The pavilion angle is the slope of the pavilion mains, measured against the plane of the girdle.
In more detail
It decides how much light the pavilion reflects back up, and it is the most sensitive number on a round. Tolkowsky calculated 40.75° in 1919, and GIA's Excellent limit for the pavilion alone is 40.6° to 41.8°. In our Cut Grading Tool, at a 53% table and a 34.5° crown, Excellent runs only from 40.6° to 41.4°.
On a grading report
On the proportion diagram, in degrees, in 0.2° steps. IGI's Ideal band is 40.0 to 41.3°.
Related terms
- Pavilion depth: Pavilion depth is the depth of the pavilion, from the girdle to the culet. It is a percentage of the average diameter.
- Pavilion main: Pavilion mains are the 8 long facets of a round brilliant's pavilion that run from the girdle to the culet.
- Crown angle: The crown angle is the slope of the bezel facets, measured against the plane of the girdle.
- 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).
- Leakage: Leakage is light that enters a stone and leaves where the viewer cannot see it, mostly through the pavilion. Lower leakage is better.