Because most people know little about buying diamonds, the American Gem Society came into existence - now over 70 years ago. Society members developed the precise standards still in use by the AGS for evaluating diamonds.
The 4 Cs, as they are commonly known, are: Cut, Color, Clarity, and Carat Weight.
According to the American Gem Society, Diamond Grading Standards should evaluate three of the four value factors — cut, color, and clarity — on its own 1–10 scale.
By the AGS standards, each of the scales begins at 0 (zero) for the highest grade, and goes down to 10, the lowest.
Each of those three factors is expressed separately, along with the carat weight of the stone - the fourth factor. These standards are represented on certificates issued by the AGS.