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| Diamonds:Gemology
A Fancy Spectrum
Colored diamonds may be a big part of your future if their availability and growing popularity continue. Learn the basics so you can tell your customer their fascinating story By curious flukes of nature, some very rare diamonds are born the colors
of a rainbow. These are the diamonds for customers who have everything else,
those who covet a jewel Once owned only by royalty, "fancy" diamonds have gone democratic this century, thanks to increased production in Australia, Brazil, Venezuela and parts of Africa where conditions are right for natural color.
Rough and cut diamonds in some of the rarest colors. Their popularity and beauty also have spawned color-induced diamonds and synthetic colored diamonds. These are less expensive, of course, and further expand consumers' horizons in the diamond world. Fancy This
Causes of color – yellow and otherwise – are not as cut and dried as you might think. Infinitesimal impurities, irradiation or anomalies in crystal growth – or combinations of these factors – are the known causes of color. Here's a closer look at each one. Prevalent fancy diamond colors include yellow
and brown. Even some pinks are tinged with brown. Impurities
Two extremely rare red and green rough diamonds. There's a reluctance to cut green rough because the color is often only "skin deep." Natural Ib diamonds, which are related to saturated fancy yellows, are quite rare. Most synthetic fancy yellow diamonds are type Ib also. The color of natural light yellow diamonds can be deepened with irradiation and annealing (heating). Emmanuel Fritsch of Nantes, France, an expert on origin of color in diamonds, says combinations of irradiation and heating "cause color centers which reinforce the originally weak yellow color and, as a result, the treated gem becomes more marketable." Type IIa diamonds contain boron or bits of nitrogen. While they are more often colorless, they also can be pink, blue-green or brown. Type IIb diamonds are very rare and contain boron, which may substitute for some of the carbon atoms. They are most often blue. Crystal Deformity The cause of the color remains a mystery. Some speculate manganese inclusions impart color in thin bands in the crystal lattice. Others theorize it may be a perceived color due to crystal deformation – a missing atom causing a structural defect. It may be a combination of factors. In an added twist, irradiation of type Ib synthetic diamonds has been known to create red. Irradiation Irradiation also causes some diamonds to turn brown or blue to violet. Natural green is very rare. One way to tell the difference is to examine the "skin" of a cut green diamond. Color caused by irradiation is mostly concentrated in stains on the outer layer. Polishing can remove this layer and the color with it. Determination of color origin in green diamonds should be handled by well-qualified gemological laboratory.
– by Robert Weldon, G.G.
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few others can own.
Any diamond that falls between K and Z on the Gemological Institute
of America's color grading scale can contain small amounts of yellow but
not be considered fancy. Any yellow diamond beyond Z is a fancy color and,
as such, commands a premium.
Yellow diamonds are called "canaries" (referring to the yellow
bird) or "cape series" (they were first found in Cape Province
in South Africa). They are type Ia or Ib diamonds, which means they contain
clusters or aggregates of nitrogen atoms. If your store has a spectroscope,
you can see that Ia types show dark lines at the 415 nanometer mark, according
to the GIA Diamond Dictionary. Ia types are quite prevalent in natural
stones of weak, non-fancy yellow color.