Search Colored-Stone.com:

This month's issue

Contact Customer Service

Colored Stone Back Issues

Un-True Blue: Cobalt-Treated Tanzanite Is Here

By David Federman, Editor-in-Chief

For years, jewelers have complained about the paleness of tanzanite in calibrated sizes. Now there’s an avalanche of deep sapphire-blue material. Alas, it’s color-coated.

These two tanzanites were part of a group of stones recently examined at both the AGTA-GTC and AGL facilities in New York. Photo by Fred Kahn and Sun Joo Chung.

There is a positive spin to the bombshell news that tanzanite is now being widely colored-augmented using cobalt coatings -- and Hayley Henning, a publicist for the Tanzanite Foundation isn’t wasting any time finding it. “The use of this treatment,” she says, “only proves how important tanzanite has become.”

She’s right, of course. Just as pork now has the reputation of being “the other white meat” tanzanite now has the reputation of being “the other blue stone” -- the original being sapphire. Indeed, this color-coating technique was first used on corundum back in the 1980s.

This fact puts a second positive spin on the news. The treatment was discovered by two major New York City gem labs -- the American Trade Association’s Gemological Testing Center (AGTA-GTC) and American Gemological Laboratories (AGL) -- working jointly in a very impressive display of gem crisis management.

According to Christopher P. Smith, AGL’s vice president and chief gemologist, the synergy of both labs working together helped them identify the treatment in a matter of days. “The discovery of cobalt-coated tanzanite is a momentous one,” he says. How so, we asked. “It means labs can no longer take any gemstone for granted. Every gem of commercial importance is a candidate for coating.”

This is where the spin turns less positive, even ugly. The gemological Blue Meanies have attacked a sector of the market long thought immune to such an invasion. But this time the Meanies are sucking color from the market by adding, not subtracting, it. And their attack raises issues that are both morally and technologically momentous.

The cobalt coating of the tanzanite produced an iridescence that can be seen when observing the stone’s surface in reflected light. The rectangular area near the point of this facet also highlights an area on the tanzanite where the coating did not adhere. Photomicrograph by Christopher P. Smith.

From a treater’s perspective, cobalt-coated tanzanite is a perfect solution to a problem that has long plagued the tanzanite market: the nagging scarcity of deep-blue tanzanite in smaller sizes. This zoisite usually needs body mass for classy color. But with tanzanite a very popular gem in small calibrated sizes, the market must make do with pale stones -- unless it is willing to accept color coatings.

So far, it has rejected this option with fine gems. But the popularity of coated topaz may have begun to lessen its resistance to gems with electrifying skin-deep beauty.

True, coated topaz colors are exotic and fantastic, even hallucinatory, and in no way resemble the colors of natural topaz. The color of cobalt-coated tanzanite, on the other hand, is not extreme in any way -- just too good to be true. Nevertheless, it gives stones an appearance they might have if natural. Indeed, the New York dealer who first became suspicious of color doctoring had bought parcels of calibrated tanzanite which he was assured were natural except for the customary heating which turns zoisite from brown to blue.

According to a joint AGTA-AGL press release announcing the discovery of cobalt-blued zoisite, the dealer was tipped off to possible coating when he had to repolish a stone and noticed an area of color drop-out. Study of this and other suspect stones under a microscope and in immersion revealed tell-tale signs of coating such as abrasion along facet junctions and culets. Use of X-ray fluorescence, notes Dr. Lore Kiefert, director of the AGTA-GTC, “substantiated the presence of the coating.”

In immersion, it was noted that the color of the tanzanite was lighter along facet junctions and at the culet. This was a result of the coating having been abraded away, revealing the lighter, inherent color of the tanzanite. Photomicrography by Christopher P. Smith.

Pause here to consider the implications of these findings. As the recent scandals in the feldspar market surrounding Asian-origin sunstone make clear, traditional heating is no longer the sole gateway method by which gems in need of color enhancement are prepared for the marketplace. Sophisticated face-lift methods involving diffusion of chemical coloring agents are now as much a pillar of gemstone processing as older, far tamer heat-only methods.

Where does this continuum of high-tech colorization methods lead? How are stones beautified by these methods classified and sold? If surface colorizing using non-intrinsic chemical elements is now a mainstay of gemstone preparation, isn’t it time to develop new categories for this merchandise? Is it enough to say such stones have been color-enhanced?

One thing’s for sure; it is the ultimate sign of tanzanite’s coming of age that this beautiful one-source East African gem may finally force the jewelry industry to publicly question its excessive reliance on cosmetic beauty in a way that sapphire has yet to do.

This was also sent out to our Colored Stone GemMail newsletter subscribers. Want to receive the latest up-to-date information on the gemstone industry? Sign up for our free Colored Stone GemMail newsletter.

e-mail the editors of Colored Stone | About Colored Stone | Sign up for the FREE Colored Stone GemMail newsletter

This site and all of its contents are copyright Colored Stone and Interweave unless otherwise noted.
All articles, photographs, graphics, logos, and trade show floorplans are owned by Colored Stone and may not be reproduced in any form,
in print or in electronic media, without the express written permission of the publisher. Violators will be subject to legal action.