The color is the most defining factor when evaluating the colored gems. The more attractive the color, the higher is the value. The highest quality gemstones have a pure color and posses very slight shades of other colors. Tone represents the depth of the color, which can range from colorless to black. The tone of a gemstone is described as “light”, “medium-light”, “medium”, “medium-dark”, and “dark”. Bright, rich and intense colors are valued over those that are too dark or light. Colors that are dulled by tones of black, gray or brown are regarded as less desirable.
The brilliant colors displayed by some specific gemstones are optical effects caused when white light is split into its constituent colors. Some gems exhibit unusual optical effects known as phenomena that rare and beautiful and add immense value to the gems. The Cat’s Eye Effect, the Star Effect and the Color Change Effect are very popular phenomena.
Chatoyancy or the Cat’s Eye Effect is a reflection effect appearing as a single bright band of light across the gemstone's surface. It is generally found in Chrysoberyl, Tourmaline and Tigers Eye.
Asterism or the Star Effect appears as two or more intersecting bands of light across the gem's surface. The phenomenon is commonly found in Ruby, Sapphire and Garnet.
3- Color Change
Color change gems have the capacity to distinctly change their regular color when viewed under two different light sources. The phenomenon commonly in Alexandrite, Sapphire and Color Change Garnet.
Iridescence refers to the rainbow like color effects as seen in some specific gems. It is generally found in Opal, Ammonite and Moonstone.
|Rainbow Moonstone Cabochon|
Aventurescent gems posses colorful play of glittering reflections from small metallic inclusions. The phenomenon is common in Sunstone, Aventurine Quartz and Gold Stone.