When Customers Want Untreated Gems

Is the issue of gem treatments attracts more public attention, consumers’ interest in and demand for untreated gems is likely to grow. To make sure rising demand doesn’t outstrip supply, logic dictates that miners and cutters should stop—or at least curtail—treatments. Logic, however, won’t trump tradition, and the enhancement habit has been ingrained for generations. Besides, most untreated gems simply aren’t saleable.

The key to resolving this dilemma is understanding the effect of treatments on pricing and disclosing to your customers every bit of information about the treatment of the gem they want.

Price. Pricing is based on this assumption: A gem that can be treated has been treated. Corundum pricing, for example, takes for granted that gemstones have undergone heat treatment. Emerald pricing assumes that a slight amount of oil or resin has been added. If a gem that can be treated has not been treated, a premium applies to its price.

There are exceptions and complications. Tanzanite is an exception, because without heat treatment, there would be none—there’s no “natural” option. As for complications, even though prices are set in terms of premiums for untreated gems rather than “discounts” for treated gems, “excessive” treatment does bring a discount. Dealers vary widely in their assessments of premiums and discounts. Nevertheless, some useful guidelines have been developed, as I’ll explain.

Emerald. A variety of oils, plus Opticon and other resins, both natural and synthetic, are used to treat emeralds. Durability and stability vary, and the acceptability of each treatment is still debated. Because it’s so difficult to accurately identify a particular treatment, many labs determine the amount of treatment instead. Observing the internal characteristics of an emerald allows a reasonably accurate assessment of the level of treatment, which is correlated with premiums and discounts, as shown in the table below. (The rarity of untreated emeralds in today’s market makes it impossible to determine an exact premium for high-end goods.)


Commercial Good Fine Extra-Fine
Untreated +5% to +10% +10% to +25% +25% to +50% +50% to ?
Treatment Level Slight 0% 0% 0% 0%
Treatment Level Moderate 0% to -5% -5% to -10% -10% to -15% -15% to -25%
Treatment Level Extensive -10% to -15% -15% to -20% -20% to -25% -25% to -35%

Ruby. Since the standard treatment for ruby is heat, unheated rubies bring a premium. But make sure you understand how origin fits into the pricing equation. An unheated ruby from Thailand will command a premium, but an unheated ruby from Mogok, Burma, may be worth twice as much (or more) as the unheated Thai stone. The table below pertains to ruby from all locations except Burma.

The heating process leaves glass residue in some rubies. The amount of residue affects pricing, but because it’s more difficult to determine how much glass is in a ruby than it is to determine the amount of filler in an emerald, prices for rubies are even more subjective than those for emeralds. Stones with large cavities intentionally fused with glass to conceal the cavity are easy to spot and severely discounted.


Commercial Good Fine Extra-Fine
Unheated 0% to + 5% +5% to +20% +20% to +35% +35% to +50% or more
Heat Treatment 0% 0% 0% 0%
Slight Glass Residue 0% 0% to -5% -5% to -10% -10% to -15%
Moderate Glass Residue 0% to -5% -5% to -10% -10% to -15% -15% to -20%
Extensive Glass Residue -10% to -15% -15% to -20% -20% to -25% -25% to -35%
Cavity Filled -10% to -50% -10% to -50% -10% to -50% -10% to -50%

Sapphire. Heat also is the standard treatment for sapphire, so an unheated sapphire commands a premium. Again, don’t confuse the origin issue with the premiums expected. For example, unheated sapphires from Burma and Kashmir will command larger premiums than those from other sources. The glass residue problems associated with ruby don’t affect sapphire.


Commercial Good Fine Extra Fine
Unheated 0% to +5% +5% to +10% +10% to +20% +20% to +30% or more
Heat Treatment 0% 0% 0% 0%

Selling untreated vs. treated gems. I believe in full disclosure. That includes telling a customer that tanzanite is heat-treated even though the treatment has no effect on the price or the sale. Why do that? It fosters trust. Assume your customers will hear about treatments somewhere—on the street, from another jeweler, or on TV. If you give them the information first, they’ll respect you and feel comfortable relying on your knowledge.

Other treatments, of course, are more difficult to deal with.

