Hints on Identifying Synthetics and Substitutes
|Synthetic gems have been appearing in the jewelry market with increasing frequency. Here are some hints for identifying them.|
SYNTHETIC SAPPHIRE (ALL COLORS) - If present, gas bubbles will usually be resolved under 30x, although more may be required. They may be present as tiny pinpoints or larger bubbles which, under the Diamondscope, will appear doughnut-like. Highly distorted and elongated bubbles may also be encountered, as well as glassy-surfaced masses of powder that failed to melt.
Low magnification (10x) is usually more effective for resolving curved striae in synthetic alexandrite-like sapphire or curved color banding in synthetic blue sapphire. Detection may be made easier by placing a diffuser, such as a piece of translucent glass or tissue paper, between the stone and the illuminator. Adjusting the darkfield baffle on the Diamondscope to provide a slit of vertical illumination may also accentuate the striae and/or color banding. Refractive index and specific gravity are of no diagnostic value, since these properties duplicate those of the natural.
The spectroscope will usually detect blue, green, and yellow natural sapphire. In addition, ultra-violet fluorescence can be very helpful for distinguishing between natural and synthetic corundum. See Liddicoat's Handbook of Gem Identification for separating colors.
SYNTHETIC RUBY - Same characteristics as for synthetic sapphire. In addition, the synthetic may contain very tightly curved striae and elongated gas bubbles. Frequently, these stones are confused with so-called reconstructed rubies; however, they are usually stones cut from the tips of recently produced boules.
Flux-fusion synthetic rubies are now being marketed. They are characterized by wispy or veil-like inclusions similar to those of the Chatham and Gilson synthetic emeralds. Some show growth lines resembling curved striae. Some material may show natural inclusions due to the natural seed crystal used in their manufacture.
SYNTHETIC STAR CORUNDUM - Ordinarily, once you have seen synthetic star sapphire and star ruby, it is easy to distinguish them from the natural simply by sight. However, this is not always true. Both synthetic star ruby and sapphire possess extremely fine rutile needles that usually require up to 200x or more for resolution. The majority, however, possess typical bubbles and curved striae that are detectable under 30x or in some cases by the unaided eye when viewing stone perpendicular to the base, or apex of the cabochon. The plane in which the striae are oriented is parallel to the girdle of a cut stone; therefore, detection may be difficult, on the more translucent material.
SYNTHETIC EMERALD - At the present time there are two very different types of processes being used to make synthetic emeralds; one, the flux-melt method, of which Chatham and Gilson are the main proponents; and hydrothermal, the process used by Linde. The properties of the Chatham and Gilson vary slightly, and they in turn are different from those of the hydrothermal Linde product. Chatham's flux-melt synthetic emeralds are characterized by a refractive index range in the 1.561 - 1.564 area, and a specific gravity of about 2.65 to 2.66. They float in the specific gravity liquid set at 2.68 unless they happen to have platinum in them, in which case the platinum crystals will be evident under magnification. Many of the Gilson products have similar characteristics, and; like the Chatham, fluoresce a brick red under both short and long-wave ultraviolet light. Some of the Gilsons have the same refractive indices and specific gravities, but fluoresce an orangy-red color. Some of the more recent Gilson synthetic em
The early hydrothermal synthetic emeralds grown by Linde were of a bluish-green color and showed a strong red color to transmitted light. The refractive indices were 1.568 to 1.573 and they fluoresced a strong red color to both long and short-wave ultraviolet light. Later products also fluoresce strong red but not quite to the extent of those grown earlier. The indices are slightly higher with the normal range of 1.572 to 1.578. This synthetic emerald shows no wispy inclusions but is characterized by inclusions that resemble commas. (See handbook of Gem Identification by Liddicoat for photographs showing these inclusions.) In order to identify synthetic emeralds, it is normally necessary to use a combination of refractive index, fluorescence, specific gravity and inclusions.
SYNTHETIC EMERALDS OVERGROWTH ON BERYL - This material is made by growing a layer of synthetic emerald over a faceted or cabochoned colorless beryl. The process is much less time consuming than that required to grow stone-size crystals. Identification is accomplished most easily by suitable immersion liquid of approximately 1.58 - 1.60 R.I. The synthetic emerald overgrowth shows up as a dark green band rimming the stone. The refractive index and specific gravity are both synthetic overgrowth on beryl may show a red fluorescence, but if the layer of synthetic emeralds is very thin, the fluorescence may be weak. Also, due to the strain factor between natural and synthetic material, crazing of the thin synthetic overgrowth will be evident generally.
BERYL TRIPLET - This assembled stone has a beryl top and beryl base with green cement placed between the two. Since the R.I. is the same as that of natural emerald, it might be confused with a natural emerald or a synthetic overgrowth. An immersion test quickly identifies. Bubbles may be seen on cemented surfaces, however, one should be well aware that the beryl surfaces may have natural liquid-filled inclusions.
