The four Cs are color, clarity, cut and carat weight: four scales that describe the quality of a diamond. GIA made them into a grading system in the 1950s.
In more detail
Color goes from D to Z, and clarity has 11 grades from FL to I3. Cut goes from Excellent to Poor, and GIA grades it for standard round brilliants only. One carat is 200 mg. No single C sets the value, but cut changes the look of the whole face.
On a grading report
The grades block of every diamond report: carat weight, color grade, clarity grade and, where given, cut grade.
Related terms
- Carat weight: Carat weight is the weight of a gemstone. One carat is 200 milligrams, a fifth of a gram, and it has 100 points.
- Color grade: 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.
- Clarity grade: The clarity grade says how free a diamond is of inclusions (inside) and blemishes (on the surface) at 10x magnification. GIA's scale has 11 grades in six categories, from Flawless (FL) to Included (I3).
- Cut grade: The cut grade rates how well a diamond's proportions and finish work, from Excellent to Poor. GIA gives it only to standard round brilliants in the D-to-Z color range.
- Diamond grading report: A diamond grading report is an independent lab's record of what a stone is and how it grades. It is true for the day the lab examined the stone.