Since the IGI was establishment in 1975, their grading reports have included a Proportion Grade. The highest Proportion Grade initially started with Very Good followed by Good, Fair and Poor. In 1995, IGI introduced Excellent as the highest cut grade. In 1996, the IGI created the Hearts & Arrows Diamond Report becoming one of the first laboratories to provide an optical symmetry rating.
The IGI believes cut grades should be transparent (all the rules are explained) and, most importantly, user-friendly. The reason is two-fold: 1) if it is not transparent, the trade (including retailers) will not truly understand the Cut Grade parameters, especially at the extremes or borderlines. 2) One cannot expect the consumer to understand a system if the trade (especially retailers) is not in a position to correctly explain the message.
IGI Cut Grade Parameters
| Lab | International Gemological Institute (I.G.I.) | ||||
| Cut > | Ideal | Excellent | Very Good | ||
| Table width % | 53 - 60 | 52.5 - 63.5 | 51.4 - 63.5 | ||
| Crown Height % | |||||
| Crown Angle % | 33 - 36 | 32.7 -36.3 | 31.7 - 36.8 | ||
| Pavilion Depth % | 42 - 44 | 41.8 - 44.3 | 41.5 - 44.8 | ||
| Pavilion Angle | |||||
| Girdle Thickness | Thin to Sl. Thick |
Thin to Sl. Thick |
Thin to Very Thick |
||
| Total Depth% | 58.5 - 62.5 | 56 - 63 | 53.5 - 63 | ||
| Culet size % | |||||