The color grade is a letter from D to Z for the yellow or brown tint of a near-colorless diamond. D is colorless and Z is light yellow or brown.
In more detail
Its 23 letters fall into five ranges: colorless, near colorless, faint, very light and light. GIA started the scale at D to break with the vague A, B and C grades of the past. Labs grade color against master diamonds in standard light, because warm or dim light hides small steps. A diamond with more color than Z leaves the scale and can get a fancy color grade.
On a grading report
In the grades block. An asterisk after the letter means a detected color treatment. IGI also grades D to Z and groups the letters into named bands.
Related terms
- Master stones: Master stones are reference diamonds of known color grade. A grader sets a diamond beside them to decide its D-to-Z letter.
- Colorless (D–F): Colorless is the top range of the D-to-Z scale: the grades D, E and F.
- Near colorless (G–J): Near colorless is the D-to-Z range from G to J.
- Fancy color diamond: A fancy color diamond is a colored diamond with enough color for a fancy grade. To GIA, any diamond outside the D-to-Z scale is a colored diamond.
- Asterisk after the color grade: An asterisk (*) after a GIA color grade means that the lab detected a color treatment. Comments explains what it is.
- Fluorescence: Fluorescence is visible light, almost always blue, that some diamonds give off while ultraviolet light shines on them. It stops when the UV goes off.