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Understanding color
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Determining And Grading Color
Understanding color
Understanding color

Realizing that color is an extremely subjective parameter for evaluation, and that many people don't know how to compare one hue from a slight variation of it makes understanding how color is created all the more important. Generally, the basic color of the gem is it's “ hue ”. There are only a specific number of hues in the light spectrum- blue, violet and indigo on the one hand and yellow, red, orange and green on the other. There are no natural gems with absolute hues that have one single, absolute color. Forming naturally, all these gemstones are influenced by the mineral composites around them and other geological and environmental influences, and are therefore subject to tinting.


This secondary parameter for color evaluation is called “ tone ”. ‘Tone' applies to the undercurrent of color that sits beneath the main hue, making it lighter or darker, clearer or more opaque. This refers to the degrees of brown, gray, white and black that sully the primary hue and tint the stone. Tone is extremely important because it takes the primary hue to a certain direction, increasing its worth or decreasing it a great deal. Tone also determines whether the hue is rich and deep or shallow and watery. Generally rich hues are more desirable, making darker undertones prospectively more expensive. However, if a gem is a clean red hue and the tone is very dark, the gem will look almost black. This is true of all the darker hues- red, blue, violet and indigo. Even some green hues will darken almost to black. Mounted, the gemstone will seem absolutely black and unreflective of light. On the other hand, if a gemstone is cleanly hued, but the tone is too weak; the gemstone will look watery and pale, again decreasing value. So, as you can see, determining final color of a gemstone is not an easy task when considering all the variables that can influence it.


Having examined a gemstone for basic hue and then the undercurrent of its tone, the third thing to examine is “ saturation ” or “ intensity ”. Some gemstones have deep hues and lovely tones, but they are dull and lifeless. They lack intensity, reflecting light poorly and having little or no sparkle. An intensely colored gemstone will be vivid and full of life. The fourth and last parameter for evaluation would be to examine the consistency of the gemstones hue across its surface. This is called “ distribution ” or sometimes “ zoning ”- which means the level of unity within the stone, the even distribution of color, tone and intensity on its surface. Intensity serves to enhance tone and hue, so it is important in that sense, but distribution has no set standards of perfection. There are evenly distributed gemstones that are lovely, and some that are just boring to look at. There are also uneven hued gemstones that are doubly attractive for their distinctive markings and some that are just plain ugly.


As opposed to diamonds, where every blemish diminishes the stone's worth, this last factor is less severe in colored gems. In diamonds there is no real distribution of color, but there is the term ‘ clarity' , and clarity plays a part in colored gems only in the case of very pale, pastel colored gemstones that expose every blemish and may decrease the value of the stone. If the gemstone is darkly colored this will have no impact at all. Blemishes are the flaws on the gemstones surface and inclusions are flaws within the stone. Much more significant than clarity in colored gems is the placement of the inclusions. If a skilled stone-cutter can't utilize the gem as it is because of a deep crevice or some other major flaw [sometimes a fracture will actually reach the surface], then the gem will be practically worthless. So clarity has impact on a gem's worth only in the most extremely flawed conditions. This is not to say that distribution isn't significant- gemstones that have very low, inconsistent distribution of color will necessarily lack vibrancy. But in colored gems, as long as the table surface isn't affected, it won't matter much to the price. Very fine-grade, colored gems that are both deep-hued and without inclusions are so rare that they are barely seen in today's markets. A flawless colored gem will bring a hugely disproportional price per carat weight than a regular-grade gem. If you are contemplating buying such a gemstone - always send it to a lab to be tested. Some gem types are known for their inclusions- emerald, for example. Ruby and alexandrite are also known for inclusions that can be seen with the naked eye.


Sometimes the distribution of color on a gem creates a pattern, alternating in deeper and lighter shades that create ‘stripes' or ‘zones' of color. Some gemstone types are almost always marked in such a way; sapphires, rubies and amethyst all display such markings if you hold them to the light and rotate them carefully between your fingers. Some gems are absolutely clear and have a single strip running through them; some are layered softly with same-hue tints that create the great illusion of impossible depth.


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