corundum, Burma.12, USA.12, North Carolina.12, gems

More on Czochralski “pulled” synthetic sapphires. The Spring 1993 and Summer 1994 Gem News sections contain entries on Czochralski-pulled synthetic sapphires seen at the 1993 and 1994 Tucson shows. All the colors mentioned in those entries—including blue—were again seen at the 1995 shows. According to one vendor of this material, Gerry Manning of Manning International, New York, the pulled synthetic blue sapphire crystals are unevenly colored. The first-grown portions of the rod-shaped crystals are lightest in color; the rods become increasingly darker toward the opposite end (the last part to crystallize). The color zoning described by Mr. Manning differs from that seen in split boules of flame-fusion synthetic blue sapphire. There, the color is typically lightest in the center and progressively darker toward the periphery. Mr. Manning provided two faceted blue specimens (figure 20) for gemological characterization. Properties determined were: R.I. – nₚ = 1.760; nₒ = 1.768; birefringence ≈ 0.008; S.G. (determined hydrostatically) ≈ 4.0 to 4.01. Both specimens were inert to long-wave UV and fluoresced a weak, chalky bluish green to short-wave UV. All these properties are similar to those of flame-fusion synthetic blue sapphires. We also noted weak red fluorescence to intense transmitted light from a fiber-optic light source, and the samples appeared faintly pink through the Chelsea color filter. These latter two reactions have been noted in some violetish blue flame-fusion synthetic sapphires that contain traces of chromium, as well as in some natural blue-to-violet sapphires from Sri Lanka that also contain traces of chromium. Magnification revealed minute gas bubbles in both samples. Unlike flame-fusion synthetic sapphires, however, although the color of our samples did not appear totally uniform, we could not resolve curved color banding using diffused transmitted light and magnification. Only when this lighting technique was combined with immersion of the samples in methylene iodide could we see wide, slightly curved blue banding, which is proof of synthesis.