How to select Diamond Cut

By Robert Underhill


Diamond Cut Grading

The grading of cut should not be confused with the different shapes and cuts of diamonds. For each diamond shape there is a set of proportions critical angles that a diamond should be cut too, in order to maximize its brilliance, fire, and scintillation. The closer the diamond is cut to these standards, the more brilliant it will be.

Unfortunately, cut is the most difficult aspect of diamond grading for a layperson to understand, yet it may play the greatest role in how bright your diamond is. Diamonds that are cut poorly may look pretty good in jewelry stores under high power halogen lights, but they may appear sleepy after they are exposed to poor lighting, makeup, lotion, and soap films.

A properly cut diamond is a bit like a mirror. The reflective coating on the back of a mirror returns light, so we are not able to see through the mirror. The critical angles of an ideal cut diamond combined with its highly refractive properties reflect in the same way.

In contrast, envision a glass removed from a dishwasher with water spots. Since there are no reflective properties, we see through the glass and the water spots are obvious.

Your diamond should be like the mirror. A properly cut diamond will reduce the effects of makeup, lotion and hairspray on the back of the stone.

This illustration represents 3 round diamonds each having the same mass. We will refer to them each as 1 carat in weight.




Diamond 1: The first diamond appears larger than the others from the top view because it was cut wider and shallow. Your first impression might be that that is a good because it looks larger. It is actually very detrimental to the appearance of the stone. This diamond is like the glass in the dish washer. The diamond will be less brilliant and unattractive when it is dirty.

So, why would someone choose to cut a stone this way? The original rough diamond may have been shallow in shape or perhaps part of the rough was heavily flawed and the cutter chose to trim around it.


Diamond 2: The second diamond looks smaller than the others from the top view because it was cut narrower and deeper. Here again, the diamond lacks the brilliance of an ideal cut diamond and it appears smaller than the other 1 carat stones.

So why would someone choose to cut a stone this way? A rough diamond is usually a crystal octahedron and somewhat cube-shaped. The cube that would create a 3/4 carat faceted diamond can be cut deep and chubby to yield a diamond that is 1 carat in weight. An uneducated diamond buyer looking for a 1 carat diamond may believe he is getting a great deal. After all, the rough that this stone was cut from would have normally generated a 3/4 carat stone so it will be priced significantly less than the fine 1 carat diamonds in the market.


Diamond 3: The third stone is ideal cut. The ideal cut stone is faceted at angles that are calculated to return the maximum amount of light to the viewer. Stones in this class are visibly brighter than deep or shallow stones and are the bench mark for quality in diamonds. So why would anyone cut it differently? One reason is that it takes a skilled diamond cutter to position 58 facets in exactly the right position. As with all vocations, there are varying degrees of skill from one cutter to the next. Another reason would be to cut the stone deeper or shallowly, to optimize the profit by increasing its weight or cutting around the undesirable characteristics in the rough.

To summarize: Cut has everything to do with how brilliant your diamond appears. It is for this reason that you should not compromise on the cut grade of your stone. It is not necessary to get an ideal cut diamond however; the cut of your stone should be very good in its rating in order for your stone to be bright and beautiful.