Pavilion (gemstone)
The lower part of a faceted gemstone, from the girdle down to the culet.
Pavilion facets and angle
A round brilliant pavilion has 24 facets, plus a culet when there is one. The pavilion angle, measured from the girdle plane, is the most important single measurement for brilliance. In round diamonds, angles close to about 40.6 to 41 degrees tend to return the most light.
Too shallow or too deep
If the pavilion is too shallow, light passes straight through the bottom and the centre of the stone looks glassy, sometimes showing a ring-shaped reflection of the girdle called a fish-eye. If it is too deep, light escapes through the sides and the centre goes dark, an effect called a nailhead. Both make a stone look smaller and duller than its weight suggests.
Pavilions in CAD and renders
The pavilion sits inside the setting, so it is hidden in most images, but it still shapes everything you see through the table. Keep the stone's real depth in your CAD model, and make sure the pavilion does not poke through the back of the setting, which is a common error when a stone is scaled without its seat.
In renders, a correct pavilion only works with the correct IOR. A diamond pavilion rendered with a glass IOR leaks light like a poorly cut stone, so always pair stone geometry with a matching gem material.