Gemstones & Pearls/Gemology
The new color phenomenon in sapphire that has puzzled the industry for half a year is explained
When an unusual number of orange pink sapphires turned up in the market late last year, questions arose whether they were natural color padparadscha sapphires very rare and valuable or whether the color resulted from treatment. Early testing pointed to a type of diffusion treatment using elements such as beryllium, but questions remained when major labs declined to use the word diffusion.
Since then, lab technicians at Swarovski Co. in Wattens, Austria, confirmed the color in the treated sapphires, which originate mostly from Madagasgar, is due to heat treatment with the gem chrysoberyl, which contains beryllium. The technicians heated sapphire and chrysoberyl together after the companys gem buyer, Yianni Melas, noticed sapphire parcels he bought in Madagascar often contained water-worn crystal fragments of chrysoberyl. The subsequent tests confirmed the connection.
The beryllium obviously comes from the chrysoberyl, says Shane McClure, who has been studying the treated sapphires at the Gemological Institute of America. The reason why this happens is not yet completely understood, but theres no doubt its a form of diffusion, says McClure.
Coming to Terms
Until now labs were reluctant to use the term diffusion because the color-change effects in the gems differed from diffusion treatments seen previously. However, McClure says beryllium diffuses much faster through corundum than other elements, such as titanium. This may account for why the gems in question have diffused color throughout their body rather than just on the surface, which is seen more typically in diffused gems.
In addition to adding an orange component to pink corundum (of which sapphire is one variety), the treatment turns colorless corundum into yellow hues and turns yellowish and greenish corundum into bright, saturated yellow to orange.
Its likely now that most labs will begin to identify these sapphires as diffusion-treated. New descriptions probably will distinguish between this type of diffusion treatment and other types of diffusion.
The GIA Gem Trade Laboratory and the American Gem Trade Association Gemological Testing Center jointly announced at the end of May they will identify the new treatment, which is sometimes also performed on rubies also, as bulk diffusion. After a review of the technical literature and much discussion, the labs concluded this term is scientifically correct and should replace the terms surface diffusion and diffusion treated, which gemologists used previously. The lab reports also will note overgrowths of synthetic material on finished gems when present. These overgrowths sometimes occur with the new treatment.
The discovery that chrysoberyl is the source of the beryllium bulk diffused into these sapphires solved a mystery. After U.S. researchers identified beryllium as the probable coloring agent, Thai dealers and labs protested. They said beryllium, a highly toxic and extremely dangerous element to work with, isnt available over the counter in Thailand, where the gemstones were being treated. The chrysoberyl discovery provided an explanation for the source of the element. Its important to note that although chrysoberyl does contain beryllium, these gemstones are not toxic.
Now that the mystery of how these newly treated sapphires came by their colors has been largely solved, marketplace acceptance will be the next issue. Already, the padparadscha colors are no longer being produced. They simply werent selling and had achieved pariah status. Also the pink sapphires that were being diffused to produce the padparadscha colors are too expensive to waste on a suspect treatment.
Colorless and light yellow and green corundum, however, continue to be treated with the new diffusion process. These gems are not as valuable in their natural form, so the treatment is expected to be accepted more readily.
by Robert Weldon, G.G.
||This 0.85-ct. sapphire originated light greenish in Songea, Tanzania. After a form of diffusion treatment, the color turned bright orange. Courtesy of Allerton Cushman, Sun Valley, ID.
Photo by Robert Weldon.