Summary: How Different Labs Grade Cut
The GIA and AGS both use a grading systems which takes into account some of the following factors: face up appearance, design, craftsmanship, light performance, proportion and finish.
Each gem laboratory has its own grading system for diamonds, and uses its own nomenclature to rate and describe the attributes and characteristics of a particular stone.
GIA: GIA diamond cut grading system runs from excellent to poor. The GIA five grade system runs: Excellent, Very Good, Good, Fair and Poor. GIA breaks their cut grading system down into three categories of assessment:
- Face up Appearance: This includes Brilliance, Fire and Scintillation, the three appearance-based features of the diamond.
- Design: This includes the weight ratio of the diamond and the diamond's durability.
- Craftsmanship: This examines and rates the polish and symmetry of the diamond.
AGS: AGS began grading cut in 1996 and based their criteria on Tolkowsky's proportions. Their grading system runs from 0 (ideal cut) to 10 for poor. The 3 factors that they rate are:
- Light Performance (which includes looking at the brightness, fire, and light leakage).
- Proportion (which looks at the girdle thickness, the size of the culet, the weight, durability and tilt).
- Finish (which involves examining the symmetry and polish of the diamond).
AGA: AGA was the first laboratory to establish a cut grading system for round brilliant and princess cut diamonds. As with GIA, AGA cut grading system runs from Excellent to Poor.
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