In many cases the standard tests for identification of a gemstone will preclude the necessity of an enumeration of its inclusions, since so few gem species are synthesized. Differentiation between genuine and synthetic stones, however, depends upon the jeweler's ability to recognize inclusions characteristic of each gem. Since synthetics are quite common on the present market, the value of a sound knowledge of the characteristic inclusions of gemstones is emphasized, for the jeweler is frequently called on to distinguish between a genuine and a synthetic stone.
The many important gems made synthetically have characteristic differences under high magnification. Although inclusions commonly found in synthetic corundum, spinel and emerald are discussed on the page of synthetic gemstones, they are or such important to the jeweler in identifying gem; that it is well to describe them here as well.
FLAME-FUSION SYNTHETIC CORUNDUM
Spherical gas bubbles are characteristic of synthetic corundum and may have the following appearance and arrangements : (FIG 28 & 29).
They maybe round in crass-section, but elongated, like a bubble that has risen from its original position in a molten material.
They may be found in groups of many tiny bubbles, frequently with one or two large bubbles in addition, or as rough lines of bubbles arranged on a curve.
Curved growth lines or striae, are often evident in synthetic corundum, and are characteristic. However, they are not seen in yellow, orange or colorless synthetics.
CAUTION: Since polishing marks on a facet may resemble striae, be sure to focus the microscope on a point within the gem when observing the stone for curved striae, and be certain that the striae continue across several facets.
FLUX-GROWN SYNTHETIC RUBY
Both Carroll Chatham and Kashan Laboratories of Texas are marketing synthetic rubles grown by flux techniques. Gilson is a third manufacturer.
Early individual crystals offered by Chatham were characterized by lame natural seeds. Seeds were not noted in the darker red faceted stones and cabochons. Both Chatham and Kashan synthetics may have (FIG 30) veil like or wisp like inclusions, similar in appearance under low magnification to flux-grown synthetic emeralds. There are usually coarser flux inclusions and smaller tubes, giving the appearance of dashed lines (FIG 31). Occasionally, a thin tube resembles coarse silk (FIG 32).
Spherical gas bubbles, usually very small and quite widely separated, rarely grouped, are characteristic of synthetic spinel.
Small inclusions that have the appearance of white bread crumbs in illumination also characterize synthetic spinel, but are less commonly encountered. (FIG 33)
Very rarely curved color bands are visible in synthetic spinel, but never curved striae in any color but red.
Synthetic spinel often contains inclusions that have a deceptively natural appearance. Larger gas bubbles often have a distinctly angular outline. Threadlike gas inclusions are common.
Fortunately, there are other means of separation; also, minute spherical gas bubbles almost always accompany the deceptive types of inclusions. (FIG 34)
Synthetic emerald is distinctly different from either synthetic spinel or synthetic corundum in that it contains no spherical bubbles and never has curved growth lines. There are now several distinct typos of synthetic emeralds available. The flux-fusion type, such as those manufactured by Chatham, Gilson and Zerfass, is distinctly different from the hydrothermal type made by Linde. The hydrothermal overgrowth of synthetic emerald on pre-faceted natural beryl made by Lechleitner is different from either.
The inclusions of the flux-fusion products have a deceivingly genuine appearance. Indeed, the Chatham, Gilson and Zerfass.