Ruby. Telltale signs of heat treatment include burst inclusions with halos or partially dissolved silk. After you explain this to a customer, expect some questions. Respond positively, not defensively. Let customers know that most rubies are heated to improve their color (and sometimes their clarity) and explain that the ruby market is based on this reality.

Don’t reject the possibility of finding an unheated ruby. You don’t want your customer to think you’re hiding something or unwilling to work hard for her. Acknowledge that unheated rubies are available but point out that they’re very rare. Explain the premium associated with unheated stones and inform the customer that it could take some time to locate one. If she’s willing to pay the premium and wait, finding one may be worth your effort, since a higher profit is possible.

How can you be sure a ruby has not been heated? If the aforementioned telltale signs of heating aren’t present—or if, for example, an inclusion isn’t burst—the gem probably hasn’t been heated. But the customer will probably want a guarantee before paying extra for an untreated ruby, so it’s best to send the stone to a lab.

Emerald. Selling untreated emeralds is more difficult. Most are oiled right out of the mine, and an “au naturel” emerald is a rarity. In fact, emerald is the most difficult of the “big three” gemstones to obtain in a natural state.

The rarity of natural emeralds has put the focus on type of treatment. A customer may have heard about Opticon and oil and possibly even Gematrat. Whether one is better than another has yet to be determined by researchers, and “better” may not translate into “more acceptable.” Some dealers still insist on oil (the traditional treatment), even though other fillers may be more durable and stable. Some fillers may do a superior job hiding flaws, but whether that’s a positive trait or a negative one is still debated, adding to the complexity of the issue. But complexity doesn’t excuse you from the responsibility of answering questions.

If a customer demands an emerald treated by a specific process, you’ll need to provide a guarantee. Get it from your supplier, who can make the guarantee or send the stone to a qualified lab for the paperwork. (Obviously, this isn’t cost-effective for smaller or less expensive gems.) Suppliers today face lots of questions about treatments. Unfortunately, many will say whatever it takes to make the sale. Forewarned is forearmed: Get your guarantees in writing.

A more serious problem occurs if a customer insists on a natural emerald. Your suppliers are not likely to have any. In fact, there’s no source I know of for a consistent supply of untreated emeralds. Your best bet is to buy a slightly enhanced emerald and have the filler removed. Why “slightly enhanced”? Such a stone will undergo the least change in appearance once the filler is gone. After the emerald is cleaned out, submit it to a gem laboratory for authentication papers.

If you buy an emerald with a report stating “natural untreated,” here’s a caveat: Some unscrupulous dealers have been known to clean emeralds, submit them to a lab, then re-treat the stones with oil or resin.

The lab factor. Now that certificates are commonplace, you’ll need a paper “guarantee” to sell an important untreated gem. Certificates from the Gemological Institute of America’s Gem Trade Lab will state evidence of treatment or lack thereof. The American Gemological Laboratories, the American Gem Trade Laboratory in New York, and the Swiss Gemological Laboratory (SSEF) specialize in detecting treatments. Other labs, such as the European Gemological Laboratory, the International Gemmological Institute, and the Gem Quality Institute, also perform treatment analysis. Depending on the lab, analysis will identify the treatment, quantify it, or do both.

We recently learned that some fine cutters in Idar-Oberstein, Germany, had been using a wax treatment on cabochon-cut tourmalines without informing their customers. When Josh Hall of Pala International questioned the cutters, they replied, “We thought everyone wanted us to do this.” Hall has since asked them not to treat his tourmaline, but the incident serves as a cautionary tale: In a world where it’s possible for suppliers to sell treated goods without even knowing it, the labs are your best protection.

Beyond the “big three.” Some gems aren’t treated because traditional treatments don’t work on them. Garnet and peridot are examples. If consumers begin to demand untreated gemstones, their popularity may jump, a situation sure to affect pricing.

Spinel is another gemstone that so far has escaped treatment. Many gem dealers agree that it isn’t well understood by jewelers or consumers. Confusion between natural and synthetic spinel may have contributed to its underpricing today, but, like garnet, it could be a gem for the future.

Richard B. Drucker, G.G., is the president of Gemworld International and publisher of The Guide, a pricing periodical he began in 1982. An international gemstone consultant, he has published numerous books on the jewelry industry.