STRONTIUM TITANATE - This synthetic stone, marketed under the trade name "Fabulite," and sold under a variety of other names, is produced by the Verneuil process. Its refractive index is 2.409, the specific gravity is 5.13 (the highest of any available transparent material), and is slightly refractive with a hardness that varies between 5 and 6. Stones may not contain inclusions; however, gas bubbles are usually present. Numerous surface abrasions and scratches are typical. The stone is also notable for a very high degree of dispersion.
SYNTHETIC RUTILE ('TITANIA') - As with the synthetic star rubies and sapphires, synthetic rutile is in general obvious by sight. If necessary, positive identification can be made as follows.
The refractive index of this synthetic (2.616 - 2.903) is higher than that of diamond. It possesses a strong birefringence, resulting in pronounced doubling of facets when observed through the stone, ore so than any other synthetic or natural stone. The amount of doubling visible through the table depends on the orientation; it can be negligible, if the optic axis is perpendicular to the table. Observed through the pavilion facets, on the other hand, pronounced doubling can be seen. As produced, the stone is usually yellowish, but may be altered to other colors with heat treatment. Orange-blue and brownish-orange colors are frequently confused with zircon. Its specific gravity is approximately 4.26; and its hardness is 6 - 6 ; its dispersion is .3 30.
COLORLESS, SYNTHETIC SPINEL - This material is produced by the Verneuil process, the same as synthetic corundum, but does not display curved striae. Gas bubbles may be absent, even in large stones; when present, however, they may be highly distorted and even appear angular. The refractive index is generally 1.73, which is slightly higher than the average natural spinel, the latter being approximately 1.72. In the absence of gas bubbles, this slightly higher index*, in conjunction with the strong anomalous double refraction and cross-hatched effect when viewed in the polariscope, constitute the typical identifying characteristics of Synthetic Spinel. Under short-wave ultraviolet light, colorless synthetic spinel usually fluoresces moderate to chalky blue and sometimes a strong greenish-blue; under long-wave ultraviolet, it may fluoresce a weak green.
SYNTHETIC DIAMOND - On May 28, 1970, General Electric announced their success in producing cuttable synthetic diamonds up to approximately one carat in size. Those examined in the GIA laboratories ranged from near colorless to fancy blue and canary yellow. The process is extremely expensive, and GE has not indicated any intentions of producing diamonds for commercial gem purposes. However, it is entirely possible that such stones will be introduced sometime in the future. G.R. Crowningshield and his staff at the GIA's New York Laboratory determined that the diamonds initially examined could be separated from natural diamonds. The Summer 1971 issue of Gems & Gemology has an extensive article on the GE synthetic.
Although other synthetic diamonds are being produced for industrial purposes, the minute crystals appear as grayish grains of sand and have no application in jewelry whatsoever.
Y.A.G. (YITRIUM ALUMINUM GARNET) - This material has been produced in a variety of colors. The most common variety is colorless and is currently being marketed as a diamond imitation under a wide variety of names. The refractive index is 1.833; dispersion, .028; Moh's hardness, 8%; specific gravity, 4.55. It is singly refractive.
YNTHETIC TURQUOISE - In 1972 Gibson introduced synthetic turquoise. It has an intense to moderate blue akin to that of fine Iranian material. The refractive index varies between 1.59 and 1.60, and the S.G. between 2.68 and 2.75. The hardness is 6, and the material is available with or without matrix. Upon examination under magnification of 50x or slightly less, the appearance of the surface suggests the presence of millions of tiny spheres individually. An appearance of this nature is not found in genuine material. Also, with material of this quality, if natural, we would expect a spectrum. However, the synthetic lack the natural turquoise line.
SYNTHETIC QUARTZ - This material, produced since the early 1900s for industrial purposes, is now finding increasing popularity in the gem market. It is hydrothermally grown and commonly available in blue, green, purple and yellow. The refractive index, specific gravity, and hardness are no different than the natural. The synthetic material is, in general, untwinned and unstrained. Positive identification is facilitated by inclusions, including small breadcrumbs, 2-phase spicules of gas and liquid, color banding and strain cracks. A spectroscope examination of the blue material reveals one main broad centered near 6500 A.U. with others at 5900 and 5500 A.U. The remaining colors show characteristic spectra.
SYNTHETIC ALEXANDRITE - This synthetic substitute is manufactured by the flux-melt process and marketed through Creative Crystals. Due to the fact that the properties are identical to natural Alexandrite, the key to identification in the inclusions. In addition to the expected flux type veils or wisps, smaller parallel planes of flux and relatively strong straight banding are seen. Also, triangular and/or hexi-angular shaped inclusions and planes of platinum (appearing blackish) may be exhibited. Since the company marketing this product claims that a flawless type is not available, a thorough check with magnification should reveal the true nature of the stone.
