Published: February 2011
by George Williams, JTV Senior Gemstone Buyer
The exciting arrival of gem quality solid opal from the Welo district of Ethiopia is taking the gem world by storm. Some are confusing the Welo opal, discovered circa 2008, with the original Ethiopian opal discovery in 1994 at Yita Ridge in the Shewa province, which is prone to cracking. Contrarily, once cut, the Welo opals have proven to be as stable as Australian opal or Brazilian opal where only a small percentage may craze or crack.
Australian opals are sedimentary in nature, forming in ancient sea beds, whereas Ethiopian opals originate from volcanic activity. All volcanic opal is called “hydrophane opal." The term hydrophane comes from the Greek words meaning “water-loving” and describes their ability to absorb water and change from opaque or semi-translucent to translucent or transparent. Sometimes this highlights the color play – others will just become transparent or opaque, with no color when hydrated. Hydrophane opals vary widely from source to source, so it is important to learn the characteristics of gems from a particular mine rather than consider all hydrophane opals to be alike in both looks and properties. The good news is that tests by GIA and others have shown that opal from the Welo province in Ethiopia will revert back to its original state, once dried, with no adverse reaction such as cracking.
Stone Group Laboratories of Missouri had similar positive reports on the stability of the current Welo area productions. When many stones were immersed and then left to dry repeatedly (12 times), there was no cracking or change from their original appearance. The laboratory subjected smaller stones to high heat in order to rapidly dehydrate water-soaked stones and found them to be stable even under these conditions. They did further studies on care and handling and strongly recommend that you do not experiment by immersing these opals in water or other liquids or oils, since contamination can occur, leaving residues within the opal. This can eventually change the original body color or the way light is transmitted by the stone, which in turn may affect the color play or brilliance. Immersing hydrophane opal underwater may, in rare cases, cause stress from uneven expansion, which can create a crack similar to those caused by sudden shock. Chances increase if the water temperature is at odds with the stone temperature, if the stone had any previous trauma or if it is set into jewelry. The time period for dehydrating can be minutes to more than a week and will vary depending on stone body type, size and environmental conditions. Do not try and speed up the natural drying process by placing in an oven, under a hot light or hair dryer!
Do not fear accidental situations such as dropping your opal into a wash basin or getting caught in the rain; the absorption is not immediate and requires more time than a quick dip. Like most gems, opal should be handled and cleaned with care. Never use a steamer or ultrasonic, keep away from harsh cleaning agents, perfume, hand soap, high temperatures or sudden temperature changes; simply wipe with a clean soft cloth.
Stress tests are done under laboratory-controlled conditions with distilled water and temperature monitoring. Other tests were made with the knowledge that losses may occur – like soaking in hot tea or immersing after exposing a stone to stress. We commission these types of studies so that we can advise you of all the necessary precautions and possibilities and so you will not take risks with your purchases. These opals are natural- not manufactured- and as such, will vary in their individual properties.
I have bought and sold opals from all sources for a long time and am thrilled with the variety of body colors, patterns, and especially the brilliance of colors that Welo opal displays. Many exhibit brilliance on a scale not seen since the early Andamooka, South Australian productions. Further, beautiful, high-dome cabs are available that best show the beautiful play of color in opal. Welo is as important to the opal business today as the Australian mines were in the previous century. The cornucopia of opal varieties that can imitate Lightning Ridge, Coober Pedy, Andamooka, Mexico or Brazilian opal from this new discovery alone will continue to bring excitement back to this “Queen of Gems” for many years to come.
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