Below the girdle or setting edge, which is usually not polished, is the base; this contains 24 facets, but 25 if a culet is present. The culet, or collet, is a very small facet at the base of the stone, but in modern cut stones, this is usually absent. The base thus terminates in a sharp point, but older cut stones always have a culet. Its absence eliminates the impression of a black spot at the bottom of the stone. Since the culet is generally protected when the stone is mounted in jewelry, its presence is now considered to be a disadvantage.
There are 8 five-sided facets, 4 of which are called pavilion facets and the others quoins. If no culet is present, these facets will be four-sided. The other 16 split facets are triangular in shape, and consist of 8 cross facets and 8 skill facets (also called bottom half or break facets). All these facets may be described by different names, according to the place of cutting.
The angles between the normals of facets should be 45 °. Between the table and templets, they should be about 40 °, between the culet and pavilion about 40°, between the cross facets and the table about 45 °, between the cross facets in the base and the culet about 45 °, and between the star facets and the table about 26°. Totally reflected light should come through the side facets of the crown, and not through the table. These proportions are very important in order to give the maximum brilliancy from the diamond. A well cut stone must have these definite proportions between its width and height, and the facets must be inclined at these angles. Actually, most London lapidaries make the angle between the bezel facets and the girdle 35 °, and the angle between the girdle and the pavilion facets 42 °.