Evaluating and Purchasing Opals

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Evaluating opal quality is a specialized business. It is difficult for the average person to tell the difference between a moderately valuable stone suitable for a ring or a pendant and an investment grade black opal worth as much as $20,000 per carat. In addition, the buyer must beware of the relatively recent appearance of "created" or synthetic opals, and of "manufactured" opals that consist of thin layers of true opal material bonded together to make a more substantial gem. some unscrupulous gem sellers have even gone so far as to grind inferior opal material and mix it into a clear epoxy resin, which is then cast into the traditional cabochon shape.

With these caveats in mind, in general, when you see a stone you like, buy it. some factors you can consider in evaluating its quality are the play of color, its "fire," "sparkle" or intensity (brightness), the rarity of the color or colors (pattern), and how "directional" the colors are as it moves.


Intensity The finest gem opals look like someone has turned the color knob all the way to the right. There's nothing subtle about them. They flash and flare and seem to glow with a mysterious inner fire, even in indirect light. One way to spot the most intense stones in a tray of opals is to squint at them and see which ones "pop" out from the rest. (An aside: one of the worst ways to view them is in the harsh halogen lightning of your typical "mall" jewelry store.)

Color Color in opals ranges from the finest milky white to a beguiling azure-green to the rarest and most expensive opal of all, a deep, red-flecked black. Red in any opal is an indication of quality, and therefore greater worth. the iridescent red flecks in most gem-quality opal is also an indication of "fire" or "pinfire," a common measure of an opal's worth.

For those who are interested in a pleasing piece of jewelry rather than investment, color preference is a matter of personal choice. In that light no single color is better than another.

Direction An opal has a definite "direction." The finest opals will show a bright play of color across the entire stone no matter how the stone is viewed. Others may display their colors only when viewed from certain angles. Still others may display their colors from a single viewing angle. In general, the narrower the directional the play of color, the less valuable the opal. The presence of potch - opal that has no play of color, usually white, gray or brownish - on the surface of the opal reduces its value for the same reason, lack of appearance of direction.

Opal Doublets and Triplets If you are on a limited budget, consider an opal doublet, which is an assembled stone with opal on top and another stone, usually obsidian or ironstone, laminated to the back. These are produced to take advantage of high quality opal material that is too thin to stand on its own. Because there is less gem opal involved, they cost a lot less, and the dark background really shows off the play of color in the opal. A high quality doublet will give you the look and beauty of a fine black opal at a fraction of the cost.

Avoid the opal triplet, however. These are assembled out of three materials; the dark background (usually obsidian), a whisper of opal, and a lens-like quartz cap on top. Triplets are cheap, but they tend to look it - and they can fog up when humidity gets between the opal and the quartz cap. Once this happens, they're ruined.

Synthetic Opals Several manufacturers make synthetic opals, including Gilson Opal, Inamori Opal, and others. In general, synthetic opals look too good to be true, with exaggerated fire and iridescence, and a consistency from stone to stone that nature could never duplicate. I have seen tennis bracelets costing upwards of $1,000 made entirely from synthetic opal, and every stone looks exactly like its neighbor. Quite good, in fact, but by their very consistency they betray their synthetic origin. this may be for you, but nature is quite a bit more canny than the most sophisticated laboratory man can devise no two natural opals - unless cut from the same stone - will look the same.

Opal Enhancements Opals can be enhanced by treating them with certain substances and processes. They may be impregnated with plastic or epoxy, surface oiled, soaked in sugar-rich solutions in a sulfuric acid bath to bring out a peppery pinfire effect, or heated in paper or manure to leave a deposit of carbon below the surface. All of these enhancements are temporary, and will not increase the value of the original stone. some of them lead to detrimental effects such as low specific gravity, high porosity, and increased brittleness. Beware anyone who admits to treating stones in these ways, as they are misleading and ultimately damaging to the stone.
   

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Oklahoma City, OK 73132
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