Culet
The small facet or point at the bottom tip of a gemstone's pavilion.
Culet sizes
Grading reports describe the culet from none, meaning a pointed tip, through very small, small and medium up to large. Most modern round brilliants have no culet or a very small one, which is invisible face up.
Old cuts and visible culets
Antique cuts such as old mine and old European cuts often have a large culet. Looking down through the table, you can see it as a small circle or octagon in the centre of the stone. Collectors value this look, and some modern stones reproduce it on purpose.
Culets and settings
A pointed culet is fragile, so settings keep it clear of the metal. In CAD, check that the culet does not touch or pass through the bottom of the head or a gallery rail. It is an easy mistake when stones are positioned by eye.
Rendering
In face-up renders, a large culet shows as a dark or bright spot in the centre of the stone, depending on the environment. If you are rendering a modern stone and see such a spot, check the model, because a flattened tip often means the stone geometry was simplified or clipped. For antique style designs, keep the culet if the real stone has one, since buyers of vintage looks expect to see it.