Hänni Addresses Bulk Diffusion

Sapphires subjected to the bulk diffusion treatment developed in Chanthaburi, Thailand, had levels of beryllium far higher than natural or traditionally heated sapphire, according to research conducted by Dr. Henry A. Hänni, director of the SSEF Swiss Gemological Institute in Basel, Switzerland. Beryllium levels were noticeably higher at the gem’s outer edges, but even the center of the stones showed levels of beryllium not found in unheated sapphires. (The beryllium comes from rough crystals of chrysoberyl, which are heated with the sapphire.) Hänni, who presented his research results in Chanthaburi, says, “I felt it was important to present these findings here first, as this is where this development is taking place.”

The Bangkok Post reported that “the Gem and Jewellery Institute of Thailand conducted its own research while the Thai Gem and Jewellery Traders’ Association (TGJTA) hired GRS Swiss Lab to conduct research on the process of coloration. Finally, it was agreed that there was beryllium in the stones but the substance by itself could not produce the color. The beryllium, however, may be a catalyst for the complex color-causing mechanism [involving] certain trace elements [already within] the stones.”

Hänni notes that the diffused beryllium is able to penetrate to great depths within the stones. In the old blue surface-diffusion treatment, coloring agents penetrate only the outer layer, and the diffused color is lost when the stone is recut. For this reason, the older treatment is performed on faceted gems, whereas the newer method with deep penetration also is performed on rough.

Whether the added color is confined to the surface or penetrates throughout, labs such as AGTA’s Gem Testing Center and GIA’s Gem Trade Laboratory are identifying this material as “bulk diffusion treated.” However, according to the Bangkok Post, “a [Thai Gem and Jewelry Institute] official said that if the color of the whole stone was changed and the institute was certain that the color was created by the new technique, its certificate would indicate that the stone was a “natural corundum with an indication of heating” and that its color was “partially caused by a stable color center.”

In related research, Dr. John Emmett and Troy Douthit of Crystal Chemistry in Brush Prairie, Wash., have changed colorless sapphire to yellow using high-purity beryllium oxide powder instead of chrysoberyl. Emmett, a member of the AGTA-GTC’s board of governors and an expert in corundum enhancement, was able to recreate all of the padparadscha, orange, gold, and yellow colors. Emmett writes, “Thus it is quite clear that the beryllium diffused into these stones in an oxygen atmosphere is the single causative agent in the color changes.” For more information on Emmett’s study, log onto AGTA’s Web site at www.AGTA.org.