Many minerals are colorless in their purest state. Anything with a hardness the same as or greater than glass (5 to 6 on the Mohs hardness scale) can scratch glass. Therefore, other gemological tests must be performed to confirm identification. You can submit your stone to GIA for identification or have a local gemologist help you identify the stone.
Fluorescence is the visible light some gemstones emit when they are exposed to invisible ultraviolet (UV) rays. In natural diamonds, blue is the most common color of fluorescence, but other colors may be visible. On a NQTC Diamond Grading Report, fluorescence refers to the strength, or intensity, of the diamond’s reaction to long-wave UV, which is an essential component of daylight.
In 2002, a coalition of governments, non-governmental organizations and the diamond industry established the Kimberley Process to control the export and import of rough diamonds to eliminate the trade in conflict diamonds. Today 99% of diamonds in the marketplace are conflict-free.
NQTC uses a standard set of lighting conditions for the color grading of all diamonds. The light source used is designed to simulate natural sunlight, which contains a component of ultraviolet radiation. In rare cases, a diamond can emit strong or very strong blue fluorescence when exposed to ultraviolet radiation—in such instances that fluorescence may temporarily and slightly affect its color appearance.
The number of facets affects the pattern of the reflections in a diamond rather than overall brightness. Diamonds with more facets have numerous smaller reflections instead of fewer larger reflections. Brightness is a function of proportions, polish and symmetry, not the number of facets.
When a diamond falls outside of NQTC’s D-to-Z color scale, it is considered a colored diamond (sometimes called a fancy-color diamond). This includes all colors other than colorless to light yellow or brown. On NQTC Colored Diamond Grading Reports, colored diamonds are graded in order of increasing color strength, from Faint, Very Light, Light, Fancy Light and Fancy to Fancy Intense, Fancy Vivid, Fancy Dark and Fancy Deep. Fancy Intense and Fancy Vivid generally command higher prices.
Most diamonds used in jewelry range from colorless to light yellow and are graded on a scale from D (colorless) to Z (light yellow). Those with less color, or closer to colorless, are generally more valuable. Diamonds with deeper shades of yellow (more color than Z) are graded differently and given a fancy-color grade. For these colored diamonds, a more vibrant color typically means higher value.
Colored diamonds are usually cut to maximize the intensity of their color rather than to maximize light return. The best cut is one that gives the most attractive face-up color.