Diamond color grading measures how close a white diamond comes to having no color at all. GIA's scale runs from D, which is completely colorless, to Z, which shows a light yellow or brown tint. Each letter represents a small step, and many adjacent grades are impossible to tell apart once a stone is set and viewed face-up.
The D to Z scale
GIA introduced the scale in the early 1950s as part of the diamond 4Cs system. It starts at D on purpose. Before then, sellers used grades such as A, AA and AAA, along with Roman numerals and trade names, and none of these meant the same thing from one seller to the next. Starting fresh at D avoided any link to those older systems.
The letters fall into five groups:
| Grades | Description |
|---|---|
| D, E, F | Colorless |
| G, H, I, J | Near colorless |
| K, L, M | Faint |
| N to R | Very light |
| S to Z | Light |
D, E and F are all colorless, but a grader can still separate them in a side-by-side comparison. Most people cannot see the difference between neighboring grades in the near-colorless range without a reference stone next to them.
How color is graded
Graders judge color face-down. The diamond sits table-down in a white grading tray, and the grader looks through the side of the pavilion. In this position the facets do not scatter light as much, so the body color shows clearly.
The grader compares the stone against a set of master stones of known color under controlled, daylight-equivalent lighting. If the diamond falls between two masters, it takes the lower grade. Labs that grade large numbers of stones also use colorimeters, but trained visual comparison remains the standard.
Why diamonds look yellow
Pure carbon diamond has no color. Most of the faint yellow seen in white diamonds comes from nitrogen atoms that replaced carbon in the crystal as it grew. Nitrogen is the most common impurity in natural diamond, and clusters of nitrogen atoms absorb light at the blue end of the spectrum. Removing blue from white light leaves the eye seeing yellow.
The stronger the absorption, the lower the grade. Diamonds with almost no nitrogen, called Type IIa, can be exceptionally colorless. The diamond chemistry and formation page explains the diamond types in more detail.
Brown tints in the D to Z range come from a different cause, usually distortion of the crystal lattice called plastic deformation. GIA grades brown and gray tints on the same scale, and lower grades may include a description of the hue.
Face-up color and table size
Body color is easiest to see face-down, but people wear diamonds face-up. In the face-up position, a well-cut diamond returns a lot of white light and fire that make faint tint harder to notice. This is why many buyers find G to J stones look white once set.
A few factors change face-up color:
- Cut quality. A bright, well-cut stone masks tint better than a dull, poorly cut one.
- Size. Larger stones show more color because light travels farther through them.
- Shape. Step cuts and shapes with pointed ends, such as pear and marquise, can concentrate color at the tips.
- Setting metal. A near-colorless diamond in yellow gold can look whiter by contrast, while white metal makes tint easier to see.
Table size also has some effect. A larger table can make a stone look slightly brighter and less tinted face-up, though a table that is too large reduces fire.
Fluorescence
Some diamonds glow when exposed to ultraviolet light. Most often the glow is blue, though yellow, white and other colors also occur. Grading reports describe fluorescence intensity as None, Faint, Medium, Strong or Very Strong.
Blue fluorescence and yellow body color are complementary, so in sunlight, which contains UV, medium to strong blue fluorescence can make a faint yellow stone look slightly whiter. A study GIA published in 1997 found that most observers could not tell fluorescent stones from non-fluorescent ones in normal viewing, and that where they noticed a difference, strong blue fluorescence was usually seen as improving face-up color. In a small number of stones, very strong fluorescence can make the diamond look hazy or oily.
The trade has long priced fluorescence as a discount in the colorless grades and as neutral or slightly positive in lower grades. Buyers should judge each stone by eye, since a fluorescent diamond that looks clear can be good value.
Fancy color beyond Z
A diamond with more yellow or brown than a Z master stone moves off the D to Z scale and into the fancy color system. Diamonds of other hues, such as blue, pink, green or red, are graded as fancy colors at any strength.
Fancy colors are graded face-up, using a different set of terms: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Vivid, Fancy Deep and Fancy Dark. The causes of color and the famous fancy stones are covered on the fancy colored diamonds page.
Lab-grown diamonds and color
Lab-grown diamonds are graded on the same color scale. Many CVD stones are grown with little nitrogen and are often processed after growth to remove brown. HPHT-grown stones can be colorless or show color from nitrogen or boron depending on growth conditions.
Choosing a color grade
Many buyers pick a grade that looks white face-up in the setting they want instead of paying for the top of the scale. A common approach is to look in the G to I range for platinum or white gold settings and in the I to K range for yellow or rose gold, then compare stones in person. A well-cut stone in a lower grade often looks better than a poorly cut stone a grade or two higher.
Frequently asked questions
Why does the diamond color scale start at D?
GIA started at D to avoid confusion with older grading systems that used A, AA and AAA, which had no consistent meaning.
Can you see the difference between an F and a G diamond?
Usually not once the stones are set and viewed face-up. A trained grader can separate them side by side, face-down, under controlled light.
Is fluorescence bad in a diamond?
Not usually. Most fluorescent diamonds look the same as non-fluorescent ones, and a few look whiter in daylight. Only rare stones with very strong fluorescence look hazy.
What is the lowest color grade for a white-looking diamond?
It depends on cut, size and setting, but many buyers find stones in the H to J range look white face-up, especially in yellow gold.