Last week, we received a first batch of six stones back from AGS. Let me tell you how we experience the grading of AGS.

1. The grading system

Where the current cut-grade consists of the following three factors, proportions, polish and symmetry, the new grade will have three different factors:

• Light performance
• Proportion factors
• Finish

1.1. Proportion factors

This factor is on the one hand a very important factor, while on the other hand, it is relatively easy to achieve an Ideal grade. In this factor, certain detrimental effects are observed:

• The girdle thickness is checked in order to make sure that the diamond has neither a too thin nor a too thick girdle.
• The culet size is checked.
• A spread-factor is observed, in order to make sure that a diamond has a surface, which is in line with its weight.
• Durability issues are checked, like a too thin girdle or a too low crown angle.
• Finally, tilt is checked, in order to make sure that the girdle does not reflect under the table, after minimally tilting the diamond.

For a cutter, aiming for AGS-0, obtaining Ideal on this factor is straightforward and easy. For a consumer however, this is a very important factor, since it addresses very important problems like durability and spread.

1.2. Finish

Finish consists of two factors that we already know, polish and symmetry. This grading basically is the same as in the current AGS-system for rounds.

At the end of last year, one could deduct from some AGS-presentations, that the grading for Polish and Symmetry would be loosened to the extent that the current Excellent-grade would be included in an Ideal-grade. Apparently, this idea was abandoned, and there still is a clear distinction between the Ideal and the Excellent grade.

1.3. Light performance

Light performance consists of brightness (or brilliance), fire, scintillation and contrast. AGS has developed a complete software-system, based upon its studies, and they use this software to judge light performance.

In order to help cutters, AGS has distributed 'cutting guidelines', which gives combinations of proportions, that should yield candidates for AGS-0, and for all the other AGS-scores. However, it is very important to understand that 'cutting guidelines' are not 'grading guidelines'.

In grading, the first step is to take a 3D-scan of the diamond. After the accuracy of this scan is checked, it is introduced into the AGS-software. This software performs a series of ray-tracing, and finally returns scores according to the AGS ASET-system. These scores are compared to certain values, and if a diamond scores in the Ideal-range on all these scores, it will be graded Ideal on Light Performance.

Light Performance-grading will make the big difference with the current AGS-system. While, in theory, a cutter has many more possible combinations to cut an AGS-0, each combination needs such total precision that it is very difficult to obtain this.