The cut of a diamond determines its brilliance. There is no single measurement of a diamond that defines its cut, but rather a collection of measurements and observations that determine the relationship between a diamond's light performance, dimensions and finish. Most gemologists consider cut the most important diamond characteristic because even if a diamond has perfect color and clarity, a diamond with a poor cut will have dulled brilliance.

The width and depth can have an effect on how light travels within the diamond, and how it exits in the form of brilliance

Too Shallow: Light is lost out the bottom causing the diamond to lose brilliance.

Too Deep: Light escapes out the sides causing the diamond to appear dark and dull.

Diamond measurements are calculated and applied to a cut grading scale that makes it easy to understand how well each reflect light:

• Ideal cut: Represents roughly the top 3% of diamond quality based on cut. Reflects nearly all light that enters the diamond. An exquisite and rare cut.
• Very good cut: Represents roughly the top 15% of diamond quality based on cut. Reflects nearly as much light as the ideal cut, but for a lower price.
• Good cut: Represents roughly the top 25% of diamond quality based on cut. Reflects most light that enters. Much less expensive than a very good cut.
• Fair cut: Represents roughly the top 35% of diamond quality based on cut. Still a quality diamond, but a fair cut will not be as brilliant as a good cut.
• Poor cut: This includes all diamonds that do not meet the performance standards of a fair cut. These diamonds are generally deep and narrow or shallow and wide and tend to lose most of the light out the sides and bottom. E. Frai & co.does not carry diamonds with cut grades of poor.