The different diamond cuts were developed over the centuries, in order to utilize the most raw diamond and extract the best possible finished diamond. By the turn of the 20th century, mathematical principles were put to use to create theoretical models for developing the ideal models for diamond cuts. It was out of this atmosphere that Marcel Tolkowsky, in 1919, developed the first mathematical guideline for the ideal proportions for a round diamond, in order to achieve the greatest level of brilliance. However, Tolkowsky' s ideal is not the only measure of proportions for diamond cut in use today. The Tolkowsky ideal, or American Standard, is the primary set of proportions in use for measuring an ideal diamond cut in North America. However, each of the other shape of diamond has a guide for the "preferred" proportions and should not be held to the same percentages as ideal rounds.

A diamond is usually cut into one of three basic shapes: brilliant, step and mixed.

Brilliant cut

This is by far the most popular of current cuts. The brilliant cut is characterized by its use of kite-like or triangular facets, angled so as to best create the brilliance and luster of diamond. The round brilliant--with 57 facets (not including the culet), 33 on the crown (above the girdle) and 24 on the pavilion (below the girdle)--and the princess cut are prime examples of the brilliant cut diamond.

Step cut

The step cut is characterized by long, rectangular facets, which run parallel to the girdle, as opposed to the brilliant cut, in which the facets face away, up or down, from the girdle. The emerald cut and Asscher cuts are good examples of the step cut diamonds.

Mixed cut

As the name implies, the mixed cut blends aspects of both the brilliant cut and the step cut. This means that the cut can have both triangular and kite-like facets next to broad, rectangular plane-like facets. This is a cut that is often utilized in colored diamonds, as well as, exclusive trademarked cuts.