AGS Diamond Ratings
Diamonds have long been rated according to what are known as the "Four Cs": Carat, Colour, Clarity and Cut. Of these the first three are relatively easy to grade using the appropriate equipment - especially carats, which is simply the weight of the stone. However attempting to grade the cut of a diamond is more complex, requiring a degree of human analysis and judgement together with some form of ideal model against which to measure any particular gem.
What Is The AGS Diamond Score?
In the US the generally accepted standard scale for rating round brilliant diamond cuts is that of the American Gem Society (AGS). The AGS system gives each cut diamond a score from 0 to 10 - with zero being the best. These ratings can be summarised as follows:
| AGS Score | Grade Description |
|---|---|
| 0 | AGS Ideal |
| 1 | AGS Excellent |
| 2 | AGS Very Good |
| 3 - 4 | AGS Good |
| 5 - 7 | AGS Fair |
| 8 - 10 | AGS Poor |
Why is 0 the best grade and 10 the worst? The AGS cut score is essentially a "fault" based system. A stone begins with a score of zero and one "black mark" is added for each deviation from the ideal.
The need for a theoretically pefect stone means that it isn't possible to provide a simple score calculator for every diamond. Currently the AGS will rate round brilliant and square princess stones, they plan to extend the system in the future to grade other fancy cut diamonds.