Gemstone cutters can tilt or 'index' the upper half ( or upper girdle ) facets. This indexing produces different amounts of weight retention from a given piece of rough and produces different optical performance effects. Indexing can also affect crown height and spread ( millimeter footprint versus weight, also called 'weight ratio' ).

Indexing and Optical Performance

Using a 64-tooth gear, a cutter can index the upper halves at 1, 2, or 3.

 All of the stones in this article have a 57 % table, 33.80 degree crown angle, 21.27 degree star angle, 40.80 degree pavilion angle, and 42.02 degree lower half angle. The only difference is the index of the upper halves and the resultant change in angle of the upper halves.

We'll be giving examples with girdle thickness remaining constant at the halves. This is an example:

There will also be examples where the girdle thickness remains constant at the mains. This is an example: