Contributions to Gemology, On-line GRS Newsletter No.1 21st January 2004 New Sapphire Treatment Producing Colorless Rims Analyzed by LA-ICP-MS by: Dr. A. Peretti *, Prof. Dr. D. Günther ** and F. Mouawad *** (*) GRS Gemresearch Swisslab AG, Lucerne, Switzerland (**) Trace Element and Micro Analysis, Laboratory for Inorganic Chemistry, Swiss Federal Institute of Technology, Zurich, Switzerland. (***) Precious Link Ltd. In late 2003, a new treatment of sapphires appeared in the market producing colorless rims. The question arised, whether this treatment involves: a.) Synthetic overgrowth b.) Diffusion of chemical elements c.) or whether the treatment corresponds to a conventional treatment or not. In late 2003, Dr. A. Peretti made an expedition to the source of this new material in Sri Lanka to collect the material for research, and Fred Mouawad of Precious Link Ltd. assisted by providing a 5 ct sapphire that corresponded to the new sapphire material. This gemstone together with a series of samples collected at the source were supplied to the Swiss Federal Institute of Technology. The lab of Prof. Dr. D. Günther made further scientific analyses with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Each sample was cut in half and approx. 300 LA-ICP-MS analyses were carried out in two profiles across the sample (see chart 1 and 2). Each of these measured points were analyzed for 40 different elements, namely: Li, Be, B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Rb, Sr, Y, Zr, Nb, Mo, Sn, Sb, Cs, Ba, La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Pb, Bi, Th and U. Furthermore, the core and rim of the newly treated sapphires were investigated by microscopic techniques by Dr. A. Peretti and Fred Mouawad (see images). Total of approximately 12,000 data points were collected (examples see charts 1 and 2). Results The microscopic analyses showed that the silk inclusions were dissolved into oriented points due to heat treatment (see Image 6). Natural zoning patterns were extending from the core to the rim (Images 3 & 4). They were not terminated at the core to colorless rim interface (Image 5). The natural growth zoning could be clearly followed to the edge of the sapphires independently of the colorless rim effects (Image 4). The chemical composition in the sapphires including all the different elements measured as listed above did not show any clear differences between the core and the rim. Particularly, no increase in Magnesium (Mg), Lithium (Li), Beryllium (Be), Boron (B) and other light elements were found. It reflected typical chemical compositions found in natural sapphires. Also no differences in other elements such as Ti, Fe or V were detected. Differences in OH-groups (due to hydrogen diffusion) or Nitrogen (N) in the corundum lattice are now being currently measured. The pattern of the chemical elements across the sapphire reflect differences due to growth in the sapphire (Chart 1) and in one profile (Chart 2), the element concentrations were decreasing toward the rim. More statistical analyses to confirm this observation are currently being investigated by GRS and Prof. Dr. Günther at the Swiss Institute of Technology. Further confirmation on another sample is shown in Chart 3. The conclusion at this point of the research can be made as following: - no synthetic overgrowth was found - no diffusion of the light elements Lithium (Li),Boron (B), Beryllium (Be) and Magnesium (Mg) were found. Further analyses of the interaction of other gases (Nitrogen, Hydrogen, Oxygen etc.) with sapphire, used in the heat-treatment process are being finalized. The results will be published in our forthcoming journal 'Contribution to Gemology' Issue No. 3.
	Image 1: Heated Natural Sapphire of over 5cts with colorless rim as viewed from the girdle side (colorless rim present but not visible in this illumination)
	Image 2: Heated Natural Sapphire of over 5cts with colorless rim as viewed from the girdle side.
	Image 3: Heated Natural Sapphire of over 5cts with colorless rim as viewed from the girdle side (colorless rim present but not visible in this illumination).
	Image 4: Heated Natural Sapphire of over 5cts with colorless rim as viewed from the crown showing growth zones and dissolved silk zones extending to the rim (colorless rim present but not visible in this illumination).
	Image 5: Heated Natural Sapphire of over 5 cts with colorless rim in combined reflected and transmitted light. Illumination shows zoning (colorless rim) produced by the new heating technique and original growth zoning. Dissolved particles extending from the core to the rim following a zoning perpendicular to the border line between core and colorless rim (see enlarged picture).
	Image 6: Enlarged magnification of particles produced by heating (dissolved rutile needles). Blue halos are associated to these dissolved particles and can be seen if illuminated in transmitted light.

Chart 1 and Chart 2: Internationally first chemical analyses of the sapphires heated with new heating technique producing colorless rims. Section across a heated sapphire showing a colorless rim analyzed by LA-ICP-MS. Selected chemical elements are graphically shown (in ppm). Note that no abrupt changes occur from the core towards the rim (Chart 1 & Chart 2). The typical chemical elements of a natural sapphire are present (Ti,V, Mg, Fe, Ga), both in the core and the rim in similar concentrations. No detection of additional light elements such as Boron (B), Beryllium (Be) and Lithium (Li) are found. Chemical variations are mostly related to growth zoning in the parent natural sapphire material.
Chart 3: Internationally first chemical analyses of the sapphires heated with new heating technique producing colorless rims. Section across a heated sapphire showing a colorless rim analyzed by LA-ICP-MS. Selected chemical elements are graphically shown (in ppm). Note that no abrupt changes occur from the core towards the rim. The typical chemical elements of a natural sapphire are present (Ti,V, Mg, Fe, Ga), both in the core and the rim in similar ratios. No detection of additional light elements such as Boron (B), Beryllium (Be) and Lithium (Li) are found. A general decrease of all the element concentrations was clearly seen from the core to the colorless rim of the sapphire.