The bulk of bulk diffusion is identifiable say the labs

The Gemological Institute of America’s Gem Trade Lab (GTL) and the American Gem Trade Association’s Gem Testing Center (GTC) have announced progress in the identification of the new bulk-diffusion-treated sapphires coming from Chanthaburi, Thailand.

In a teleconference with the trade press, Tom Moses, vice president of gem identification for GTL in New York; Shane McClure, director of gem identification services at the GTL in Carlsbad, Calif.; and Ken Scarratt, GTC’s director in New York, said gemologists should be able to identify much of this new material with standard gemological tests.

But it won’t be easy. Gemologists will have to consider all the indicators, using magnification, immersion, and possibly visible spectrum. These indicators can be extremely difficult to find. “We’re looking for color distribution, primarily,” says Scarratt. “Surface conformal zoning. We do see this in a lot of these stones.”

This zoning is similar to, yet different from, the old blue diffusion-treated sapphires. In the old treatment, the color layer, now called “surface conformal zoning,” was shallow and readily visible under immersion or in diffused lighting without immersion. But this layer is much more difficult to find in the new stones, even under immersion. “In some cases, the color zoning is really quite deep, but it is still there,” says Scarratt.

Heated inclusions may also be indicators. “We’ve seen some rubies that this procedure has been done to,” says Moses. Color zoning in ruby is more difficult to see than in the yellow or orange sapphires. Moses suggests that gemologists look for evidence of high heat. “Look for inclusion scene that suggests extreme conditions, where inclusions have been strongly altered,” he says.

The visible spectrum might offer clues, and other gemological tests also are being investigated. Infrared spectrum analysis may be useful in finding an indication of treatment, says Scarratt, who noted that infrared is “standard gem testing equipment” for the professional gem lab.

When all else fails, the stones can be identified by secondary ion mass spectrometry (SIMS), but it’s an expensive option. “Stones that cannot be identified by normal gemological tests are those stones in which the color goes right the way through,” says Scarratt. “For example, there are certain inclusion scenes, [even without seeing the conforming color layer], that would help us conclude that bulk diffusion treatment was carried out.” Moses notes that even some hint of surface conforming color zoning may not be conclusive enough to allow a determination of bulk diffusion. “Those are the situations that create an identification challenge,” he says. In such cases, and also when there are no inclusions, labs use SIMS analysis to look for the coloring agent—beryllium.

The beryllium factor. Using detailed analyses and replication experiments, GTL and GTC (with the aid of John Emmett at Crystal Chemistry in Brush Prairie, Wash., and others) have concluded unequivocally that diffusion of beryllium is the single causative agent of color change in this new process.

In effect, beryllium adds yellow to the stone. Adding yellow to a pink sapphire produces pinkish-orange—padparadscha. According to the labs, the technique produces yellow, orange, orangey-pink, orange-red, green, green-blue and violet, all of which are now present on the market.

SIMS analysis can cost $500 to $700 or more per stone, depending on how many samples are taken. Labs sometimes pick up the tab because it adds to the identification database. Other times, the client is able to pay for the testing. SIMS testing equipment costs $1.5 million to $2.5 million, McClure estimates.

Calling it bulk. “All of the credible labs in the world agree that this is a bulk diffusion process,” says McClure. “But there’s still disagreement, in some of the markets, as to exactly how they’re going to say it on their laboratory reports.”

GTL and GTC both identify this material as natural corundum; ruby or sapphire, depending only on the color; and that “evidence of heat treatment and a surface-related color zone created by bulk diffusion are present.” The new beryllium bulk diffusion is similar to titanium diffusion used to create blue from colorless sapphire, so both will be described as bulk diffusion. Other versions of the identification nomenclature will include the phrase “areas of synthetic overgrowth have been detected.” That refers to recrystallization of melted outer surface layer that is not polished off.

What do you call a gemstone that’s part natural, part synthetic? “There’s definitely a point where so much has been done to the stone that perhaps it should be treated differently,” notes McClure. “We don’t know the answer to this yet. But it’s something we’re thinking about.”

How much is out there? Scarratt estimates that as much as 5% of the sapphires his lab sees are bulk diffusion treated, but labs get mostly high-value stones that aren’t subjected to this process. After sight-identifying gems through the glass of showcases at trade shows, Scarratt and Moses estimate “significant amounts” have been produced. “It appears that the scope of this may be more significant than we thought a few months ago,” says Moses.

According to GIA, the establishment of identification criteria is being given the highest priority at both the GTL and GTC. They say it’s their hope that their efforts will help allay the concerns of dealers and jewelers regarding bulk-diffusion-treated sapphires and that their expertise in gem identification will allow consumers to purchase corundum with certainty and confidence.