AGS vs GIA Diamonds

Arguably the two most important gem labs in the world are the GIA (Gemological Institute of America - Gem Trade Laboratory) and the AGSL (American Gem Society Laboratories). GIA is by far the best known lab in the world with facilities in most of the major trading centers in the world. AGS is small by comparison but extremely important, having made a name for itself as a pioneer in the critical area of diamond cut quality analysis. The discussion of AGS vs GIA reveals more similarities than differences between the two labs, with an AGS certificate shedding light in areas lacking in a GIA report.
Vatche U-113 6-Prong Solitaire Engagement Ring
Vatche U-113 6-Prong Solitaire Engagement Ring
By virtue of having created the diamond grading system that is used in one form or another by all the serious labs in the world, GIA has by far the greatest reach of any lab on the planet. It is held in very high regard and trusted by millions of diamond consumers and businesses worldwide. However, in the area of cut grading GIA was late to the party and continues to lag behind, and that has fueled the demand for the services offered by the AGS Laboratories.
AGSL PGR DLP with Advanced ASET Light Map
AGSL Diamond Certificate
GIA Diamond Certificate
GIA Diamond Certificate
Both organizations were originally founded by the same group of jewelry professionals. The GIA was founded as an institute of research and knowledge for the diamond and gemstone trade, while the AGS was founded as an organization of retail jewelers bound by the highest code of ethics in the industry.
In the mid 1990s the American Gem Society recognized a growing need in the market and established its own gemological laboratory devoted to the understanding of the least well known of the diamond “4 C’s” – Cut grading. Both GIA and AGSL use similar grading standards for color and clarity, and report on the measurements of the diamond in a similar manner. The big difference is in the comprehensive and critical analysis done at the AGSL in terms of cut grading.
AGSL essentially stepped into the void created as more consumers became interested in the quality of cut, and while GIA was not yet providing that information. During the ten years before GIA stepped up to the challenge AGS gained a reputation for doing accurate and consistent diamond grading and enabling a growing number of consumers looking for diamonds with top light performance to easily find them. Today, a rapidly growing number of diamond shoppers are learning about the significant impact of cut quality on diamond beauty. For these astute shoppers an AGSL Platinum certificate is the pedigree of preference.

GIA vs AGS - Color and Clarity grading

As mentioned, AGSL uses essentially the same methodology as GIA for color and clarity grading, and has established practices to maintain consistency with GIA standards. For instance, both labs use master color sets for grading diamond color. The master sets used by the AGSL are graded by GIA and assembled according to the strict standards GIA has established for their use.
Diamond Color Grading Scale from Ags and GIA
Diamond Color Grading Scale (click image to enlarge)
Because color and clarity aspects of diamond quality involve some degree of subjectivity and are ultimately graded by humans, conjecture is often heard that one lab grades more leniently on one or the other aspect than the other lab. The fact is that all major labs recognize an inherent one-grade acceptable deviation between them. There have been and always will be cases where diamonds submitted to both labs result in different grades. And those differences go in both directions. No study has been done to effectively demonstrate that one lab is consistently more or less strict on either color or clarity than the other.
Diamond Clarity Grading Scale
Diamond Clarity Grading Scale

AGS vs GIA – Cut grading on fancy cuts

AGSL has developed the only scientifically vetted system for analyzing cut quality and light performance in diamonds. The beauty of the AGSL system is that it can be applied across multiple diamond shapes and facet arrangements. Today, in addition to rounds, AGSL offers cut quality reporting on princess, oval, Asscher, and several proprietary diamond shapes. Other shapes will eventually be added to the list. In contrast, GIA offers an overall cut assessment only on round brilliant diamonds and has announced no near term plan to roll out cut grading on any other shape.

Lab Certificates and the Rap List

The information about diamond pricing presented in the rap list is only as good as the grading of the diamond in the first place. Second tier labs with questionable grading practices or unreliable accuracy will defeat any meaningful attempts to get a fix on the true value of a diamond. GIA and AGS certificates can be relied upon. Demonstrating the power of a report from AGS Laboratories, Rapaport’s own surveys diamonds show AGS reports actually trade higher than GIA reports on the Rapaport trading network. The graph below was part of a presentation by the founder and CEO Martin Rapaport to the annual gathering of trade members at the JCK convention in Las Vegas. Labs such as HRD and IGI are traded at lower prices than GIA. In 2015 Rapaport banned EGL affiliated labs from the Rapnet Trading Network because of extreme over-grading.
Chart from Martin Rapaport
Chart from Martin Rapaport presentation at JCK Show in 2012

AGS compared to GIA – conclusions

Both labs are highly respected. Both labs perform consistent and dependable grading. For customers interested in obtaining in-depth information related to the cut quality and light performance of their diamond, the AGSL report provides a far better analysis.

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