The CUT of a diamond is the greatest determinant to the beauty of a diamond. It is also the only element of the 4Cs that is within the control of human effort.
The beauty of a diamond ultimately depends on the reflection or the return of light from the diamond. In the 3 sets of diamonds below, the left and middle groups show inferior cut diamonds with a multitude of differing proportions that allow the leakage of light, resulting in many dull stones. The group on the right displays superior cut diamonds with maximum return of light and brilliance.
WHY THEN AREN’T ALL DIAMONDS CUT TO THIS STANDARD?
Because rough is expensive and a cutter is continuously balancing between yield and the beauty of a stone. Further, every facet is hand cut and accurate cutting is difficult to achieve, time consuming and involves greater wastage of expensive rough.
Beyond just a good cut, the most beautiful diamonds are cut to strictly defined ideal cut proportions. These proportions ensure the maximum return of brilliant light, dispersed light and scintillation from a diamond. A diamond that is cut too deep will produce a dark centre in the stone. A diamond that is cut too shallow will result in a dull hollow appearance.
Symmetry refers to how identical and exact the size and placement of each facet is. Below are some images of perfect and imperfect symmetry examples.
Polish refers to the surface finish of a diamond. Perfection is attained when the surfaces are even and flat, with no polishing lines, graining or burn marks.