The crown angle is the slope of the bezel facets, measured against the plane of the girdle.
In more detail
Tolkowsky calculated 34.5° in 1919. GIA's Excellent limit for the crown angle alone is 31.5° to 36.5°. GIA grades the crown and pavilion as a pair, so a shallower crown can balance a steeper pavilion.
On a grading report
On the proportion diagram, in degrees; GIA reports it to the nearest 0.5°. IGI's Ideal band is 33 to 36°.
Related terms
- Crown height: Crown height is the height of the crown, from the girdle to the table. It is a percentage of the average diameter.
- Bezel facet: Bezel facets are the 8 large four-sided facets on the crown of a round brilliant. They run from the table to the girdle.
- Pavilion angle: The pavilion angle is the slope of the pavilion mains, measured against the plane of the girdle.
- Table size: Table size is the width of the table as a percentage of the average diameter.
- Fire: Fire is the flashes of spectral color that a cut stone sends out. In our census, fire is the share of returned light whose colors leave more than 0.6° apart.