The Tolkowsky ideal cut is the round brilliant that Marcel Tolkowsky calculated in his 1919 book Diamond Design. It has a 40.75° (40° 45′) pavilion, a 34.5° (34° 30′) crown and a 53% table.
In more detail
He worked from diamond's refractive index, 2.417, and its critical angle, 24° 26′. His model was a 2D slice with light from straight above and at most two reflections. Our T57 is his plan with a knife-edge girdle, and our T73 adds 16 girdle facets.
Related terms
- Round brilliant: A round brilliant is a round diamond with the brilliant facet plan. It has 33 crown and 24 pavilion facets: 57 in all, or 58 with a culet.
- Pavilion angle: The pavilion angle is the slope of the pavilion mains, measured against the plane of the girdle.
- Crown angle: The crown angle is the slope of the bezel facets, measured against the plane of the girdle.
- Knife-edge girdle: A knife-edge girdle has no girdle band at all: the crown and the pavilion meet in a sharp line.
- Ideal cut: "Ideal cut" has three meanings: an IGI comment, a GIA supplement grade, or a sales word. At IGI it marks an Excellent round with narrower proportions; at GIA it appears only as "AGS Ideal".
- Critical angle: The critical angle is the angle from a facet's normal beyond which light inside a stone reflects totally. It follows from the refractive index: θc = arcsin(1/n).