The cut is an extremely important factor determining the beauty of a diamond. The cut includes the proportions, polish, and symmetry, and these influence the brilliance, fire, and scintillation of a diamond. It is important for a diamond to have well-cut angles and finish for it to sparkle and allow maximum reflection of light. A poorly cut diamond can appear to be dark, dull, and lifeless. It has the greatest overall influence on a diamond's beauty.

According to IGI standards, a round diamond is graded on its Cut (shape), Polish (surface area), and Symmetry (balance in facets) features separately. For fancy shapes, the Symmetry and Polish Features are graded, Cut is not graded.

When a diamond is fashioned from a rough stone, the cutter must balance optimal cut (to achieve maximum scintillation) against maximum yield (to achieve maximum size and weight as possible). Because many customers are willing to pay more for a larger, fair-cut cut diamond than for a slightly smaller, well-cut diamond, there is pressure on the cutter to sacrifice cut for weight. This is why the Cut grade is so important; it allows the purchaser to identify those stones that were cut Fair to Poor in an effort to gain carat weight.

The Diamond Cut Scale Ranges

• Excellent : Highly reflective and proportionately cut.
• Very Good : Very reflective with well-cut facets.
• Good : Most of the light that passes through is reflected back. The proportions are likely to be less ideal than higher-rated diamonds.
• Fair : Light will start to reflect out of the bottom or sides. These diamonds tend to be small so that their lower shine is not as noticeable.
• Poor : Noticeably dull to the naked eye. These diamonds are less proportionate, resulting in a less reflective stone.