In the spring of 1979, the Gemological Institute of America’s Gem Trade Labs (GTL) began to see a large number of heat-treated sapphires from Sri Lanka. Robert Crowningshield, then director of GTL in New York, called heat-treating sapphires “one of the best kept commercial secrets in the jewelry industry.” That’s because the Sri Lankans (and later the Thais) had been treating stones for almost six decades, but neither GIA nor the rest of the industry learned of it until the 1970s.
In “The History and Politics of Heat,” published last year in Gem Market News by Gemworld Inter-national, Northbrook, Ill., gemologist and corundum expert Richard Hughes of Pala International, Fallbrook, Calif., revealed that GIA had seen the heated stones but didn’t realize it. Hughes and others have found the particulars in GIA’s own Gems & Gemology magazine.
“In 1966, Robert Crowningshield of the GIA described a blue sapphire, reportedly from Thailand, that displayed a very weak spectrum and a greenish-white short-wave UV fluorescence,” says Hughes. “Later, he reported on a fine natural blue sapphire of 18 carats that displayed a zoned greenish-white fluorescence under short-wave UV. Today, we know such reactions are common in heat-treated sapphires, particularly those from Sri Lanka.”
Ignorance is bliss. In the early 1900s, the high-temperature furnaces creating Verneuil synthetic rubies and sapphires had been well established. Curious natural-gem dealers, heat-treating with much lower temperatures, worked side by side with those making synthetics to see what would happen if natural gems were heated to higher temperatures. Like all trial-and-error experiments, there were failures and some successes.
No one acknowledged the “successes” as different from natural unenhanced gems. Hughes says those first heated corundums allegedly originated from the Pailin mines in Cambodia. Treated Cambodian rough was reportedly given to lapidaries to cut as far back as 1915, which means many might still be worn by people who believe they have a natural-color sapphire.
It wasn’t until some 60 years after these initial trials that heat treatment of sapphire and ruby gained worldwide attention with the discovery of the heat-treated geuda sapphire.
Hand in hand. The situation was this: On the one hand, Sri Lankans and Thais could make beautiful gems out of vast quantities of geuda sapphire, which without heat was unsalable material. This relieved the market, which was suffering a major shortage of fine-quality sapphires and rubies.
On the other hand, a heated gem should be worth less than a naturalcolor gem, but because disclosure was nonexistent, and there wasn’t enough unheated material in the market to compete, that’s not what happened.
So by 1977, almost all corundum was being heated. As Hughes says, “Large numbers of heat-treated Sri Lankan sapphires were streaming out of Thai ovens.”
In August 1978 JCK wrote about the “Corundum Crisis,” a shortage of ruby and sapphire that had prices skyrocketing and Thai dealers coming to New York to buy goods. U.S. dealers were complaining about scarce goods and escalating prices.
“We’re seeing far fewer better colors of sapphires, because the supply of stones suitable for burning has fizzled out,” said one dealer. In the summer of 1978, for example, prices rose at least 30% from June to September.
With prices for fine-quality corundum on the rise, and no distinction being made between heated and natural, the trade was in chaos, says Joseph Menzie, expert sapphire wholesaler in New York. “There’s always been heat treatment,” he says. “They discovered a way to heat geuda, which increased the number of stones in the market.” But when the trade found out about heat treatment, and what they were using to create such fine gems, Menzie says, “The trade made a lot of noise.”
But it was too late. Heated stones had a six-year head start on the wholesale trade, which meant that the natural-color sapphire and ruby trade had already been using heated stones to alleviate their shortage. The notion that heat treatment of low-quality gems to improve color and clarity was necessary to furnish fine-quality gems to the consumer was reality.
Consumers were untroubled. In a 1983 JCK consumer poll, 72% of respondents said they would choose a heated sapphire over a natural sapphire if the price were lower.
The starting material, labeled geuda, was poor-quality faceted and cabochoned translucent near colorless to milky yellowish-white stones, included with rutile needles. Geuda sapphires, considered industrial quality, were ignored by the trade. It was being bought for a song by Thai treaters and sent back to Bangkok for heating to enhance clarity and color. The gems were then repolished and sold for enormous profit.
As Dave Federman, gemstone editor for JCK in the late 1970s, remembers, “There were lines of dealers waiting to have their stones heated by these guys. The gem industry in Bangkok replaced Colombo as the sapphire capital of the world.”
Once the Sri Lankans understood what was being done, they slapped a blockade on exports and began learning the modern art of heat treatment.
Trade and consumer acceptance. Some say the trade had to accept heat treatment of corundum since it was already in the market. Others say there wouldn’t be a market without the high number of stones now available because of heat treatment. But what do consumers think?
A recent JCK Retail Panel found that consumers “were occasionally surprised” when told about heat treatment of gems, but that didn’t stop them from buying. “At first they’re hesitant,” said panel members, “but when you give history, show beauty, explain it is permanent, then it’s okay.” A number of panel members noted that only one out of every 20-50 customers request an untreated stone. As for those who do not, jewelers concluded, “They must have no problem with it.”
Below the melting point. By the early 1980s, the phrase “heat treatment” was common nomenclature, and the word “flux” also entered gemologists’ vocabulary. The word on the street was that borax flux was used in the heat treatment process.