SYNTHETIC OPAL - Produced by Gilson laboratories, both the black and white synthetic opals have the same optical and physical properties of the natural. The synthetic is fairly translucent, and depending upon the quality, the play of color can be very vivid. The structure of the latest material is its identity in most cases. The patches of color tend to very mosaic and within each patch is a structure referred to as "wave front" or "reptile skin."
GADOLINIUM GALLIUM GARNET (G.G.G) - A very fine diamond imitation, G.G.G. has a refractive index of 2.030 and dispersion of .038. It has a hardness of 6 and very high S.G. of 7.05. Most materials will be noted to have a frosted girdle and also sometimes show angular inclusions in the form of triangular plates. Minute gas bubbles might also be noted. Fluorescence plays a key in identification at G.G.G. will show a transparent orange to red-orange fluorescence under short-wave ultraviolet which will appear weaker to long-wave, a color not too common to diamond.
DOUBLET - (Synthetic colorless sapphire or synthetic spinel top, strontium titanate bottom). Close inspection should yield a separation plane just below the girdle; high dispersion will be noted as well as the possibility of gas bubbles. See properties for these materials under Comparative Characteristics of Diamond Imitations.
(Garnet top, glass bottom). Because the refractive index can be above the scale that can be read in the refractometer, it can be confused with other diamond imitations. Red ring often observed when examined table down, gas bubbles frequently present in pavilion and at separation plane. Garnet and glass doublets are exceedingly common on today's market, imitating all stones in every color.
'META-JADE', VICTORIA GLASS AND IMORI GLASS - A Laboratory in Japan is producing a particular type of glass that is partially crystallized and provides an excellent substitute for fine green jadeite. This material is so natural looking that most people don't even consider suspecting its origin. If one is aware of it, the identification is quite simple using very ordinary gemological testing procedures. The refractive index and specific gravity of this particular glass is usually around 1.51 and 2.65 respectively, nowhere near the properties for either jadeite or nephrite. Magnification will reveal many gas bubbles (quite spherical but of low relief) and a characteristic structure that is not unlike the appearance of galvanized steel. The fashioned pieces are usually quite thin.
This Imori laboratory is also manufacturing other glasses that are "cat's eye" imitations. For the most part, the colors are quite unnatural, for instance, "turquoise cat's eye" imitation, etc. However, there is one variety that lends itself to an excellent substitution for chrysoberyl cat's eye, especially in smaller sizes. It has an excellent opening and closing of the eye and fine milk and honey effect. However, its RI and SG will separate it easily from chrysoberyl.
SAPPHIRE AND RUBY DOUBLETS - These imitation stones are composed of a crown of natural green sapphire cemented to a pavilion of synthetic blue sapphire or synthetic ruby. Their similarity in appearance to natural ruby and sapphire is striking for several reasons: 1) The stones are usually cut to appear quite "native", that is, usually with a very thin crown and lumpy pavilion; 2) The green sapphire crown usually contains a numerous inclusions (hexagonal growth or color zoning) that is sometimes visible to the unaided eye; 3) The separation plane is at the girdle, the two pieces being cemented together with colorless cement. In some cases, 20x magnification is necessary to see the thin seam; 4) The intense blue or red pavilion is "filtered" through the green sapphire in the face-up position so the colors appear quite natural.
The identification of these doublets is actually quite simple, if one is aware of their existence. Magnification will reveal the natural inclusions confined to the thin crown. In the cement plane and the synthetic pavilion, it's usually easy to see small gas bubbles. Immersion will reveal the separate colors of the individual pieces; the green always confines to the crown, and the intense red or blue to the pavilion. Fluorescence may also be helpful. The synthetic ruby pavilion will fluoresce bright red to lw and sw, and the synthetic blue sapphire will fluoresce chalky blue to sw. The natural green sapphire will remain inert to both lw and sw. It is necessary to remember that fluorescence should be checked in a "pavilion-up" position.
SYNTHETIC CUBIC ZIRCONIA - This material is the best diamond substitute to date. The singly refractive material may appear colorless, or in various colors. The hardness is approximately 8 . The refractive index is approximately 2.15, and the specific gravity is between 5.40 and 6.00. One means of identification is to determine SG by taking a careful hydrostatic reading, or by using heavy liquids. Typical inclusions for synthetic cubic zirconia are tiny "bubblelike" white inclusions, appearing singly, or in rows. Synthetic cubic zirconia will show " a stimulated reaction" on the register of the Ceres Diamond Probe. The specially designed ink in the GIA Diamond Pen will bead, or form a series of beads on synthetic C.Z., while spreading out on a diamond.
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