Irradiated Diamond

The diamond market is the gem world’s last bastion of prissiness about gemstone treatment.

Whereas colored stone dealers have faced such facts of life as heating, irradiation and impregnation, and pearl dealers long ago made peace with culturing, diamond dealers still seem to be grappling with the realities of enhancement. A case in point: irradiated diamonds. Most specialists in fancy (natural) color diamonds won’t buy or sell stones known to have been irradiated—although these stones have been marketed for more than 50 years. As a result, irradiated diamonds are pretty much segregated from the mainstream and are sold exclusively by a tiny number of dealer-devotees.

The persistence of such separatism is ironic because diamonds were the first gem to be colorized in the lab with radiation. In 1904, British scientist Sir William Crookes set out to prove they could be tinted in this manner by burying small stones in radium bromide salts.

Although he succeeded, Crookes’ methods left something to be desired since diamonds turned a skin-deep green only, took months to do so and became radioactive in the process (something they remain to this day). But when, 38 years later, stones were greened more than superficially over days in a Michigan cyclotron without becoming radioactive for more than a few hours afterward, the stage was set to color diamonds in a safe, fast, permanent way. Now someone had to find out how to create a wider palette of colors. By coupling irradiation and heating, research gemologists began producing green, blue, yellow, brown and black diamonds on a commercial scale in the early 1950s.

The influx of varied-blue irradiated diamonds provoked as great a furor in the jewelry trade as the influx of cultured pearls had done some 30 years earlier. Then when the spreading contamination of natural pearl habitats in the 1950s and 1960s created increasing scarcities and drove up prices, trade acceptance of the cultured variety became a matter of economic necessity. With demand for fancy color diamonds the greatest in history, and their prices at all-time highs, economic necessity could finally give irradiated diamonds their greatest opportunity for broad acceptance.

Fooling the Eye

Although irradiation produces just about every diamond hue found in nature, it does so with varying degrees of success. Natural and treated golden brownish-yellow stones (possessing a color dealers call “burnt orange”) can’t be told apart merely by sight.

The same holds true for stones GIA would grade as “Fancy intense,” the lab’s highest color rating for fancy yellow diamonds. In 1992, some unscrupulous dealers took to submitting borderline “fancy-intense” stones to GIA which they gambled would eke out that grade. Those that did were zapped to deepen color and heighten value, then offered for sale as top-notch all-natural yellows. Luckily, labs caught their artificial coloring.

Recent scams involving undisclosed irradiation of yellow and also green diamonds recall the most famous diamond scandal of modern times involving a mammoth natural yellow stone called the “Deepdene,” whose color was deepened several shades by irradiation without disclosure of this fact. In 1971, this 104.52-carat stone was sold by Christie’s Geneva for about $1.2 million. Although the stone’s color was pedigreed of natural origin, spectroscopic examination showed a telltale 5940 absorption line—proof of irradiation since its discovery by GIA’s Robert Crowningshield in 1956.

Why did the stone’s consignor, a world-renowned jeweler, fail to reveal the treatment? “At the time,” Crowningshield explained charitably, “many believed that color in diamonds was due to radiation. So putting stones in a cyclotron, it was argued, did what nature would have done anyway. Today, of course, we know yellow in diamonds is caused by nitrogen.”

Anyhow, the nearly identical color of natural and irradiated yellow diamonds makes a good case for the latter, especially after factoring in the enormous price differentials between the two.

A Blue Less Blessed

If not for the additional step of heating, performed during or after irradiation, colored diamonds would come in just two hues: green and blue. Moreover, the blue almost always shows a strong accent of green, giving it a zircon-like color that, as far as we know, is never found in nature. Indeed, even blue zircons own their color to heating.

Unlike treated diamonds, natural blue diamonds have a color that usually veers toward gray instead of green. Because of this basic color dissimilarity, it doesn’t make sense to quote price comparisons—whopping as they are. Curiously, while the blue of irradiated diamonds is a novelty color, it is probably the most popular of all irradiated diamond hues and can command more money than any other regularly available treated diamond color.

Price comparisons between natural and treated green diamonds are also impossible to make. But here the reason has to do with the fact that there is as yet no sure-fire way to positively identify the color origin of many green diamonds—since color in both is the result of irradiation. In 1989, scores of dealers brought irradiated pistachio-green diamonds as natural (for tens of thousands of dollars per carat) simply because their color was so unlike that of the typical irradiated green diamond. Then labs burst the bubble.

While such scams don’t improve the reputation of treated diamonds, their pariah status still strikes us as undeserved. For, on the whole, the disclosure record of irradiated diamond specialists is exemplary.

An irradiated blue diamond courtesy of Nice Diamonds, New York.

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