The AGS Diamond Grading Report

The AGS diamond grading report came from AGS Laboratories, the lab arm of the American Gem Society. It used a numeric scale from 0 to 10 for cut, color and clarity, with 0 as the best grade, and it was known for grading cut by measuring light performance. AGS Laboratories stopped grading at the end of 2022, when its research and technology became part of GIA, but many AGS reports remain in circulation.

The American Gem Society and its lab

Robert M. Shipley founded the American Gem Society in 1934 as a trade association for jewelers, three years after he founded GIA. The Society focused on ethics and education for retail jewelers. Its members carried titles such as Certified Gemologist, and it held annual conferences called Conclave.

AGS Laboratories opened in 1996. From the start it emphasized cut grading, at a time when most labs reported proportions but did not grade cut. The AGS "Ideal" cut grade became a well-known label in the trade, especially for round brilliants with precise proportions and optical symmetry.

The 0 to 10 scale

AGS reports translated each grade into a number. Zero was the top of the scale and 10 the bottom. The scale ran parallel to the letter grades used by GIA and most other labs, which are covered in the diamond 4Cs guide.

Color used half steps. D was 0.0, E was 0.5, F was 1.0, G was 1.5, H was 2.0, I was 2.5 and J was 3.0, and lower colors continued up the scale toward 10. Reports showed both the number and the familiar letter, so a stone might read "Color: 1.5 (G)." The diamond color and diamond clarity pages explain what those grades mean.

How AGS graded cut

Early AGS cut grades for round brilliants were based on proportions. A stone had to fall within set ranges for table size, crown angle, pavilion angle and other measurements to earn an Ideal grade, along with Ideal polish and symmetry.

In 2005, AGS introduced a cut grading system based on light performance. Instead of checking proportions against a table, the lab used a computer model of the diamond, built from a 3D scan, and calculated how it handled light. The grade combined several factors:

• Brightness, the amount of light returned to the viewer.
• Dispersion, the potential for fire.
• Contrast, the pattern of light and dark areas that makes facets visible.
• Leakage, light that escapes through the pavilion.
• Weight ratio, whether the stone carries excess weight that adds no beauty.
• Durability, mainly whether the girdle is too thin.
• Polish and symmetry.

The approach let AGS apply cut grades to fancy shapes such as princess, cushion and oval cuts, which have no single ideal set of proportions. That set AGS apart, since GIA's cut grade, introduced in 2006, covers only standard round brilliants.

ASET images

AGS developed the Angular Spectrum Evaluation Tool, known as ASET, to show where a diamond gathers light from. An ASET image is a color-coded view of the stone face-up.

• Red marks areas that return light from high angles, overhead, which tends to be the brightest.
• Green marks areas that return light from lower angles.
• Blue marks areas that reflect the viewer's own head and body, which creates contrast.
• Black or white marks areas where light leaks out.

A strong, even red pattern with balanced green and blue, and little leakage, indicates good light return. AGS light performance reports included ASET maps, and handheld ASET scopes became popular with dealers and enthusiasts for checking stones. The optical properties page explains brightness, fire and contrast in more depth.

Reading an AGS report

AGS issued several report formats over the years, including light performance reports that carried the ASET image and the full cut assessment. A typical AGS report listed:

• Report number, date, shape, measurements and carat weight.
• Cut, color and clarity on the 0 to 10 scale, with letter equivalents.
• Polish, symmetry and fluorescence.
• A proportions diagram and a clarity plot.
• An ASET map on light performance reports.

The guide to diamond certificates covers how to read these sections on any lab's report.

The 2022 move to GIA

In October 2022, the American Gem Society and GIA announced that AGS Laboratories' research staff, intellectual property, technology and Las Vegas facility would become part of GIA. The AGS lab continued grading through the end of 2022 and then wound down its own services.

Starting in January 2023, GIA offered an AGS Ideal report as an add-on to its own diamond reports. It is digital and available for eligible natural and lab-grown diamonds, round and fancy shapes, in the D-to-Z color range. GIA said the combined team would continue light performance research and work toward a cut grade for fancy shapes.

The American Gem Society itself did not close. It continues as a separate trade association for jewelers, with GIA supporting its member education.

How AGS fit among other labs

AGS had a reputation for strict grading and for its focus on cut. Its numeric scale never replaced the letter system, but it influenced how the trade talked about cut quality. The diamond grading labs page compares AGS with GIA, IGI and HRD. The round brilliant cut page covers the proportions that most often earn top cut grades.

Frequently asked questions

What does AGS 000 mean?

It describes a diamond graded 0 for cut, polish and symmetry on the AGS scale, often called "triple zero." It was the top possible cut result on an AGS report.

Is an AGS report as good as a GIA report?

AGS Laboratories had a reputation for consistent, strict grading, especially of cut. Older AGS reports remain valid records, though GIA reports are now more common.

Can I still get an AGS report?

AGS Laboratories stopped grading at the end of 2022. GIA offers an AGS Ideal report as a digital add-on to its own reports for eligible diamonds.

What is ASET?

ASET, the Angular Spectrum Evaluation Tool, is an AGS imaging method that color-codes where a diamond gathers light from and where it leaks light.