AGS Laboratories Report
AGS Laboratories Report
The grading certificate that defined the Ideal-cut standard for diamonds
An AGS Laboratories report (also known as an AGS certificate) was a grading document issued by the American Gem Society Laboratories (AGSL), founded in 1996 and operating until its acquisition by the Gemological Institute of America (GIA) in 2022. The report is principally distinguished by its proprietary, light-performance-based cut-grading system — widely regarded as the most scientifically rigorous cut-evaluation methodology applied to diamonds in commercial gemmological practice. Although new AGS reports are no longer issued, existing certificates retain their validity as trade references, and the AGS Ideal designation continues to carry meaningful weight in the diamond market.
The 0–10 Grading Scale
Where GIA and most other major laboratories employ descriptive terminology (Excellent, Very Good, Good, and so on) for cut, polish, and symmetry, AGS Laboratories used an inverted numerical scale running from 0 to 10, in which 0 represents the highest grade — designated Ideal — and 10 the lowest. This counterintuitive inversion was intentional: the scale was conceived as a penalty system, with each increment representing a measurable departure from optimal light performance. The grades were expressed as integers, and a stone achieving 0 across all three parameters — cut, polish, and symmetry — was designated AGS Triple Ideal or AGS 000, a benchmark that became a recognised marketing and quality standard within the trade.
The full scale ran: 0 (Ideal), 1 (Excellent), 2 (Very Good), 3–4 (Good), 5–7 (Fair), and 8–10 (Poor). In practice, the commercially significant grades clustered at the top of the scale, with the distinction between Ideal and Excellent carrying the greatest market consequence.
Light-Performance Methodology
The defining innovation of the AGS cut-grading system was its grounding in optical modelling rather than purely geometric proportion analysis. Early cut-grading systems, including GIA's original approach, assessed cut quality primarily by measuring angles and proportions — table percentage, crown angle, pavilion angle, and similar parameters — against empirically derived ranges. AGS Laboratories, working in collaboration with researchers including Bruce Harding and, later, the team that developed the Angular Spectrum Evaluation Tool (ASET), shifted the evaluation criterion to actual light behaviour within the stone.
The ASET is a simple optical device — a reflector map tool — that, when used in conjunction with a corresponding software model, categorises the light entering and returning through a diamond's crown into zones corresponding to brightness (light from high angles), fire (light from low angles), and leakage (light lost through the pavilion). ASET images were incorporated into AGS reports in later years, providing a visual, reproducible record of a stone's light performance that complemented the numerical grade. This approach allowed AGS to evaluate not only round brilliants but also fancy shapes, for which proportion-based grading is considerably less reliable.
Report Contents
A standard AGS Laboratories diamond grading report included the following elements:
- Diamond identification data: shape, measurements, carat weight.
- Cut grade (0–10), polish grade (0–10), and symmetry grade (0–10), collectively expressed as the AGS Light Performance grade in later report versions.
- Colour grade, expressed on the standard D-to-Z scale.
- Clarity grade, using standard GIA-aligned terminology (Flawless through I3).
- A detailed proportion diagram with annotated measurements.
- Fluorescence assessment.
- In later-generation reports: an ASET image and, for some stones, an Ideal Scope or hearts-and-arrows notation.
The proportion diagram was notably detailed by the standards of the era, providing crown angle, pavilion angle, table percentage, depth percentage, culet size, and girdle thickness — information that allowed independent verification of the cut grade by knowledgeable buyers.
Market Recognition and the AGS Ideal Standard
Within the segment of the diamond trade focused on cut quality — particularly among independent jewellers, online diamond retailers, and cut-conscious consumers — the AGS Ideal designation acquired a status comparable to GIA Excellent. Certain retailers built their entire inventory proposition around AGS 0 or Triple Ideal stones, and the designation was frequently cited in consumer education resources as a reliable proxy for exceptional optical performance. The AGS cut-grading system also influenced the broader industry: GIA's introduction of its own cut grade for round brilliant diamonds in 2005 drew on research methodologies that overlapped substantially with the light-performance work conducted at AGSL.
Acquisition by GIA and Current Status
In 2022, GIA announced the acquisition of AGS Laboratories. Following the transition, AGSL ceased issuing new grading reports. Diamonds previously graded by AGSL retain their certificates as valid documentation; the reports do not expire and continue to be accepted by dealers, auction houses, and insurers as legitimate grading references. However, stones requiring new or updated certification must now be submitted to GIA or another active laboratory. The long-term fate of the AGS cut-grading methodology within GIA's own systems has not been publicly resolved as of the time of writing, though GIA has indicated interest in advancing light-performance research.