Cut

Cut is often confused with the shape of a diamond, but while shape is largely a matter of personal taste and does not itself determine the value of a diamond, the cut does. Most diamonds are cut with a full 58 facets. Only skilled master cutters can give a diamond a "good cut" in such a way that as much light as possible is reflected through the dimaond, thus giving the diamond a more sparkling appearance.

The reflection of light through a diamond.

Cut to the right proportions, a diamond reflects light from ome facet to another. This light is dispersed through the top.
If the cut is too deep, light escapes through the opposite end of the pavilion.
If the cut is too shallow, light escapes through the pavilion before it can be reflected.

The many facets of a round,
brilliant-cut diamond.