The Fire Inside
Forget heat treatment—some gems are just naturally 'hot.'
By Gary Roskin, G.G., FGA, Senior Editor -- JCK-Jewelers Circular Keystone, 8/1/2002
Red hot. Fiery orange. Sunshine yellow.
Red, orange, and yellow gems can evoke images of heat and flame. Some even have trade names that fit their fiery natures: flame opal, in which ribbons of red play-of-color race across the surface of the gem; fire opal, with its vivid, saturated reddish-orange hue; and flame spinel, a fiery orangish-red.
Not every red, yellow, and orange gem produces spectacular fiery colors—only a few from certain localities do. Some commercially available gemstones, such as yellow sapphire and orangey-yellow spessartite, may have the right hue, but they don't have the right stuff—they're just not hot. Gem varieties such as citrine (yellowish-orangey quartz) and heliodor (golden or greenish-yellow beryl known as "gem of the sun") also fail the flame test.
Spessartite is one of the gem varieties that differ from one locality to another. The "Little Three" mine in Ramona, Calif., has produced outstanding vivid, saturated orangey specimens, but few are available. Nigerian spessartites are available, but their color, though nice, is generally much less intense and less orange than the color of the California stones.
No disclosure necessary. Paler yellow, orange, and red gems can appear bright and colorful with normal flat faceting, but they're often cut to retain weight and end up looking dull and having "windows" in the pavilion. But the right cutter and the proper cutting tools can help a gem catch fire.
One of the best examples of how cutting can improve color is concave faceting, a technique that's been around for just over a decade. An increasing number of concave faceters are entering the market, and Chinese cutters are learning the technique for mass-market cutting. Concave faceting eliminates "windowing" and concentrates—in fact, intensifies—the color within the gem.
But traditional flat faceting also can be redesigned to reveal more color. One excellent example is the domed checkerboard crown cut, which can enhance overall color and brightness.
For information on concave faceting, see "The Art of Concave Faceting," by Soosai Prosper, The Canadian Gemmologist , Summer 2002, Vol. 23, No. 2. (Prosper, of Byrex Gems in Toronto, Ontario, receives e-mail at sprosper24k@hotmail.com.)
For more information regarding concave faceting, e-mail Richard Homer of Gems by Design, Kent, Ohio, at concavegem@mac.com.
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