-treated.

“The Thais are quite upset with the ‘surface diffusion’ identification, but that’s because the sapphires are still in Thailand,” notes Stuart Robertson, gem research director for The Guide. “And it remains the Thais’ problem. It’s all unsalable material at this point. The Japanese market has already been devastated.”

Robertson predicts that the entire sapphire market, ruby included, will take the kind of hit that emeralds—all emeralds, not just Colombian material—took after the Fred Ward emerald case. “Treatments must be accurately disclosed,” says Robertson. “It’s not just a matter of if, it’s a matter of when this one will show up in the consumer news. People just don’t accept these types of treatments, and especially not the way this was introduced.”

On Feb. 28, the Thai Gem and Jewelry Traders Association (TGJTA) asked representatives from various labs and those performing the new treatment to meet and discuss several aspects of the treatment as well as its disclosure. The gathering included representatives of TGJTA, the Chanthaburi Gems and Jewelry Association, AGTA, the Gemological Institute of America (GIA), Gübelin Gem Lab (GGL), the Gemological Association of Japan, Central Gem Laboratory (Japan), Swisslab (Bangkok), and—for the first time—representatives of the gemstone heaters of Chanthaburi, Thailand.

The beryllium factor. It’s unknown at this time if the new heat treatment adds anything to the stone to create more color. Beryllium has been found in higher-than-natural amounts in the new heat-treated stones, but, according to recent GIA research, beryllium itself does not produce color. “Investigation strongly suggests that beryllium is not the direct cause of the surface-related orange color layers,” says AGTA’s Scarratt. “However, it is possible that the diffusion of beryllium and perhaps other elements into the stone may be creating a reaction with the inherent chemistry in the corundum that gives rise to the yellow-to-orange coloration.”

Crystal manufacturer Swarovski, which is also marketing natural colored gems, has concluded research that may shed some light on the beryllium factor: When natural light-yellow chrysoberyl was, at first, inadvertently heat-treated along with light-yellow sapphire rough, beryllium from the chrysoberyl transferred to the sapphire. But some sapphire doesn’t change color, even when the beryllium is diffused into it.

Even if beryllium were the agent, positive identification of light elements like this is difficult and expensive. “No commercial lab today has the analytical capabilities to identify this,” says Smith. “Theoretically, SIMS and laser ablation might be able to detect this process.” He notes, however, that such services are not readily available to gem labs.

So the exact mechanism responsible for color change remains a mystery. Also unknown is whether any of the other induced elements play a role in color creation or if certain chemical requirements are necessary in the host material. “However,” writes Scarratt, “these imponderables are largely academic, as: 1) color has been artificially created; 2) foreign elements have been added (diffused into); and 3) redeposition (synthesis) has taken place.”

AGTA’s GTC and GIA’s GTL will now identify these gems as “natural corundum, evidence of heating and of surface-related color created by bulk diffusion.” When synthetic overgrowth is noted, the lab report will include “areas of synthetic overgrowth are present.” For the moment, Hänni doesn’t see a need to change policy. “There hasn’t really been any new revelation as to the mechanism for this color change,” says Hänni. “Why should we change our policy? We say that it’s treated.” What about the gems with color change throughout, with no diffusion elements observed? “This happens when you heat silk in Sri Lankan stones,” says Hänni. “It’s a diffusion process. Color is redistributed.”

The laboratory directors agree that much more discussion and research is needed before heat treatment’s effect on gemstones is fully understood. This situation is nothing new. Smith notes that there are already many enhanced gems that do not reveal any identifying enhancement characteristics. The list includes chemical bleaching to “whiten” the color of pearls; irradiation to create amethyst from colorless quartz, create or intensify the pink color of kunzite, and create or intensify the pink to red color of rubellite; and thermal enhancement to lighten the color of some dark blue sapphire, create citrine from amethyst, modify the color of “Paraíba” tourmalines, and remove the green color component of aquamarine.

These enhancements are undetectable. Many more, such as HPHT-enhanced diamonds, are not 100% identifiable. And as enhancement technologies come closer and closer to recreating the ways in which Mother Nature has created gems, the labs may not be able to identify enhancements 100% of the time. “Today, in most cases we are in position to identify a blue or fancy color sapphire and ruby as heated,” says Smith. “But what exactly the heat treatment has accomplished, we may not always be able to determine.”