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FEATURE STORY
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Never out of style, but currently more popular than ever, turquoise is a star with a host of imitators. |
Suddenly the vibrant hues of turquoise are taking the fashion world by storm — yet again. Flashes of bright blue is to be seen everywhere, mixed with silver, amber, coral, jade, and all sorts of media. The color is everywhere, but the stone is not; those bright flashes may be natural turquoise, but also might be any of a number of imitations — glass, plastic, other stones of similar appearance, or even dyed organic matter, such as coconut husks. It is the natural turquoise mineral though, that has withstood the test of time, surging in and out of the fashion limelight like a pendulum, yet never really losing its popularity, just being more popular at certain times than others. From as far back as 6,000 B.C., turquoise has been mined, traded, and revered by ancient cultures in Egypt, Persia, Turkey, and China as well as in the New World, by the Aztecs, Incas, and tribes of the southwestern United States and Mexico.
One of the oldest gemstones known in history, turquoise had the honor of being part of the famous Breastplate of the Hebrew High Priest Aaron, an artifact synonymous with the glory and the mystique of the Holy Grail. Highly considered by Tibetans and Asians as a powerful stone to protect against evil, turquoise was also thought to bring prosperity into the wearer’s life. As a birthstone for December, which carries the zodiac sign Sagittarius, how interesting that Roman and ancient European cultures linked turquoise with horses; turquoise supposedly would protect the wearer from falling from horses, and arrows tipped with turquoise would always hit their mark. Did you know that no English gentleman of the 17th century was regarded as well dressed or well adorned unless he wore jewelry of turquoise? This stone was so highly valued that all 79 of the emeralds in the crown that Napoleon I gave his consort Empress Marie Louise were replaced with Persian turquoise cabochons.
Throughout the centuries, the intense sky-blue Iranian turquoise, known as “Persian turquoise,” has been the most sought after. This is a clear, even blue color with no evidence of green, nor any signs of black veins. As recently as the ‘70s, top-quality turquoise was fetching prices of $2,000 for a 15x20mm piece. Hard to believe. Quality turquoise has also been discovered in the southwestern United States, but prices will probably never reach such highs again due to scandalous misrepresentation of the stone over the years.
Today the term “Persian turquoise” is interpreted more as a description of color quality than an indication of source. Other high color quality terms are “robin’s egg blue” or “sky blue”; in fact, the bluer the color, the higher the value.
OFTEN IMITATED. As with the majority of colored stones, transparent and opaque alike, most turquoise undergoes various enhancement processes, often to stabilize the material. Some methods are accepted, others are seen as deceptive, all are common practices to improve lower-quality stones. Colored plastic impregnation is used to turn nearly white, porous stones blue and improve durability. Wax impregnation seals the pores and deepens the color. Dyeing with black liquid shoe polish is used to imitate matrix. Backing thin pieces with epoxy adds thickness and weight.
Cavities are filled with an epoxy mixed with tiny pieces of yellow metal to imitate pyrite inclusions. Surfaces are coated with lacquer to add color or disguise dyes. All treatments can be detected under magnification, with an acetone swab, or by holding a hot electric needle close to the stone, causing the enhancement to sweat to the surface of the stone. Touching a plastic-impregnated stone with a hot point will give off an acrid smell. Of all the natural substitutes, there are a few common culprits. To distinguish between these and natural turquoise, it is always good to know a bit of gemology. “Gem chrysocolla” is actually a part of the chalcedony group of stones, in which the mineral chrysocolla is finely disseminated, giving the chalcedony an intense medium blue green color. However, the refractive index (RI) of chalcedony is 1.53 to 1.54, much lower than that of turquoise at 1.61 to 1.65. You can test the RI with a refractometer to find out whether it’s chalcedony or turquoise. Whether it’s chrysocolla masquerading as turquoise or the other way around will depend on which is of higher value — at the moment, you’re more liable to see turquoise dressed up as the more valuable chrysocolla.
Amazonite also resembles turquoise and is light green to greenish blue in color with a distinctive mottling and gridlike pattern not seen in turquoise. It also has a refractive index of 1.52 to 1.53, much lower than that of turquoise, and shows an uneven or splintery fracture as opposed to the conchoidal or granular fracture of turquoise. Variscite often has a veined or mottled appearance with a yellowish-brown matrix, a close enough resemblance to have earned the misnomers of Nevada or Californian “turquoise.” However, its refractive reading of 1.56 to 1.59 is much lower than that of turquoise and it will appear pinkish when viewed through a color filter, whereas turquoise shows no color change through a filter. Variscite’s color should be a deterrent in itself, as it resembles that of only poor-quality turquoise.
Howlite is a naturally opaque white stone with a dark, spiderweb matrix appearance, similar to that of turquoise and therefore commonly dyed to imitate the more expensive stone. A quick and easy test to separate the two is a color filter; viewed through a filter, dyed howlite will appear pink or red. Howlite also has the lower refractive index of 1.58 to 1.60 to that of turquoise. As a third test, albeit a destructive one, a drop of hydrochloric acid on an obscure spot on dyed howlite will attack the stone and leave a distinct dull spot. Synthetic turquoise is virtually identical to natural turquoise but will show artificial-looking matrix as well as a distinctive darker blue, spotty appearance on a lighter background, visible under 30 to 50x magnification. This appearance is better known as the “cream of wheat” effect and is a dead give-away. Glass imitations will show a vitreous luster on small fractures as opposed to the waxy luster of the natural stone. Glass and plastic imitations will show signs of tiny bubbles under magnification. Touching plastic imitation turquoise with a hot point will melt the surface and emit an acrid odor.
Another practice, one that can trace its origins back to 2000 B.C., is that of reconstituted turquoise. Known as faience during the Egyptian period, the material consisted of a quartz paste that was shaped, glazed, and fired to resemble sky-blue turquoise. Today, reconstituted turquoise consists of pulverized turquoise rock, mixed with resin and injected into a mold to form a solid brick, which is then shaped. Pulverized pyrite is sometimes added to better imitate natural turquoise. Scary, isn’t it? Don’t despair, though. The best solution is to buy your turquoise from a reputable dealer who won’t hesitate to discuss treatments with you and supply you with a written guarantee that your purchase is nothing else but natural turquoise. Such dealers are out there.
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