DIAMOND CUTThe round brillant cut is used for diamonds or stones cute like round diamonds.
You may have heard of a term called "Ideal Cut". This term refers to the attempt to cut a diamond into the best proportions to achieve maximum brilliance. The following is a breakdown of what is considered "Ideal Cut" in round brilliants according to "American Ideal / Tolkowsky" and the "European Ideal Cut" (Proportions are given relative to the girdle diameter)
| American ideal - Tolkowsky | European ideal | |
| Total depth | 58.7 to 62.3% | 60.0 to 61.1% |
| Table diameter | 53.0% to 58.0% | 57.5% |
| Girdle thickness | Medium to slightly thick | Very thin to medium |
| Culet size | None to medium | None to medium |
| Crown angles | 34.3° to 34.7° | 34.5° |
| Pabillon depth | 43.1% | 43.1% |
| Finish | Very good to excellent | Good to excellent |
| Crown height | 16.2% | 16.2% |
There are 58 facets in a Round Brilliant Cut including the culet. On the Crown or upper part of the Diamond, these consist of 1 table facet, 8 bezel facets, 8 star facets, and 16 upper girdle facets for a total of 33. On the pavilion, or bottom part of the diamond, there are 16 lower girdle facets, 8 pavilion main facets and 1 culet.
It is this informations that you will find on the laboratory certificates.
If these proportions are not respected, the light entering the table will refract on the cylinder head and come out completely by the table. But also, part of the light will not come out through the table and the stone will lack lights.
The angles given in this table are diamond-specific. For other precious stones and gemstones, th angles are functions of the refractive index proper to each stone variety.
