The proliferation of modern gem treatments began in earnest in the 1960s, when the worldwide demand for rubies, emeralds and sapphires grew to new levels, and the mines could no longer supply nearly enough high- quality gem specimens to meet the burgeoning market. Over the decades, the situation has worsened as a result of both natural and political factors.

"At this point, even the most sophisticated consumers are generally not aware that most stones are treated. As they become aware of treatments, they will start searching for natural or minimally treated stones, and that will drive up the prices in the years to come."

The scarcity of natural stones is largely the result of hundreds of years of mining in core regions such as Burma and Kashmir, where many gem deposits have been depleted. In more recent times, unstable governments and harsh climates have made development of major mining operations by outside investors nearly impossible.

But while natural untreated stones are increasingly difficult to obtain, they are not wholly unavailable. These natural gems command top dollar: a sizeable untreated ruby, for instance, has been known to fetch twice the price of a treated stone of a similar size.

Antoinette Matlins, a noted gemologist consultant who wrote Colored Gemstones, the Buying Guide, says consumers should expect to pay $100,000 a carat for a high-quality, certified natural ruby, pure red and transparent. "If a client requests a five-carat natural, beautiful color ruby," she says, "it could take several months to locate a stone of that caliber." More than likely, Matlins says, she would expect to find this type of natural gem through an estate collection; the most perfect rubies came out of Burma before the borders closed. By comparison, a moderately heat-treated ruby, considered standard practice today, might fetch only 25 percent of the value of a certified natural stone. Of course, with all colored gemstones, it is the imperfect ones that will be subject to the alchemist’s legerdemain.

Virtually all emeralds are oiled, and have been for hundreds of years to keep them from cracking, but the top-of-the-line emeralds need only a slight oiling with a colorless substance. Such a gem can be even more costly than a ruby; Matlins estimates a top-quality, lab-certified natural emerald of about five carats could easily cost $300,000.

"Stones have been oiled or heated for hundreds of years. It’s become almost impossible to find newly mined stones that have not been thermally treated."

A treated emerald with a tinted oil to enhance its color is most likely of lesser quality to begin with, and would be worth at least 50 percent to 75 percent less.

The price differential between a natural and a moderately enhanced sapphire is not as vast as rubies and emeralds. Matlins estimates a high-quality natural Ceylon sapphire, considered to be among the most desirable, costs between 30 percent and 50 percent more than a moderately heat-treated stone of similar size. Ceylon sapphires are a lighter shade than the crystal Burmese sapphire, which is usually a deep indigo, or the velvety-toned Kashmir variety. Ceylon sapphires tend to be a cornflower blue, though some verge on pastel. Heat treatments often reduce transparency and muddy the crystal effect, yet naturally darker sapphires are often treated to lighten the color, while those that seem too pale might be X-rayed to intensify the color.

Despite the high price tag of natural gems, Matlins believes they are still a good investment. "At this point, even the most sophisticated consumers are generally not aware that most stones are treated," she observes. "As they become aware of treatments, they will start searching for natural or minimally treated stones, and that will drive up the prices in the years to come."

Consumers might be surprised to find out that even the most prominent jewelry houses, including Tiffany & Co. and Harry Winston, will accept certain standard treatments that improve the color of a gem. However, they steer clear of any process that changes the color of a stone, masks inclusions or flaws, or increases the weight of a gem through the impregnation of a foreign substance. Tiffany’s, for instance, accepts heat treatments of rubies and sapphires to improve color and clarity, and the infusion of a colorless substance to improve clarity without increasing the weight of the stone.

"Anything done to mask any inclusion is not acceptable, because that deceives the eye," says Melvin Kirtley, group vice president at Tiffany’s. "We provide full disclosure of any treatments with every gemstone."

Tiffany’s is employing some of the world’s most advanced technology in its own gemology labs to detect treatments. There are certain standard treatments, such as the heating of corundum (sapphires and rubies) which is considered permanent, according to Kirtley. These are acceptable, but such treatments as resins impregnated in emeralds are not.

Harry Winston sells emeralds that have been oiled, a practice that can protect the stone from cracking, but Ronald Winston, the company’s chairman, is quick to point out that he will not accept colored oils that camouflage the original shade of the gemstone.

"Stones have been oiled or heated for hundreds of years," Winston says. "It’s become almost impossible to find newly mined stones that have not been thermally treated."

Considering the challenges in obtaining natural gems, Harry Winston often turns to estate collections to uncover untreated gems, and they are always accompanied with a laboratory report from a prominent lab such as Gübelin Gem Lab in Lucerne, a gemological consulting lab that serves both the industry and the public.

While thermal heating of sapphires and rubies and oiling of emeralds is an accepted industrywide practice, buyers should avoid stones with other treatments that may not be permanent, might affect the durability of a stone or conceal a significant flaw, advises Andrew Lucas, product manager of gemology at the Gemological Institute of America. Certain treatments, such as colored oil on emeralds, can fade over time or when a stone is cleaned.

Other common treatments include diffusion, a process that exposes the surface of rubies and sapphires to chemicals, and prolonged heating to enhance color. Fracture filling is another typical practice; it fills a stone’s fracture with oil, wax, glass or epoxy resin. While these treatments can be permanent, they will greatly reduce the value of a stone.

Leading gem laboratories have been able to detect most treatments. However, even the gem experts have trouble with some of the newest techniques. The American Gem Trade Association Gemological Testing Center has begun to encounter a new heat treatment that it cannot identify in a growing number of blue sapphires. While the lab has been evaluating and testing these sapphires for more than a year, it still does not have conclusive information about this treatment. Until it can identify the enhancement, it refuses to issue reports on the stones.

Aside from whether a gem is natural or color-enhanced, its country of origin also plays a role in determining its value. The world’s finest rubies come from the Mogok Valley of Upper Burma and are identified by a subtle florescence that exists only in gems mined in that region. The first known mined rubies from Mogok Valley date back to 1496, but Burma’s mines have been sealed off since a government crackdown in 1962, and even before that the Mogok mines were running out of reserves. The Muzo and Chivor mines of Colombia have produced the best emeralds for centuries, while Ceylon, Burma and Kashmir are the sources of the most coveted
sapphires.

Today, the landscape of gem mining has been greatly altered. While many of the great historical mines are not producing stones, other sources have opened up in Afghanistan, Pakistan and Russia. The mines of Madagascar and Tanzania—where a new deposit recently turned up—are emerging with their own versions of blue sapphire.

Some experts say, however, that the quality of the gems from these sources does not begin to approach that of the historic mines, which is just another factor that is motivating some gem dealers to enhance the quality of the stones.

Acquiring a significant natural ruby, emerald or sapphire gem may seem like a daunting task, but any devoted collector will discover the reward of an exceptional colored stone makes the search worthwhile. In the final analysis, a gem is at its best when it is left as Mother Nature intended.