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Gemstone Color
The beautiful color of a gemstone is its most defining characteristic, and many jewelers consider it to be the most important evaluation criterion. The three components of a gemstone's color grade are hue, tone, and saturation. The GIA Color Grade Classification list denotes 324 possible varying combinations of these components. Each gemstone has a specific color range and its best color within that range.
Hue is described as the shade, tint or sensation of a color, with 31 basic hues that can be used to describe virtually all colored gemstones. The most valuable gemstones are those that exhibit a pure color and only "slight" hues of other colors in addition to their primary color.

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Tone represents the depth of color, ranging from colorless to black. Gemstone tone is described as light, medium-light, medium, medium-dark, and dark. The most sought-after and valuable tones are those that fall within the medium-light to medium-dark range

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Saturation is described as the strength or purity of a hue. The GIA Saturation Scale ranks from 1 to 6. For warm colors such as red, orange or yellow, levels 1-3 tend to look brownish, while cool colors such as blue and green tend to look grayish. Level 4 does not show traces of gray or brown, but colors are neither strong nor weak. Level 5 colors are strong and level 6 is for extremely vivid color saturation.

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Generally speaking brownish and grayish colors will have a negative impact on the beauty and value of a colored gemstone
Gemstone Clarity
A major part of the value of any transparent gemstone is its clarity. Because gemstones form under unique circumstances, each individual gemstone is comprised of a combination of trace minerals, which create a unique set of identifying marks or inclusions.
Gemstones have different habits of clarity, and for clarity grading purposes are classified into three types. This classification takes into consideration the qualities of each type of gemstone and groups together gemstones of similar qualities based on how likely they are to be to be included.
Type I:
Stones are usually naturally inclusion-free. Gemstones include aquamarine, topaz and tanzanite.
Type II:
Stones are usually naturally included. Gemstones include sapphire, ruby, garnet, peridot, and amethyst.
Type III:
Stones are almost always naturally included. Gemstones include emerald and tourmaline.
Within the three types, gem clarity is graded similar to diamonds, beginning at VVS and going down to I-3. There is no Flawless grade for colored gemstones.
Very, Very Slightly Included:
Minor inclusions are somewhat easy to see using 10X, but still not visible to the naked eye.
Very Slightly Included:
Noticeable inclusions are easier to see using 10X, and may be slightly visible to the naked eye.
Slightly Included 1:
Large or numerous inclusions are easily seen using 10X, and are noticeable to the naked eye.
Slightly Included 2:
Large or numerous inclusions are easily seen using 10X, and are very noticeable to the naked eye.
Included 1:
Inclusions are very obvious and have a moderate negative effect on the overall appearance or durability of the gemstone.
Included 2:
Inclusions are very obvious and have a severe negative effect on the overall appearance or durability of the gemstone.
Included 3:
Inclusions are very obvious and have a severe negative effect on both the overall appearance and durability of the gemstone.
Gemstone Cut
Cutting standards are far more relaxed for colored gemstones than for diamonds. Gemstones, especially rarer ones, are often cut for size and maximum weight retention from the rough. A good cut showcases the gemstone's color, diminishes its inclusions, and exhibits good overall symmetry and proportion.
Gemstone Carat Weight
The carat weight of a gemstone does not necessarily allow you to accurately envision the size of the gemstone. Because different gemstones have different densities or specific gravity, two gemstones that appear to be the same size may actually have very different weights.
Gemstone Enhancements
Gemstone Enhancements are any treatment or process other than cutting and polishing that improves the appearance, durability, value or availability of a gemstone. A gemstone treatment or enhancement is considered permanent if the effect of the enhancement does not change under normal wear or display. Gemstone treatments or enhancements that is not permanent if they wear off or cause the gemstone's appearance to change over time.
Rubies, emeralds, and sapphires usually undergo treatments to enhance color and fill inclusions. The jewelry industry considers treatment of these three gemstones standard practice. Ideal Brilliance considers some treatments as a permanent enhancement that improves a gemstone's beauty and durability, while other enhancements are temporary in nature or alter the basic composition of the gemstone and are unacceptable.
Oil and Paraffin Gemstone Treatments
Gemstones, like emeralds and rubies, are frequently treated with oils and resins. Time and excessive heat can cause this filler to break down, requiring the gems to be professionally repaired. This is an unacceptable treatment.
Resin and Hardeners
Today we have many sophisticated technologies which can clarity enhance gemstones. We now use clear resins to penetrate the open fissures in the stone. Hardners are often added to solidify these liquids. This step prevents the resin from evaporating, thus making the clarity enhancement more permanent than oiling or paraffin enhancing. One such material used in this process is Opticon. This is a more permanent and acceptable treatment.
Treating emeralds with heat and Opticon, a silicate byproduct, is a permanent and acceptable way of dealing with the fissures that commonly include emeralds. The process is similar to oiling but the Opticon acts as a sealant, preventing any change in the appearance of the gemstone if it is exposed to heat.
Gemstone Heat Treatments
Sapphires and rubies frequently are treated with heat. This process permanently enhances color without changing the stone's structure. Most sapphires and some rubies are heat treated to improve color. This process dissolves trace elements that are already in the stone. This treatment is a permanent enhancement and is accepted in the jewelry trade.
Chemical or Diffusion Gemstone Treatment
On a less frequent basis, gemstones can be treated with cobalt, beryllium or other elements to enhance apparent color. However, this only changes the surface of the stone. A scratch can reveal the lighter hue underneath. This process bonds a foreign chemical onto the gemstone's surface to enhance color. This is not a permanent process and is unacceptable.
Most gemstones available today have been enhanced or treated in some way. Heat treatment is a common enhancement that has been used for centuries. The jewelry industry recognizes heating and hardened resins as acceptable permanent treatments for most gemstones.
You can read an explanation of gemstone enhancements from the American Gem Trade Association for a more detailed understanding of various enhancement practices. |