CutOf all the 4 Cs, cut has the greatest effect on a diamond's beauty. Cut should not be confused with "shape." Shape refers to the general outward appearance of the diamond - such as round, princess, radiant, emerald, pear, etc.
The term "cut" refers to the diamond’s proportions - its symmetry and polish.
The proportions are the relationships between table size, diameter, depth, crown angle and pavilion depth. Symmetry and polish refer to the quality of the surface, the symmetrical arrangement and the evenness of all the facets. These mathematic equations affect how light travels within a diamond, and how it exits in the form of brilliance and fire.
When a diamond is cut to exacting proportions - neither too deep, nor too shallow - light will reflect from one mirror-like facet to another, and reappear to your eye.
A diamond can be flawless and colorless, but it will not be as beautiful if it doesn’t dance with light. Good diamond cutting can also disguise lower color and can sometimes override lower clarity, due to dazzling light return.
“Ideal” cutting in round brilliant cut diamonds, refers to a recommended range of "best" proportions. An Ideal cut diamond reflects nearly all the light that enters it. Rare and beautifully brilliant, Ideal cut diamonds represent approximately only the top 3% of all diamonds cut.