GIA Ex vs AGS Ideal Diamonds

Of the diamond “4 C’s”, diamond cut quality is considered by experts to be the most important. Defects in cut quality will result in diminished light performance. And after all, it is brilliance, fire and scintillation that make diamonds beautiful. Thus the debate between GIA Ex and AGS Ideal is one worth exploring.

GIA  and AGSL are the two most important gemological laboratories and both do cut quality analysis on diamonds. The American Gem Society Laboratories began issuing cut grading reports in 1996 setting the standard for Ideal cut, and now grades rounds, princess cuts and several other fancy diamond shapes. The Gemological Institute of America finally began issuing overall cut grades in 2006, but still only grades round brilliant diamonds. There are other very important distinctions between the two labs in how they grade diamond cut quality.

The AGSL is highly specialized in diamond cut quality analysis. They have developed the only scientifically vetted light performance evaluation system for diamonds. Their ASET (Angular Spectrum Evaluation Tool) forms the graphical basis of their system and can be applied to a wide variety of diamond shapes and facet designs. The AGSL performs the most comprehensive and stringent cut quality analysis of any laboratory in the world, and is preferred by consumers worldwide shopping for diamonds with the ultimate light performance.

The GIA is the most well known and trusted laboratory in the world. They literally invented the diamond grading scale for color and clarity that is the basis for diamond trading worldwide. Their reputation for accuracy and consistency is well respected by consumers everywhere. Although there is a scientific component to their cut grading system, it is one that is fairly broad and forgiving.

AGS uses a 0-10 grading scale with 0 representing Ideal. AGS light performance based reports require that a diamond have Ideal light performance, Ideal polish, and Ideal Symmetry in order to receive the coveted grade known in the trade as The Triple Zero®.

GIA uses a 5 grade hierarchy for cut: Excellent, Very Good, Good, Fair and Poor. A GIA report can list overall cut grade as Excellent with either or both polish and symmetry grades being at least Very Good.

It is clear that the AGS system entails more specificity and is more demanding and stringent than GIA cut grading system. And studies have demonstrated that the GIA top grade of Excellent is a much broader category that includes diamonds that would receive AGS grades 1 ,2 and even 3!

The implication for customers comparing a GIA vs AGS diamond depends on their level of interest in ensuring the diamond is of the finest cut quality. If your preference is for light performance and cut craftsmanship to be top notch, a certificate from the AGSL as Ideal will give that certainty. If top cut quality is not required and you just want to be comfortable that the diamond is well cut, then a GIA Ex is sufficient.

For more comparative information please see this article on GIA compared to AGS diamonds. For basic information on laboratory graded diamonds with links to more detailed information please see this article on diamond grading at the AGSL.