Brilliant (diamond cut)

A brilliant is a diamond or other gemstone cut in a particular form with 57-58 facets so as to have exceptional brilliance.

The underside is conical, a shape that provides maximal light return through the top of the diamond.

The girdle and culet (if any—not part of Tolkowsky's original design) are cut from the ideal brilliant.

The modern round brilliant consists of 58 facets (or 57 if the culet is excluded), ordinarily today cut in two pyramids placed base to base: 33 on the crown (the top half above the middle or girdle of the stone), truncated comparatively near its base by the table, and 25 on the pavilion (the lower half below the girdle), which has only the apex cut off to form the culet, around which 8 extra facets are sometimes added.

While the facet count is standard, the actual proportions (crown height and angle, pavilion depth, etc.)

This factor further highlights the need to reevaluate Tolkowsky's results, and to recalculate the effects of a diamond's proportions on its appearance aspects.

Another important point to consider is that Tolkowsky did not follow the path of a ray that was reflected more than twice in the diamond.

Once again, we can see that Tolkowsky's predictions are helpful in explaining optimal diamond performance, but they are incomplete by today's [2001] technological standards.

The 2005 AGS cut standards are based on a distance of 25 centimeters (about 10 inches).

Although the hearts and arrows property is indicative of a top-tier cut, it does not always mean the diamond will be the most brilliant.