The standards for grading colored stones are more complex and subjective than those for diamonds. The classic four C's hold true, but they are applied differently for colored stones. In addition, there is a fifth C to consider.
Color The hue, tone, and saturation of a precious gemstone is the most important aesthetic factor in its grading — and in its value. A colored stone that possesses an ideal balance of color and light can be an excellent investment for a collector or anyone who enjoys wearing a truly precious gem.
Clarity The second most important aesthetic factor of the four C's is clarity. In most cases, colored stones that are free of inclusions are more valuable than those with flaws. Stones should be examined for inclusions under 10x magnification, as well with the naked eye. Each species of colored stone has its own limit for the acceptable amount of inclusions. Topaz, for instance, should be clean to the eye, with very few inclusions even under magnification. The standard for emeralds, on the other hand, allows for visible inclusions. Colored stones without inclusions are very rare indeed.<
Cut As with diamonds, cut plays an important role in the grading of colored stones. In the hands of a skilled cutter, an exceptional piece of rough gem material can be transformed into a true wonder. Proper cutting focuses the gem's natural characteristics into a finished work. Poor cutting, on the other hand, can highlight flaws in a stone's character, such as dark or light colored bands within the stone.
Carat Colored stones, like diamonds, are measured in carats. A carat is equal to one-fifth of a gram.
Country of Origin In our complex world, we must consider the origins of every product we buy. With regards to colored gems, many of the world's most coveted stones have their origins in some of the most politically troubled and frequently impoverished nations on the globe. It is a necessity to consider all those involved in procuring any gemstone, from the miners to the cutters, and to seek assurances that they are paid a living wage and are not subject to any abuses in violation of accepted human rights standards. It is also important to make certain that brutal dictatorships and other violent and repressive forces do not benefit from the sale of any gemstone one would consider purchasing.
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