The buzz in opal today is for gemstones from a new source in Ethiopia, discovered in 2008 near Wegel Tena, Wollo Province. The mine produces mostly white, translucent opal, much of which has vivid play-of-color. Researchers and some wholesalers in the gem trade hail the deposit’s significant quantities of high-quality play-of-color opal that is remarkably stable and durable. But other specialized opal dealers remain skeptical that this high-porosity, high-water-content hydrophane opal may in time crack or craze, which would endanger consumer confidence in opal and opal jewelry for the future.
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A gem like no other, opal is an amorphous form of silica related to quartz that contains a variable amount of water and often is very brittle and fragile. “Opal in general is prone to break; it’s basically a glass of sorts,” explains Bear Williams, director, Stone Group Laboratories, Jefferson City, Missouri.
Opal is typically found in two geologically distinct environments: sedimentary or volcanic. Australia is the leading producer of opal, with more than 90 percent of the world’s supply. It is considered an important source of precious opal, which is produced in a sedimentary environment and has a proven track record of stability. The only other significant opal producers are Brazil and Mexico, and most recently Ethiopia — all volcanic environments. Fire and crystal opal, found in Mexico and the United States, is also of volcanic origin.
The Research
Opal from Ethiopia that hit the market in 1993 from deposits near Mezezo, Shewa Province, has a tendency to craze. But the Wollo Province deposit was hailed as one of the most promising deposits of precious opal for the coming years in the Summer 2010 issue of Gems & Gemology and the Summer 2011 issue of InColor. “Wollo opal should be recognized as a new type because it can absorb or lose water, affecting transparency and play-of-color when wet, but recovering all its qualities when dry,” report researchers. They describe this new Ethiopian opal find as different from the opals of Shewa Province. Laboratory testing of the Wollo opal revealed most specimens were resistant to crazing after repeatedly being immersed in water and dried out over a period of time. Not only are they stable, researchers say, they’re surprisingly tough.
According to Gems & Gemology, “Wegel Tena opals could sustain a fall from [over three feet] onto a concrete floor with no visible damage, even under the microscope. Repetition of the test on five oval cabochons did not produce any sign of damage.” When the same experiment was conducted with oval cabochons from the Mezezo deposit and Australia, including one boulder opal, all samples broke.
Mike Romanella, partner in Commercial Mineral Company, Scottsdale, Arizona, notes that although the Wollo opal does not have the 100 years of proven history the Australian opal has, his two-year experience with the material has been positive. “We’ve seen little crazing in the tens of thousands of pieces we’ve worked with, and we’ve had no returns from our customers.”
Frank Farnsworth, president of Idaho Opal & Gem Corp., Pocatello, Idaho, agrees that the Wollo Province opal is interesting from a scientific point of view, but his concerns outweigh his fascination. “My concerns are based on the material being hydrophane and therefore losing color when submerged in water, with the possibility of the color not coming back or picking up dyes and lotions that will taint the base color of the opal,” Farnsworth explains. “Also, I’m concerned with the amount of drying and cracking from this material and its long-term durability.”
Smoke Treatment
In addition, researchers have identified yellow-to-orange fire opal and crystal opal from Wollo Province as being more prone to breakage than the white opal from the same province. Another concern is that some of the crystal opal produced at the deposits in Wollo is being darkened via a smoke treatment to resemble natural black opal. In fact, Jewelry Television submitted samples presented to it as a new find of Ethiopian natural black opal to Stone Group Laboratories for testing.
The stone “turned out to be color enhanced using an older method, but certainly a new method for the Ethiopian hydrophane material,” says Williams. “The nature of hydrophane allows this treatment to deeply penetrate the stone, yielding even body color.” In his stability tests, Williams found that the opal from Wollo that is “widely sold as nice crystal opal is also tough and stable enough to be treated with smoke and heat and not craze. After treatment, I dropped a smaller, round Wollo opal from seven feet onto a hard tile floor. Most opal, including Australian, would crack; even a diamond might cleave, but this thing bounced back without damage.”
Gemologists and appraisers can sight-identify opal that has been color enhanced by smoke treatment once they’ve seen a few examples, says Williams. This new smoke-treated material exhibits fair to bright play-of-color with flashes of red and green patterns, consistent with the play-of-color opals from Wollo Province. However, Williams says the black body color is not convincingly natural in appearance.
“Black opal is the rarest and most desirable color of opal, as a dark body color sets off an opal’s play-of-color more dramatically,” says Williams. “A few places produce natural colored black opal, most notably Lightning Ridge, Australia, and Mintabie in South Australia.” There’s been no natural black opal reported from Ethiopia.
The Market
The recent InColor report measures opal production from Wollo Province at tenths of a kilogram in 2008, hundreds of kilograms in 2009 and thousands of kilograms in 2010. The Ethiopian Ministry of Mines claimed more than $4.4 million was obtained from the exportation of 14,000 kilograms of opal over the past 11 months. Twenty-seven countries are reportedly buying Ethiopian opal, with India, China and the United States leading customers. “Indian dealers are purchasing large quantities of opal rough and cutting it in Jaipur,” says David Ratliff, Ratliff Opal Pty. Ltd. in Cairns, Australia. Cutters in Bangkok and Malaysia also are working with the goods, according to Farnsworth.
Williams says that with the introduction of Ethiopian opal into the equation, sales of opal carats worldwide have nearly doubled in the past couple of years. He noted that there is a much bigger awareness and appreciation of opal these days.
Dealers say the Wollo Province opal, compared to similar white play-of-color Australian goods, is selling at steep 30 percent to 50 percent discounts, according to Farnsworth, who notes a wide range of prices, from less than $1 a gram for low-grade material to $50 a gram for nicer goods. “The reason for the low prices is the risk involved in buying new ‘untested’ material,” says Farnsworth. Moreover, he notes, the material is being sold in mixed lots.
Article from the Rapaport Magazine - December 2011. To subscribe click here.