Of the 4Cs, cut is the most important characteristic because it has the greatest influence on a diamond's sparkle. Simply put, the better the cut grade, the more it will sparkle.
Even if a diamond has a perfect clarity and colour grade, if it has a poor cut, it may appear dull.
Gemmologists recommend choosing the highest cut grade within your budget. Very Good or better, if possible.
Light Reflection of Diamonds
A diamond's cut grade is an objective measure of a diamond's light performance, or, what we generally think of as sparkle. When a diamond is cut with the proper proportions, light is returned out of the top of the diamond (which gemmologists refer to as the table). If it is cut too shallow, light leaks out of the bottom; too deep and it escapes out of the side.
This rare cut represents roughly the top 3% of diamond cut quality. It reflects most light that enters the diamond.
Very Good Cut
This cut represents roughly the top 15% of diamond cut quality. It reflects nearly as much light as the ideal cut, but for a lower price.
This cut represents roughly the top 25% of diamond cut quality. It reflects most light that enters, but not as much as a Very Good cut grade.
Represents roughly the top 35% of diamond cut quality. These diamonds tend to appear dull or glassy.