---
title: "Tolkowsky ideal cut: meaning in gemology"
description: "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°…"
url: https://digitalgemology.com/learn/glossary/tolkowsky-ideal-cut
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · Cuts and shapes

# Tolkowsky ideal cut

Also called Tolkowsky cut, Tolkowsky brilliant, 1919 ideal cut

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](https://digitalgemology.com/learn/glossary/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](https://digitalgemology.com/learn/glossary/pavilion-angle): The pavilion angle is the slope of the pavilion mains, measured against the plane of the girdle.
- [Crown angle](https://digitalgemology.com/learn/glossary/crown-angle): The crown angle is the slope of the bezel facets, measured against the plane of the girdle.
- [Knife-edge girdle](https://digitalgemology.com/learn/glossary/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](https://digitalgemology.com/learn/glossary/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](https://digitalgemology.com/learn/glossary/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).

## Learn more

- [Tolkowsky's 1919 ideal cut: the brilliant that was calculated](https://digitalgemology.com/learn/historic-cuts/tolkowsky-ideal-cut-1919)
- [Crown angle and crown height in a round diamond](https://digitalgemology.com/learn/diamond-anatomy/diamond-crown-angle)
- [Pavilion angle and pavilion depth: how a diamond keeps the light in](https://digitalgemology.com/learn/diamond-anatomy/diamond-pavilion-angle)
- [T57 Round Brilliant Cut](https://digitalgemology.com/cuts/t57-round-brilliant)

[All 328 terms](https://digitalgemology.com/learn/glossary)