Diamonds are graded for color only as loose, unmounted stones in the inverted position (table down, pavilion up), and under very specific conditions of lighting and background, and also the distance and angle of the observer in relation to the stone. A color scale has been devised by the Gem Trade Lab. of the Gemological Institute of America (GIA) divided alphabetically from D (the absence of color) to Z (fancy yellow color), and is recognized world-wide. Each letter grade represents a small range of color, and not just a single color. Diamonds are color graded by being compared to a set of master stones.
DEF: (Colorless)
GHI: Near colorless; not distinguishable from colorless when mounted
J: Very, very faint yellow
KLM: Faint yellow. Color distinguishable to the trained eye.
NOPQ: Very light yellow to intense yellow color.
RSTUVWXYZ: Increasingly more intense color, gradually ranging into browns.
Effect of Color on Price
In general, as the amount of yellow in the stone increases, the value of a diamond decreases, that is until the fancy color grades are reached, and then the value goes up again.
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Cut
Regardless of the size or shape of a diamond, the cut will be the ultimate determinant of a diamond’s brilliance and fire. Most round, brilliant-cut or fancy-shaped diamonds have fifty-eight delicately angled flat surfaces, called facets. The placement of each facet is intrinsic to the brilliance and beauty of the stone; if the cut is too deep, light will escape through the opposite side of the pavilion, or bottom, of the diamond before it can be reflected. Similarly, a shallow cut will allow light to pass directly through the pavilion. The cut of a diamond is graded on the basis of how well the diamond handles the light coming into it from above.
