The brilliance of a diamond is something truly incredible. The diamond’s ability to intensely transmit light and sparkle comes from how well a diamond’s facets interact with light. And that interaction comes from the cut.
Skilled craftsmen scrutinize each diamond to determine the best cut for a stone that will maximize brilliance through a balance of proportion, symmetry, and polish. Of all the 4Cs, the cut has the greatest effect on a diamond’s beauty and it is one of the first things you visually notice about a diamond besides its size.
While it may seem like a given that diamond cutters would cut a diamond for the most brilliance, fire, and scintillation, other factors are also considered. Depending on the cutter, they may decide to cut to retain as much carat weight as possible. This will leave a diamond too deep or too shallow for optimal light reflection. In another case, the diamond may be cut to minimize the appearance and number of inclusions. This will enhance clarity but diminish sparkle.
The GIA grades diamond cut on a scale of Excellent, Very Good, Good, Fair, and Poor. It is the most complex of the 4Cs to analyze because it is a subjective quality by nature and takes into account many other features of the diamond to conclude an overall grading.
The important thing to remember about this most important component is that cut grading is not absolute. Many of our clients assume that an Excellent cut automatically means it is more brilliant and sparkly than a Very Good cut. The truth is that brilliance is complicated; our eyes not only see light returned, but color, contrast, and sharpness as well.
In showing three diamonds to five people, three to four different answers come back as to which diamond is the prettiest. The idea of cut rating is based on a formula, and this formula is frequently updated based on the latest research. Even the GIA and AGS, both highly respected labs, use a slightly different standard. That means there are some combinations of proportions that receive an Excellent cut at one lab, and Very Good cut at the other.
So the cut grading is a great way to filter out poorly-cut stones. But the best way to choose a diamond is still to see and to compare a narrow list of finalists in person.