Gem dealers in Thailand discovered years ago that heating ruby often improves its color. Early methods were crude, involving furnaces made of 55-gallon drums lined in clay. The heat not only deepened the color but also sometimes would dissolve silk inclusions and thereby enhance the clarity of the gem.

We learned to accept heat treatment without reservation mostly because we had no other choice. Unheated gems commanded a premium price, but the market for these rare finds was limited. Then in 1991, everything started to change.

Mong Hsu ruby debuts. That year a new deposit of ruby was discovered in the Mong Hsu region of Myanmar (Burma), southeast of the historic Mogok deposit. By 1992 the new Mong Hsu ruby began to appear in Bangkok, the ruby-trading capital of the world. Abundant and affordable, the new Burma rubies initially generated excitement. But the enthusiasm soon cooled.

The reason had to do with fracture filling. When mined, the Mong Hsu rubies were bicolored, with a blue sapphire core encased in ruby. When heated, the blue core turned to red and the silk-like inclusions dissolved. But other inclusions, typically surface- reaching fractures, didn’t respond to traditional levels of heat. The fractures rendered the gems unsaleable.

Up to the mid-1980s, Bangkok treaters had typically heated rubies to 1,600 to 1,800°C, aiming specifically to improve the color and reduce the visible silk inclusions. They later modified this enhancement to fill cavities as well. The modified process involved packing the gems in borax and then heating the crystals. The borax acted as an insulator and would melt, forming a glass that filled any surface cavities.

The latest heat treatment goes beyond this, almost to the melting point of corundum—2,050°C. This requires insulation in borax, silica, or aluminum. As the crystal heats up, the fractures transform into a molten state and “heal” themselves. The extreme heat and the borax/silica/alumnium flux promote the healing of fractures. As the ruby cools, the treatment can leave a glass-like residue on the surface, in fractures, or even sometimes encased in healed fractures within the gem.

After treatment, the gems are washed in an acid bath to remove any residue left from the borax, silica, or aluminum. Often, however, the acid bath does not remove all the residue from the surface or within the gem.

Concerns over residue. In 1993 European and Japanese buyers in Bangkok balked at accepting filled rubies. Two years later the Japanese filed a formal complaint with the Thai Gem and Jewelry Traders Association (TGJTA). No longer would they buy rubies with residue. Later, this led to proposals whereby buyers agreed to accept filled rubies only if the residue were invisible at magnification levels of 10x or lower. TGJTA members—knowing that their pocketbooks could be greatly affected—responded by claiming that they would use only borax as insulation. Supposedly, borax is easier to clean up with an acid bath. Gemological sources suggest that this may still leave some residue, especially within the ruby.

Some in the trade say they would never accept a ruby that contains any residue. But the superheat has been so successful that Thai treaters now use it almost exclusively. An estimated 95% of all rubies sold in Thailand are from the Mong Hsu deposit. One Thai lab estimates that filling is present in 90% of the Mong Hsu material, whether in cavities, fractures, or healed fractures.

Responding to the negative reaction of major buyers, the Thais developed a coding system for their rubies. Category A is “natural ruby”—enhanced by heat with no residue visible at 10x on or within the stone. Category B is “heat-enhanced natural ruby”—with some residue visible at 10x within the stone. Category C is “heat-treated natural ruby with foreign substances present”—with some residue visible on the surface and within the stone at 10x. They also have a category for “unheated natural ruby.” Does this simplify matters or make them more complex?

“Unintentional” byproducts. Some treaters maintain that the glass-like in-filling is an unintentional byproduct of an otherwise normal enhancement process. If we consider heat a necessary step to bring rubies to the marketplace, then we must accept a minute amount of foreign substance. Although the amount of filler is minimal, some traders note that it enables stones just shy of full-carat weights to hit the round number.

