Color in diamonds is caused by trace chemicals occurring in the earth where the rough crystals formed over millions of years.
D-Z Color Range
Most diamonds are graded using the GIA developed D-Z color grading scale where D is at the top, Z is notably yellow or brownish, and the letters in-between descend very gradually. DEF are considered colorless and GHIJ are considered near-colorless. The colorless and near-colorless ranges are the most popular among diamond buyers as the differences are extremely subtle. Below J, diamonds show progressive levels of “warmth” seen as a yellow or brownish tint.
Fancy Colored Diamonds
A small percentage of diamonds with more color saturation than Z are called “Fancy Colored Diamonds,” or FCDs. Yellow or brown FCDs run from light to vivid. Additionally, FCDs may be an altogether different color like pink or blue. All Fancy Colored Diamonds are graded using a different scale and approach than diamonds in the normal D-Z range.
Diamonds in the normal D-Z range are graded face-down, viewed through the side of the pavilion. This is because shape and cut quality both influence how light gets in and out of the diamond. Grading face-down allows for a neutral assessment of body color. The descending grades from D to Z are very gradual.
The result of face-down grading is the fact that several diamonds of same-grade can appear different colors when viewed face-up. This can be influenced by several factors, including the following:
Laboratory Standards: Different laboratories have slightly different standards for color. Please see the page on Grading Laboratories for more information.
Shape: Brilliant cutting styles return light to the viewer more efficiently than step cuts, so a round brilliant may show less apparent colour face-up than an emerald or Asscher of the same grade.
Fluorescence: A diamond in the near-colorless or faint yellow range may have it’s face-up colour reduced by medium or stronger blue-fluorescence. This is only seen on a case-by-case basis.
Cut-Quality: A diamond cut with the critical angles and precision needed for highest performance have shorter ray-paths reducing their face-up colour; in some cases by multiple grades.
Color and cutting are related.
The finest cut round brilliants often face up with less color than the laboratory colour grade they were assigned, which was determined face-down. Why? Because light gets in and out of the diamond faster, on shorter ray-paths. This is the opposite with poor cutting, where critical angles are missed and light rays either escape through the pavilion or make multiple bounces before leaving, illuminating body tone. Poorly cut stones can face up noticeably darker.
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