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Grading Colored Gems

Learn what to look for. Decide your priorities.
Then make the choice that's right for you.

What Determines the Value of a Colored Gem?
Not surprisingly, color is the single most important determinant of value in colored gemstones. Second most important is the cut of the gemstone, which maximizes the gemstone's life and brilliance. Generally, the more closely a gemstone approximates its pure spectral color, the more desirable it is. And the better the cut, the better the depth of color and liveliness of the gemstone. Clarity and carat weight may also affect value.

Numerous other characteristics contribute to the quality and value of colored gems, including:

Brilliance The intensity of how a gemstone catches light and displays life
Beauty How the gemstone enhances one's appearance (closely related to its color)
Durability The gemstone's ability, when set in jewelry, to withstand normal wear
Rarity The available supply (the harder to find, the higher the cost)
Demand How desirable a gemstone is in the current market
Tradition Using gems for adornment, symbolism or as a means of exchange
Portability In times of turmoil, gems are an investment that can be readily moved

When evaluating a colored gem, ask yourself the following questions:

Is the shade of color attractive?
Does the gemstone have brilliance and life?
Is the color too dark or too light?
Is the gemstone uniformly brilliant, or does it have "flat" areas with no life?
Does the gemstone appeal to me overall?


Color

Color is affected by a number of variables and primarily by the type and intensity of the light. A gemstone's color can appear to change under different lights and environments. A ruby, for example, will not look as red under fluorescent lighting as it will under ordinary incandescent lights or daylight.

Clearly, color is a very subjective matter in terms of what is considered attractive and desirable. Generally, the closer a colored gemstone comes to the pure spectral hue of that color, the better the color and the more valued the gemstone. The spectral colors go from pure red to pure violet. White, black, gray and brown are not spectral colors, but they do affect the tone of a gemstone's color, and, ultimately, the grading. In general, gemstones that are either very light (pale) or very dark sell for less per carat. A rich, deep color is desirable, but not when it approaches black.

Factors commonly used to describe color:

Hue precise spectral color
Intensity brightness or vividness
Tone lightness or darkness
Distribution consistency or evenness of color distribution
Saturation depth and richness of color

A good lapidary (gem cutter) optimizes the proportions of the cut to bring out a gemstone's maximum intensity and color, making it very desirable. A poor cut significantly reduces the gemstone's vividness and depth of color.

 Color may not always be evenly distributed throughout the gemstone but instead exist in zones, layers or spots, giving the appearance of color in areas of the gemstone that are actually colorless. The evenness and complete saturation of color will greatly affect the value of the gem.


Cut

The cut and proportion affect the depth of color and the liveliness projected by the colored gemstone. Unlike diamonds, there is no "ideal cut" for colored gemstones. They are cut to maximize weight recovery and consistency of color from the rough crystal.  The criteria for judging cut quality in colored gemstones also are quite different from diamonds. Oftentimes, the proportions needed to produce the best color in a gemstone would be considered quite poor if that gemstone were a diamond.


Clarity

As with diamonds, clarity refers to a colored gemstone's purity or absence of internal inclusions (tiny spots, fractures or anything trapped within the crystal). While clarity is important, there is less expectation for colored gemstones to be free of natural markings. Depending on the type of gemstone, an absence of inclusions in a colored gemstone can be even more rare than in a diamond and command a higher cost per carat.

The lighter the gemstone, the more visible the inclusions will be. In a darker gemstone, deeper color may mask inclusions, making them matter less. A greater concern for colored gems is the type and placement of inclusions.  A large crack (called a feather) near the surface of a gemstone makes it less durable and disrupts the play of light, detracting from the value. A small, unobtrusive fracture will have minimal effect on the gem's durability, beauty and value. Some natural markings can be desirable to the degree that they validate the origin or variety of the gemstone.


Weight, Size and Density

Excluding coral and pearls, all gems are priced by the carat; typically, the greater the weight, the greater the value per carat (under 50 carats). However, there are a few colored gemstone varieties that become less valuable per carat if they are too large to be mounted. Also, weight and size are not the same thing. Some gemstones weigh more than others because the density (specific gravity) of the basic mineral is heavier. If a diamond weighs 1.00 carats, the same sized ruby or sapphire would weigh approximately 1.20 carats.

Some gemstones are readily available in large sizes. Scarcity of particular sizes among the different colored gemstones will dictate what is considered "large" in the market. Like diamonds, colored gemstones of less than one carat sell for less per carat than gemstones of a full carat or more. Again, what is considered "large" or "rare" differs by gemstone type.

The industry actually measures colored gemstones by dimensions in millimeters in addition to carat weight. Millimeter size of the gemstone often matters more-especially when matching colored gemstones for a ring, earrings, or other types of jewelry.



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