Grading Colored Gems

Gemstones are the most fascinating natural objects on earth. Ancient historical records show that primitive peoples adorned themselves with gems and believed that gems had magical powers. Some societies even used powered gems for medicinal purposes!

The classification of gems in ancient times was mainly associated with color. In other words, all red stones were once called "ruby," all green stones were called "emerald," and all blue stones were called "sapphire."  Today people wear gems for many different reasons, including fashion, sentiment, and prestige.  As gems became associated with money, the need for accurate identification grew.

The introduction of manmade gems and imitation materials in the 1800's created an urgent need for experts who could separate the genuine from the fake. The invention of the first cultured pearls and green-glass emerald imitations in the early 1900's further created need for gemological expertise. Today virtually all gemstones, including diamonds, have a number of manmade counterparts and imitations.

The 4 C's of Colored Gemstones

Colored stones are graded in a similar way to diamonds. Color, clarity, cut, and carat weight are the main value factors. The difference is that these factors are evaluated and weighted somewhat differently than in diamonds. Diamonds are assigned very precise grades for color, clarity, and cut. In colored stones, color is the main consideration. Unlike with diamonds, a minor clarity difference rarely affects the price of colored stones.

Color: Color in gemstones normally results from the presence of small amounts of trace elements. Some of these coloring agents are an essential part of the gem's composition, while some are introduced as an extra element when the gem is forming in the earth. Regardless, these elements are responsible for the amazing variety of colors we see in the many different gemstones. Even diamonds appear in virtually all colors of the rainbow.  Generally, the more pure and intense the color, the more desirable and more valuable the stone will be.  Once again, a top color is more important than a top clarity.

Clarity: The internal purity or clarity of a colored stone is secondary to the color quality.  Clarity characteristics are often a beautiful part of a colored stone--and a key to identification.  Collectors even value some colored stones for unusual inclusion scenery.  In fact, inclusions can actually increase the desirability and value of certain colored stones.  They do this by creating what is called "phenomena."  An example of highly valued and beautiful phenomena in colored stones is the star appearance in sapphires and rubies, which results from the presence of intersecting "needles" of the mineral rutile.  The cat's eye phenomena in tiger-eye quartz is the result of a similar condition, except the inclusions are lined up in a parallel manner. The value of certain colored stones, however, can be diminished by the presence of inclusions, when those inclusions are so numerous that they interfere with the passage of light through the stone and make it look cloudy.

Cut and shape: Colored stones are cut into a wider variety of shapes and proportions than diamonds are.  Where the round brilliant-cut is most popular for diamonds, other shapes are better suited to show off a colored stone's beauty, such as oval, cushion, pear, marquise, emerald cut, cabochon, mixed-cut, trapezoid, and tablet.  Each cut is chosen to show off the best color and preserve the most weight from a colored stone.  Colored stone proportions also differ radically from those of a well-cut diamond. The bulk of a colored stone may be on the bottom where it has the best chance of returning the most brilliance and best color to the viewer. Certain colored gems look better in some cuts than in other. For instance, the majority of fine quality emeralds are cut in the traditional emerald cut shape.  Opals are always cut with a smooth curved top (en cabochon).  Fine quality rubies and sapphires are normally cut in oval or cushion shapes.

Carat weight: The weight of diamonds and colored stones is expressed in carats. One carat consists of 100 "points" and is equal to 0.200 grams.