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Loose diamonds are color graded against a set of master stones that are already pre-graded. Under the controlled lighting of a GIA Diamond light which is a filtered, cool white, balanced fluorescent light and ideally should be used in a darkened room. The diamonds are turned table down and viewed through the pavilion, color face up may get masked by the brilliance and dispersion of the diamond. The diamond to be graded is moved to the left and right of the pre-graded diamond, to determine the color grade and is often viewed in many different directions. The grading is done against a dull white background using a diamond tray. The three basic components of color grading are hue, tone and saturation.
The GIA color grading system from "D" to "Z"
"GIA's color scale begins with D (colorless) and runs to Z (light yellow). Each letter represents a range of color, rather than one specific color." For example: A color description of G (near colorless) represents a range of color between the finest G and that which is just before H (near colorless). Diamonds that are graded D,E & F are considered colorless, very rare and have a very slight difference in transparency rather than color. The difference is almost indistinguishable in diamonds smaller than 0.25ct. As the size of the diamond increases, the color differences become slightly easier to see. Most diamonds are commonly found with some slight tints of yellow, brown or gray. Diamonds with no body color at all are very rare and extremely valuable. Often people confuse body color with brilliance, dispersion and scintillation seen within the diamond. These three optical effects of light are affected by the cutting proportions selected by the cutter. Brilliance is the internal and external reflections of white light seen primarily through the table, the large octagonal center facet on a diamond. The internal brilliance is caused by the pavilion mains, which act as mirrors reflecting light coming into the diamond and bouncing it back through the top of the stone. This is most responsible for the life of a diamond. The external brilliance is light that is immediately reflected back to the eye that does not enter the diamond. Dispersion or fire is the breaking up of white light into its component spectral hues. The dispersion of a diamond comes mostly from the crown angles. This is where you will see a prism effect, the flashes of spectral colors, many people confuse these colors with body color. Approximately 50% of gem quality diamonds have fluorescence, which allows them to glow when exposed to certain amounts of ultraviolet light. "The glow or fluorescence, results from the interaction between the lights energy and the atoms in the gem." 10% may fluorescent strongly enough to make a noticeable difference in sunlight. The most common fluorescent color in gem diamonds is blue, a strong blue fluorescence in a light yellow diamond can make to diamond appear more colorless in sunlight. So fluorescence can have a positive effect on the diamond, although to strong of a fluorescence can make the stone look cloudy or oily. Most people notice the fluorescence in their diamond, in places where there is less lighting, such as a dark restaurant, a theater or a disco. Fancy colored diamonds are diamonds with a natural bodycolor in any color, other than light yellow, light brown or light gray. "With the exception of rare fancy colors such as blue, pink and red, colorless diamonds command the highest prices." "The GIA GTL Gem Trade Laboratory uses terms such as faint, very light, light, fancy light, fancy intense and dark fancy and the two newest terms of fancy deep and fancy vivid to describe all diamond colors." Many diamonds have some sort of treatment done to enhance the color of the diamond. Most of the treatments include irradiation or a combination of irradiation and heating which would permanently change the color of the diamond. Most treatments are only done to enhance the stones color, and not done to deceive or fool the consumer. The value of a diamond that has been color treated depends on such factors as the original cost of the stone and the expense of treating them. [Cut] [Clarity] [Carat Weight] |
Gemologist examining
the color of a diamond. 
Hue - basic
sensation of color 