Over the past few decades of geuda heating, many gemologists have stated that, when heat-treating sapphires and rubies, the gems are coated with or immersed in a borax flux to “help protect them against thermal shock.” Not so, says Dr. John Emmett of Crystal Chemistry, Brush Prairie, Wash., a leading expert in heat treatment of corundum. In a 1999 Gemological Symposium presentation he wrote, “Natural ruby and sapphire are highly resistant to thermal shock fracture. … Fluxes are used solely to enhance the appearance of lesser-quality material.”
Others have noted that flux was used to lower the melting point of corundum to allow for better enhancement. This is, in part, correct: Emmett says flux can have many functions, including dissolving the surface, filling and masking surface-reaching fractures and cavities, and—upon cooling—redepositing dissolved corundum, resulting in regrowth (also known as “synthetic overgrowth.”)
The same was true for Mong Hsu Burma ruby. In the mid-1990s, a deposit of ruby was uncovered showing good color but with a blue/black core. Its clarity is considered translucent to opaque; what some have called “red-blue fish-tank gravel.” Using temperatures as low as just above 900ºC, the material could be greatly clarified and color enhanced.
TE1 through TE6. After extensive research, the Gübelin Gem Lab in Lucerne, Switzerland not only developed a grading system for the healed appearance but also noted one important fact from Emmett’s presentation—one overlooked by most gemologists: “Naturally occurring inclusions (such as phyllo-silicates) also may melt under high temperatures and assist in healing fractures, without the additional use of chemicals, and leave an amorphous residue behind.”
According to Emmett’s report, this residue and healing is left after partial melting and recrystallization of fracture walls. The residue is trapped solidified material in either glass or crystallized form. Since trapped flux looks like trapped melted mineral inclusions, identification of chemically induced and non-chemically induced healing is not yet possible.
The Gübelin lab’s ranking system focuses on the remnants of these trapped solids rather than on the identification of the remnants. It also doesn’t consider the amount of fracture healing since it’s impossible to tell the extent of a former fissure.
Instead, the lab ranks the gemstone enhancement TE1 through 6 (TE means thermal enhancement) from best to worst. “As less healing has taken place, proportionally more residue may be present in negative crystals, communication tubes, and thin films.” (“NTE” is used for rubies or sapphires where “no indication of thermal enhancement” is present.)
The question of whether to call the healed fissure a “synthetic growth” is still one for discussion.
Diffusion equals deception? By the mid-1980s, another new word had surfaced—”diffusion.” It was used to describe the introduction of coloring agents, in particular titanium, into the top surface layer of colorless faceted sapphire to create beautiful blue sapphire. The word “diffusion” made sense to gemologists. Unfortunately, it didn’t follow well-established scientific terminology.
When it became known that heat was being used to infuse color-causing elements into sapphire, a line was drawn in the sand: This, not traditional heat, was considered deception. What made it easy to rebuke was that the color layer was thin and could, if the gem were repolished, be removed, leaving the original colorless stone. What made it all the more important was that the treatment could be easily identified using a microscope.
But diffusion isn’t the culprit. Diffusion is simply movement of elements to create color centers or destroy color centers. Heat with no additives such as flux or coloring agents causes elements already present in a gem to move about, creating or destroying color centers, dissolving minerals, and recrystallizing minerals. Every gemstone that’s heated has had some form of diffusion taking place within it. Therefore, all heated gems are, by definition, “diffusion treated.”
Enter Madagascar. In the 1990s, vast deposits of sapphire were discovered in Madagascar. Because the gems were similar to Sri Lankan material, heat was applied to test for enhancement capabilities. Unlike Sri Lankan sapphires however, the color of the gems could be dramatically altered at only 300ºC to 400ºC.
Thai and Sri Lankan stones are cooked at approximately 1,300ºC. At this temperature, rutile can be dissolved, leaving only remnants of the inclusion and a clear crystal gem. Madagascan stones with no rutile are heated only to improve color, so high temperature for dissolving inclusions is not a requirement.
Inclusions in Sri Lankan sapphires that explode from heat stress or melt from high temperature do little if anything under the low-temperature heating of Madagascan stones. Many treaters don’t even consider low temperatures to be “heat-treatment,” but the wholesale trade does. If wholesalers aren’t told about heat treatment, and if there are few if any physical indications of what has been done to stones, disclosure is all but impossible.
This can make life miserable for the gemologist—including the professional laboratory gemologist. It’s possible to send a Madagascan stone to all of the major New York gem labs for color origin determination and get a difference of opinion.
Tom Moses, vice president of identification services at GIA’s New York GTL, knows that the trade expects the labs to determine whether a gem is heated or not. “But it’s not always like that,” Moses says. “The labs can have the same list of 10 identification indications, and eight or nine of the indicators will be judged exactly the same at both labs, but the tenth suggests something different for each. Therefore, even though the identification processes may be within a tenth of each other, the results are miles apart.”
What next? So, we’re left with “traditional” heat-treated sapphires and rubies that are both readily identifiable (Sri Lankan) and not so identifiable (Madagascan), all of which are “diffusion treated” in the proper scientific sense of the word. Some have had their surface-reaching fractures healed using their own elements, while others have been healed using flux additive elements—making the stone “partially synthetic”—and the two are indistinguishable. Some have even had shallow color enhancement from using flux with coloring additives. Because of its nonpermanence, however, this type of treatment has been castigated.
Next month, we’ll address bulk lattice diffusion and high pressure, high temperature treatment, both difficult if not impossible to identify. Some in the industry believe that high temperature treatments could finally cook the heated gemstone industry’s goose.