AGS Gemological Laboratory Background
Article Copyright © 2009 AllAboutGemstones.com
The American Gem Society was founded in 1934 by Robert M. Shipley, creator of the Gemological Institute of America (GIA), along with a consortium of independent jewelers. The mission of the AGS is to increase consumer awareness, and to set a higher standard of business ethics and professional practices in the jewelry industry. The AGS Gemological Laboratories was established in 1996 to provide state-of-the-art diamond grading and appraisal services to the jewelry industry.
Today, AGS is considered the premier diamond-grading laboratory, having the most rigid grading standards, as well as the most comprehensive system for grading the all-important 'cut' parameters. The AGS specializes in diamond testing and evaluation, and does not evaluate other types of colored gemstones. An AGS report, referred to as a "Diamond Quality Document" or "DQD," is not an appraisal of monetary value, but rather a comprehensive quality evaluation. The AGS Diamond Quality Document uses a unique and proprietary 0 to 10 grading system that is simpler for the consumer to understand than the GIA's grading nomenclature. AGS grades diamond color on a numeric sliding scale that is similar to GIA's alphabetical scale. A diamond's clarity is also graded on a simple numeric scale from 0 to 10, as opposed to GIA's vvs, vs, and s ratings.
Cut Grade: Finish, Proportions & Light Performance
The AGSL was the first gem lab to grade a diamond's cut quality using three parameters: Polish, Symmetry, and Proportions. Each parameter is given a numeric grade from 0 (Ideal) to 10 (Poor). In 2004 AGS added a new category that is referred to as "Light Performance," but to retained the "Triple Zero" monicker for diamonds with a perfect score, 'Polish' and 'Symmetry' were merged into one category called "Finish," and "Proportions" was renamed "Proportion Factors." The AGS Cut grading system was developed through years of research by gemologists, mathematicians, and optical physicists.
AGS uses the "Light Performance" designation to quantify 'light return' by using a ray-tracing software program to follow the path of light rays as they travel through the diamond. The ray-tracing program measures the quantity of the light being returned to the viewer by quantifying brightness, contrast, dispersion, leakage and light spread.
AGS Triple Ideal or 'Triple 0' Grade
The gold-standard for a diamond's AGS cut-grade is the "triple zero," or "ideal" rating. When all three parameters are in perfect harmony the diamond is given a "Triple 0" or "Triple Ideal" grading. The AGSL grades a diamond's symmetry and proportions according to the accuracy of crown/pavilion angles, where facets intersect with each-other, relative facet angles, and individual facet ratios; all measured in three spacial dimensions.
AGS Diamond Grading System
On the inside fold of an AGS Diamond Quality grading report there is a legend explaining the unique AGS nomenclature with comparisons to GIA's grading system, as well as the symbols used to identify inclusion or internal flaw types that are 'mapped' and marked on the 'Proportions' diagram. AGS uses a 3D-scan of the actual diamond, in conjunction with proprietary AGS mapping software (similar to a Sarin or OGI scan) to create the line diagram shown on the report (above).
AGS Diamond Color Saturation Designations
- Colorless - 0 to 1.0 (GIA Equivalent: D to F)
- Near Colorless - 1.5 to 3.0 (GIA Equivalent: G to J)
- Faint - 3.5 to 4.5 (GIA Equivalent: K to M)
- Very Light - 5.0 to 7.0 (GIA Equivalent: N to R)
- Light - 7.5 to Fancy (GIA Equivalent: S to Z)
As of 2003, the 'inert' and/or 'faint' fluorescence designations (lower left corner of document) have been replaced by a single term 'negligible,' meaning "not significant or important enough to be worth considering."
Each AGS grading document is marked with a hologram (dark circle at lower right of report) and watermarking or embossing to prevent fraudulent duplication. In the upper left corner of the document there is a unique AGS reference number that can be used when contacting AGS with questions about your report.
Triple-0 Round Brilliant Setting
'American Star Diamond' 13.42 Carat D, Flawless
Other Services Supplied by AGS
The AGS will soon be entering into an alliance/partnership with one of the premier testing labs of colored gemstones, the American Gem Trade Association (AGTA), through AGS offices in Antwerp, Dubai, India and Israel. The AGS supplies 'facet arrangement' templates corresponding to their cut-grading system, which are used by non-contact measuring-device manufacturers such as Sarin Technologies, OctoNus Software, and OGI Systems. AGS will also provide analysis of a manufacturers 'cut performance' by analyzing a sample stone's Sarin file, so that the cutter can improve the light performance of their cut stones.
Obtaining an AGS Report
AGS is a 'trade-industry' testing laboratory that will only evaluate diamonds sent from jewelers or manufacturers. Additionally, AGS will only evaluate loose, unmounted diamonds. Pricing for a diamond grading report is based on carat weight. As of 2005, AGSL reports will also grade cut quality for emerald, princess, and octagon step-cut diamonds, and will soon be offering cut evaluations for other fancy shapes. AGS offers laser inscription services as well.