Diamond color is caused by the presence of chemical impurities in the earth where they formed, most commonly nitrogen. Color grading for most diamonds is done on a scale of D to Z. A diamond with more color than a Z is a ‘fancy colored diamond’ and could be a different color like blue or pink. Such ‘fancy colors’ are not graded on the normal D-Z scale.
Differing Standards
Many people do not realize that a diamond might receive several different color grades if sent to several different laboratories or appraisers. This is extremely important to consider when considering a purchase: The difference between one or two color grades can be a double-digit percentage up or down in price.
It is most value-conscious to seek out diamonds which were strictly graded. This way you will be paying an “H” price for an “H” color diamond, instead of paying a ”G” or “F” price for that diamond.
Soft Grading
Beware chain stores, malls and discount outlets which use the services of grading labs that use soft standards. These stores will try to sell you (example) an “F” colored diamond that would actually be an “H” if held to strict standards. These soft reports can give casual shoppers a false and negative first impression about warmer colors.
Strict Grading
In the 1930s a gemologist named Robert Shipley established a set of strict international standards. In the USA the grading laboratories using those standards are the Gemological Institute of America (GIA) and American Gem Society Laboratories (AGSL). Diamonds with AGS and GIA reports cost more and hold their value better than diamonds from softer labs.
In Europe and Asia the grading laboratories with similarly strict standards are the Hoge Raad voor Diamant (HRD) and International Gemological Institute (IGI). Their grading strictness is held in similar regard to the GIA and AGSL in the USA.
CUT Influences Color
It’s worthy of noting that diamonds in the D-Z scale are graded face-down, viewed through the pavilion. This is because shape and cut quality both influence how light gets in and out of the diamond. Grading by looking through the pavilion allows a more neutral assessment of body color. Since the brilliant cutting style is most efficient for returning light a round brilliant or princess may show less apparent color face-up than a step cut such as an emerald or an asscher.
Above-Average Cut Quality
Logically, when cut quality is above average, brilliants can “face up” with less color than the grade they were assigned, which was determined face-down. Why? Because light gets in and out faster. This is the opposite of poor cutting (or cutting for colored stones) where the diamond does not have critical angles and light rays escape through the pavilion - or make multiple bounces before leaving - which illuminates body tone. The more superior the cut quality the less color is seen face-up.
Ray-Tracing Example
Light getting in and out of the diamond does not illuminate body color the way light trapped inside the diamond does.
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