The 4Cs: Cut
Have you ever seen a diamond that really sparkles, shines and seems almost like it's glittering? That is a well-cut diamond.
A well-cut diamond has been cut from rough so that each of it's facets are proportioned exactly right, so that light is bounced from angle to angle and reflected within the stone and back to your eye. This creates the fire, scintillation, and brightness diamonds are known for.
The cut of a diamond includes the symmetry of the stone, how the angles and facets are proportioned to one another, and how well the diamond's surface has been polished so that it reflects the maximum amount of light. These features all combine to give a diamond's cut a grade between poor and excellent.
Round brilliant diamonds are the only shape and cut style that receives a cut grade. This is because round diamonds dominate the industry and are by far the most popular diamond shape. GIA spent decades analyzing each angle of round brilliant diamonds to determine which proportions are considered 'excellent.' While round brilliant diamonds are the only stone given a cut grade, they provide intel on how to judge other shapes based on their proportions (ideal depth, table size, etc).
How well a diamond is cut should be a priority when finding a stone that's right for you. If a diamond has high clarity and color, but is poorly cut, it can look dull and lifeless. A diamond's cut grade is arguably one of the more important 4c's. Sometimes, diamonds are cut to maintain carat weight rather than the sparkle. This is why it's so important to make sure you work with someone you trust to find you a well cut diamond, which are not frequently sold on online platforms.
There are three main cutting styles...
1. Brilliant cut: a combination of kite and triangular facets. This cutting style can be seen in round, radiant, cushion, princess, pear, oval, marquise and heart shapes.
2. Step cut: a combination of rectangular and square facets. This cutting style includes asscher, emerald and baguette shapes.
3. Mixed cut: a combination of step and brilliant cut stones. This includes the princess cut and the cushion cut.
The diamond shape only refers to the outline of the stone -- and diamonds come in many different shapes.