(From the Four Cs)

Diamond CUT refers to the quality of the job the diamond cutter did, and should not be confused with SHAPE. Diamonds come out of the ground rough before skilled craftsmen cut and polish them, which determines the geometric proportions the diamond will have.

The beauty of a diamond is largely determined by how well it refracts, disperses, and reflects light. Poorly cut stones do not provide as much fire (colored sparkle) and brilliance (white sparkle), and are valued considerably less than diamonds with better cut.

Width and depth make up the largest consideration when rating cut, and are noted as Shallow, Ideal, or Deep.

Deep cut diamonds allow light to escape the sides, and the diamond will look dark and dull. Shallow cut diamonds leak light from the bottom, causing the diamond to lose brilliance.

Other factors influencing cut are the polish and the symmetry of the diamond. Polish is the smoothness of the diamond's facets, and symmetry refers to the alignment of the facets. If either is poor, it can cause light to refract improperly within the stone, losing brilliance and fire.

With all these factors considered, diamonds are finally formally rated for the cut using the following scale:

Ideal Diamonds with an ideal cut represent only a very small percentage of all diamonds. They reflect all light perfectly as it enters the diamond.
Very Good A very good diamond cut is almost as brilliant as an ideal cut, but offered at a lower price.
Good These diamonds reflect most light, and make up about the top quarter of all diamond quality based on cut.
Fair These diamonds make up about one-third of all diamond quality based on cut, and are not quite as brilliant as "good" cut diamonds.
Poor Diamonds rated poor fall below "fair" grade and can lose most of their light out the bottom or sides.