Cut is considered the most important characteristic of a diamond. A good cut gives a diamond its brilliance, which is the brightness that seems to come from the very center of a diamond. A poor cut will leave even a diamond with perfect color and clarity looking dull. The angles and finish of any diamond are what determine its ability to handle light and, therefore determine its brilliance.
When a diamond is well-cut, light enters through the table and travels to the pavilion where the light bounces from one side to the other before reflecting back out through the table. How the light moves within a diamond is dependent on its cut, and the result of a good cut is the brilliant, flashing, and fiery effect that makes a diamond so attractive.
The width and depth determine how light travels within the diamond, and how it exits in the form of brilliance. If a cut is too shallow, the light seeps out the sides causing the diamond to lose brilliance. If it is too deep, the light escapes out the bottom causing the diamond to appear dark and dull.
Ideal cut: Represents roughly the top 3% of diamond quality based on cut. Reflects nearly all light that enters the diamond. A beautiful and rare cut.
Excellent 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.
Shallow cut: Represents roughly the top 35% of diamond quality based on cut. Still a quality diamond, but will not be as brilliant as a better cut.
Deep cut: A diamond that is too deep and narrow or too shallow and wide. These diamonds loose most of the light out of the sides and the bottom.
Additional Stone Cuts
Master gem cutters, mathematicians, scientists, and jewelers have been developing unique and proprietary cuts to draw the beauty out of gemstone material. Some gem cuts are created to maximize the sparkle, while other gem cuts are created to draw the viewer into the gemstone.