įigures 1 and 2 show the facets of a round brilliant diamond.įigure 1 assumes that the 'thick part of the girdle' is the same thickness at all 16 'thick parts'. 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. However, we (Green et al.) now know that a diamond's appearance is composed of many light paths that reflect considerably more than two times within that diamond. 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.Īnother important point to consider is that Tolkowsky did not follow the path of a ray that was reflected more than twice in the diamond. Although diamonds are highly symmetrical, light can enter a diamond from many directions and many angles. A diamond's panorama is three-dimensional. Just as a two-dimensional slice of a diamond provides incomplete information about the three-dimensional nature of light behavior inside a diamond, this two-dimensional slice also provides incomplete information about light behavior outside the diamond. 2001: īecause every facet has the potential to change a light ray's plane of travel, every facet must be considered in any complete calculation of light paths. Some gem cutters refer to an American brilliant cut or a Scandinavian brilliant cut. While the facet count is standard, the actual proportions (crown height and angle, pavilion depth, etc.) are not universally agreed upon. Many girdles have 32, 64, 80, or 96 facets these facets are not counted in the total. In recent decades, most girdles are faceted. 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. The girdle and culet (if any-not part of Tolkowsky's original design) are cut from the ideal brilliant. The ideal proportions are 100% diameter, 53% table, 43.1% pavilion and 16.2% crown.

The original round brilliant-cut was developed by Marcel Tolkowsky in 1919.

Diamond brilliance