The American Gem Society (AGS) was founded in 1934 by Robert M. Shipley — the same gemologist who founded GIA. While GIA focused on gemological research and education, AGS was created with a mission to protect consumers through ethical standards in the jewelry industry. Today, AGS Laboratories is renowned for having the most advanced and precise diamond cut grading system in the world.
The AGS Ideal Cut Standard
AGS's defining contribution to diamond grading is their performance-based cut grading system. While GIA uses a five-tier system (Excellent through Poor), AGS uses an 11-point numeric scale from 0 to 10, where 0 represents the "AGS Ideal" — the highest possible cut grade.
What makes AGS cut grading special is that it is based on light performance analysis, not just proportions. AGS uses ray-tracing technology to measure how light actually moves through a diamond, evaluating brightness (white light return), fire (spectral dispersion), and contrast (the pattern of light and dark areas). This scientific approach means that an AGS Ideal 0 diamond has been proven to perform at the highest level optically, not just measured against a set of proportion ranges.
The AGS Ideal grade is considered by many experts to be a stricter standard than GIA's Excellent. A diamond that receives AGS Ideal 0 will always receive GIA Excellent, but not every GIA Excellent diamond would qualify for AGS Ideal 0. If cut quality is your absolute top priority, an AGS Ideal diamond is the pinnacle.
AGS Grading Scales
Cut (Light Performance): 0 (AGS Ideal) through 10 (Poor). The overall cut grade is a composite of light performance, proportions, and finish (polish and symmetry). AGS also grades fancy shapes for cut, which GIA does not.
Color: 0.0 (colorless, equivalent to GIA D) through 10.0 (equivalent to GIA M-Z range). While the numeric scale is different from GIA's letter system, the underlying assessments are equivalent and equally strict.
Clarity: 0 (Flawless) through 10 (I3). Again, a numeric scale that maps directly to the standard clarity grades used by GIA.
AGS Report Types
AGS Diamond Quality Document (Platinum): The premium report, featuring the full ASET (Angular Spectrum Evaluation Tool) light map showing exactly how the diamond handles light at different angles. This is the most detailed cut assessment available from any lab.
AGS Diamond Quality Document (Gold and Silver): More concise reports without the full ASET mapping but still including the 0-10 grades for all characteristics.
When to Choose AGS Over GIA
Choose an AGS-certified diamond when cut quality is your highest priority. The AGS system provides more granularity and scientific precision in its cut assessment. AGS is particularly valuable for round brilliant and princess cut diamonds, where their light performance analysis is most developed.
For most buyers, either GIA or AGS certification provides excellent assurance of quality. Both labs are highly consistent, strict, and trustworthy. The choice often comes down to which certificate the specific diamond you like happens to carry.