Cut is probably the most important of the four c’s and is the only one of the four c’s that is controlled by a human being.
The cut of a diamond refers to the angles and proportions (height, width, depth) of each diamond. As one of the four C’s, cut does not refer to the shape of the diamond: round, princess, radiant, oval, emerald, heart, marquise, pear, cushion, asscher, baguette and trillion. Cut dictates a diamond’s reflective quality. Most diamonds are cut with 58 facets. The different angles and the finish of a diamond determine its ability to reflect light and give it its brilliance and scintillation by allowing the maximum amount of light that enters through its top to be reflected and dispersed back, also through its top, into the viewer’s eye.
When a diamond is cut too shallow or too deep, the light that enters through the top is allowed to leak out through the bottom and does not reflect back, making the diamond look less brilliant and firry.
A poorly cut diamond is significantly cheaper than a well proportioned one. Many cutters choose to sacrifice some of the diamond’s beauty to achieve a stone that is a larger carat weight. Some jewelers will downplay a diamond’s bad cut and try to convince you that the diamond is larger. But keep in mind that just because two diamonds have the same weight, does not mean they are the same size.
The cut of a diamond can also affect its durability as well as its beauty. Some cutting faults can make a diamond prone to breakage when it is set or mounted on an engagement ring.
Choosing a diamond’s cut quality is difficult for a lay person. That is why you should always get a certification from GIA, or any of the respected labs, to verify a diamond’s quality.
A diamond’s certificate will list the important proportions of that diamond:
Table percentage (table / diamond width)
Depth percentage (depth / diamond width)
Cut quality is difficult for a lay person. That is why you should always get a certification from GIA, or any of the other respected labs, to verify a diamond’s quality.
Just compare these numbers against a master chart of percentages for that diamond’s shape. A master chart will tell you what the ideal proportions are for particular diamond shape.
The certificate will also list the polish and symmetry of a diamond.
Polish will indicate any nicks, scratches or other flaws on the surface of the diamond.
Symmetry will indicate the accuracy of the cut to the shape and pattern of the facets.
The GIA rates both as EX (excellent), VG (very good), G (good), F (fair) or P (poor). The AGS rates both as ID (ideal), EX (excellent), VG (very good), G (good), F (fair) or P (poor).
A diamond graded very good is your best choice for quality and value. But if you are on a tight budget go for a good rated diamond.