But just how “unintentional” is this byproduct? At first, I, like others in the trade, used this term to defend the process. I’ve since altered my view. When an emerald is oiled, fractures become less visible. That’s the intent of the process. When a ruby is heated, the color improves. That too is the intent of the process. When superheat heals fractures in ruby, that is clearly part of the intent. Treaters are aware of the glass-like in-filling. That’s why the fractures are healed. The rubies in the end look better. Every part of the process is intentional. Even if the process were discovered serendipitously, the results are now known. Thus the process must be considered intentional.

Some take a hard-line approach and say the Bangkok treaters are out to deceive. This attitude stems from the fact that throughout history new treatments and synthetics have appeared from all over the world, and jewelers seem to be the last to know about them. Perhaps the treaters thought we couldn’t notice and it would simply be business as usual. More than likely, they never expected the results they achieved. They then assumed the trade would accept the rubies unconditionally. After all, the rubies did look better, so wasn’t the treatment really a bonus to the industry? As concerns about enhancements have set in, however, the prices for all rubies have begun to slide. On the heels of the emerald problems, the trade must be prepared for a rocky road ahead for rubies.

Identification difficulties. The first step in proper disclosure is to identify the glass-like residue. Surface residue is relatively easy to ascertain. Using overhead reflected light, the swirly liquid-like surface residue typically can be noticed at 10x magnification. In some cases higher magnification may be necessary.

Internal residue poses more of an identification problem because its fluid appearance can resemble flux, the material that’s caught in healed fractures. Flux is generally associated with the synthetic gemstone process. For that reason, some in-filled and healed rubies have been misidentified as synthetic.

I experienced this difficulty first-hand when a ruby was sent to me for appraisal. My initial observation revealed the flux-like area shown in the photo on page 190. The flux appeared wispy and in high relief, as you’d expect with a synthetic. I almost misidentified the ruby until I found the inclusion seen below. The crystal inclusion is angular and surrounded by intersecting planes, proving that the ruby is not synthetic.

Tucson tap-dance. Strolling among the dealers in Tucson this past February, I anticipated new answers to the disclosure question. What I found instead was a widespread lack of disclosure, whether through intent or ignorance. While some were quick to respond to questions about treatment, they usually denied any glass filling. They admitted to heat but said their rubies definitely contained no foreign substance. Can we believe them? If the Thais are right in saying that 90% of ruby is superheated, we need to be cautious and check even the ones that reportedly are not filled.

Others at the Tucson shows were hesitant or uncertain when asked about heat treatment. Was it because they knew the rubies were filled and were attempting to hide the facts? Was it because they simply didn’t know and were afraid to say so? Maybe they suspected it but couldn’t say for sure. All are possibilities.

One thing is certain. Sales for ruby were down this year. As a jeweler, would you want to invest thousands of dollars on a gemstone when the dealer says, “I’m not sure”? On the other hand, what if a dealer says, “Yes, there is some foreign material in this gem”? Would you still buy it?

A call for full disclosure. The real problem with disclosure is that education takes time. Much remains to be learned about heat treatment of ruby. The more secretive the treaters are, the greater the chance the ruby market will suffer. Hopefully, the industry will learn from previous mistakes in the emerald market. Intentional nondisclosure of a treatment process could seriously hurt the ruby market, as it did with emeralds. Prices for emeralds are about half what they were a few years ago.

Where do we go from here? Honesty and integrity will go a long way to maintain market confidence. That means full disclosure of heat treatment. Yes, this is heated. Yes, there is a residue within the ruby. And yes, that’s why the price I can sell this for is lower than it would be otherwise.

This is yet another choice for consumers. Just as synthetics provide a lower-priced alternative for consumers, so too do in-filled rubies. No one would suggest selling a synthetic ruby as natural (although unfortunately it does still happen). By the same token, it’s simply not prudent to sell an in-filled ruby as completely natural.

Richard B. Drucker is president of Gemworld International and publisher of The Guide, a pricing periodical he began in 1982.