The Beryllium Treatment of Fancy Sapphires with a New Heat-treatment Technique (Part B).

by Adolf Peretti (*), Detlef Günther(**) and Anne-Liese Graber (**)

(*) GRS Gemresearch Swisslab LTD, Switzerland
(**) Institute of Chemistry, Swiss Federal Institute of Technology, Zurich, Switzerland.

Introduction
The new heat treatment of corundum is a technique that involves extremely high temperatures, oxidation conditions and diffusion of Beryllium into the corundum's surface (Peretti and Günther, 2002, Hanni and Pettke, 2002, Emmet et al., 2003). Part A of this study (Peretti and Günther, 2002) concentrated on the interaction of Beryllium with the parent chemistry of natural fancy sapphires and other gemological aspects. It was noticed that only very minor concentrations of Beryllium were present in the treated sapphires. This data was confirmed later by Hanni and Pettke (2002). As mentioned earlier, the understanding of the direct contribution of Beryllium to the color of these treated natural sapphires needed additional research (see Peretti and Günther, Contributions to Gemology 2002, vol. 1, page 39). As pointed out in a recently published article on this new treatment (Emmett et al., 2003), the understanding of the new treatment needs more precise data on various trace elements that are not yet available in world literature. In part B of the characterization of the new treatment, we provide extended chemical analyses of natural and synthetic materials, including sapphires, and test the models proposed by Emmett et al. (2003).

Materials and Methods
The studied materials include synthetic materials from various manufacturers. Colorless synthetic sapphires were from watch glass producers in Switzerland, synthetic pink, orange and yellow Verneuil sapphires were obtained from Djevahirdijan SA (Monthey, Switzerland), and synthetic hydrothermal rubies were from Novosibirk (Russia). Further natural samples are listed in Tab. 6 of Peretti and Günther (2002) and additional samples of rubies and blue sapphires were collected in the market in Bangkok (see Tab. E2 and E3).

Samples were prepared with rough, as well as faceted materials, and cut in half. One piece was kept untreated for reference ("reference samples"), and one half piece sent for commercial Beryllium treatment with the new method to a specialized commercial factory in Chantaburi (Thailand). The heating experiments were reportedly carried out at very high temperature near the melting point of corundum under high oxidation conditions, including Beryllium diffusion. Details of the method remain the intellectual property of the factory. After the Be-treated samples came back from Chantaburi, untreated and treated samples were compared and color changes investigated (E1, E9 and E13). The treated samples were cut in half for further chemical and spectroscopic analyses (e.g. Fig. E5). Further samples of natural blue sapphires, fancy sapphires and rubies have also been Beryllium-treated by the same factory as well as by another factory in Bangkok. For comparison, additional natural orange sapphires were investigated which were heated by conventional methods (Tab. E3). The samples were measured for chemical composition by LA-ICP-MS (see Guillong and Günther (2001)), for origin of color by UV-VIS-NIR-Spectroscopy, and for structural/chemical analyses by Cathodoluminescence.

Cathodoluminescence Analyses (CL)
The analyses were carried out by Prof. K. Ramseyer at the University of Berne, Institute of Geological Sciences, Berne (Switzerland). The same methods were applied as described by Ramseyer K. (2002).