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Center-fused Color Treated Gemstones
Earlier this year a new gem treatment was introduced. Developed by Sithy Gems and Lapidary, (www.supergreentopaz.slt.lk,) in Sri Lanka, it is a new twist on enhanced gems. They call it “center-fused color treatment,” which at first sounds confusing. However, a little knowledge and it becomes simple.
by Donald Clark CSM IMG
What It Is
The treatment is done in two steps. First, a layer of diffusion treatment color is applied to a piece of colorless rough. A second piece is then fused to the colored piece using high temperature and high pressure, (HTHP.) This leaves the color layer on the girdle plane.
The end result is a single stone with extraordinary color. Unlike surface treated gems, the color will not scratch off and is unaffected by chemicals or the heat of a torch.
Since this technique is so different, many people are confused as to how they should be classified. Yes, they involve multiple techniques, but they are simply classed as an assembled stone.
The most notable feature of the center fused gems is the color. Not knowing the source, the blue green could be confused with Paraiba tourmaline, the red and orange with cherry opals, etc. However, a standard examination will quickly tell you that the material is either quartz or topaz.
The refractive index, optic sign, and specific gravity are identical to other quartz or topaz. However, since these are created with natural gem material, identification by inclusions can be tricky. The center fused gems are cut from very clean material, but they do show natural inclusions in the microscope.
The keys to identifying center-fused gems are found with a loupe. The most visible feature is what at first looks like a fingerprint inclusion. This is best seen under the girdle, as it is difficult to see from the crown. With care, you can see that it is actually just visible where light is striking it. If you move the gem in relationship to the light source, the “fingerprint” will move as well and it is always parallel to the girdle plane.
With higher magnification, you can tell that it is a series of small bubbles in a plane under the color layer. The bubbles could lead one to believe it is a synthetic, but again these are made from natural gem materials and are properly classed as an assembled stone.
The final identifying feature is found on the girdle. The color line is distinct even in air; you do not need immersion as you would with a glued doublet. It also has significant thickness, about .1 millimeter. This and the movable "fingerprint" are easy ways to distinguish them from glued doublets. Natural inclusions reinforce this observation.
Sithy Gems and Lapidary should be complimented for their ingenuity. They have created a stable method of color enhancement that rivals the brightest diffusion treated gems. In addition, they pride themselves in fine cutting, so the gems have all the brilliance and scintillation one would expect from a high end gemstone.
Overall, these are very fine appearing gems. Considering their reasonable price, you can expect them to find wide acceptance in the market.
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