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Treated Sapphire. Like ruby, sapphire is the mineral corundum, and thus the treatments used on sapphire are frequently the same as those used on ruby. The microscopic evidence is also nearly the same. Heat treatment The most common enhancement to sapphire is heat treatment. We consider every sapphire we deal with to be heat-treated unless we can prove otherwise. (The sapphire in figure 5 is untreated, indicated in part by its intact silk.) Like ruby, heat-treated sapphires show broken silk, exploded crystals, melted inclusions with stress fractures, pitted girdles, and double girdles. Sapphires also tend to show discoid fractures due to heat treatment. These are circular, highly reflective breaks in the stone that are often surrounded by a textured edge. Ruby also shows this characteristic, though it seems to us more common in sapphire. Diffusion treatment Common in sapphire, but not nearly as prevalent as heat treatment, is traditional diffusion treatment, in which a colorless or very light faceted sapphire is heated to nearly melting in the presence of titanium and iron. This results in a very thin layer of colour on the faceted stone's surface, which is rippled as a result of the high temperatures and must be repolished. Repolishing leaves thicker areas of the color layer on facet junctions (figure 6). Concentrations of colour also occur in and around surface reaching inclusions. Microscopi-cally, this becomes evident using diffused light from beneath the stone. By contrast, most natural sapphires viewed in this way show the typical hexagonal colour banding. Diffusion induced star sapphires can be found on the market in small numbers. These are tricky to identify using a microscope. The most noticeable characteristic is that the star seems to be confined to the surface of the stone and there is a lack of needlelike structures to account for the star's presence deeper within the stone. A new variation on diffusion treatment has entered the market recently and has caused an uproar among jewelers, especially in the yellow, orange, and pink colours. In this version of diffusion treatment, beryllium is the chemical heated with the sapphires. (Occasionally, rubies are also treated in this way.) The treatment is often undetectable using standard gemological testing. However, there are a few clues in microscopic appearance that may be helpful. Since high heat is used, the inclusions in beryllium-diffused sapphire often have an appearance that can include melted crystals. Recognizing these particular characteristics takes practice and training. (The Gems and Gemology Summer 2003 issue has a fabulous picture reference of indicative inclusions for this form of treatment.) Also, if the stone in question is observed in diffused light while
immersed in a heavy liquid such as methylene iodide (water or wintergreen
oil can be used with less success), a light layer may be visible around
the stone. This clue is not totally diagnostic, as stones subjected
to this type of diffusion treatment may be penetrated completely by
the treatment and thus not show a layer of colour. When in doubt,
especially with expensive stones being sold as Padparadscha, it is
best to have them tested by a laboratory.
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