Diamond Cut Education: What You Should Know

One of a diamond’s most beautiful qualities is the way it sparkles in the light - but this distinctive characteristic isn’t a matter of just nature or chance. It’s the result of pinpoint accuracy, years of experience and virtually microscopic measurements. In fact, it takes the use of exact mathematical proportions for expert diamond cutters to shape each stone and maximize light refractions from each of a diamond’s facets.

For example, if the cut is too shallow, the sides of the diamond leak light and the stone loses its brilliance. And if the cut is too deep, the diamond appears dark or dull because the bottom of the stone allows light to escape. A diamond must be cut just right to sparkle, which is why many gemologists consider cut to be the most important of a diamond’s properties. Even perfect color and clarity cannot overcome bad cut!

Diamond Cut and Shape
Although “shape” and “cut” are often used interchangeably, a diamond’s shape is not the same as the diamond’s cut. However, shape does play a role in cut because of the proportion of the facets, and a diamond with unbalanced proportions will be graded poorly.

The shape that most attractively highlights a diamond’s cut is the traditional round shape. Of course, other shapes emphasize a diamond’s different features and your shape selection is best informed by the design you choose as well as your personal preferences. The following chart shows some of the most popular shapes:

To learn more about shape, visit our Diamond Shape Education page here.

Beyond shape and proportions, a diamond’s cut depends upon the combination of two factors: proportions and the qualities of its finish. A well-cut diamond will reflect light evenly, eliminating any dark or dull areas. To ensure a good cut, master diamond cutters evaluate depth and diameter to create optimal proportions. Likewise, diamond graders evaluate length-to-width ratio, outline balance, profile balance, total depth percentage, crown height, pavilion depth, table size, bulge and finish when analyzing a stone.

Diamond Finish
A diamond’s finish incorporates all the qualities the diamond cutter has given the stone. In other words, every feature except the stone’s intrinsic natural formation. To accurately describe each diamond, finish is further divided into two categories: polish and symmetry.

Diamond Polish
A diamond’s polish denotes the overall surface smoothness of the stone’s facets, with a high-quality polish allowing the most desirable light refraction possible and a poor-quality polish creating a dulled or blurred refraction. When diamond cutters polish a stone, they sometimes find slight variations in the hardness or grain. These variances can result in microscopic polish lines, small surface nicks or scratches. Although these imperfections will result in lower grade, they are rarely so severe as to diminish the beauty of a stone to the naked eye.

Diamond Symmetry
A diamond’s symmetry denotes how well the facets align and the overall consistency of each facet’s shape. Poor symmetry can cause light to be misdirected, which, in turn, inhibits optimal refraction. As such, the most common symmetry faults include unaligned facets, facet points that do not meet, round diamonds that are not perfectly round and off-center tables. It is important to note, however, that symmetry grading does not take a stone’s shape or proportions into consideration. In fact, a diamond may have poor proportions and still be rated Very Good symmetrically if the facets are equal and the overall shape is balanced.

Diamond Cut Grading
A diamond’s cut grade evaluates how well it reflects light, with delineations made between Excellent, Ideal, Very Good, Good, Fair and Poor cut grades:

Excellent: The top 1 percentile of diamond cut quality, these diamonds have the highest grades of polish and symmetry and reflect the greatest amount of light.
Ideal: Approximately the top 2 percentile of diamond cut quality, these diamonds reflect almost all the light that enters the stone.
Very Good: Approximately the top 12 percentile of diamond quality, these diamonds reflect almost as much light as the Ideal grade, but are priced lower.
Good: Approximately the top 10 percentile of diamond cut quality, these diamonds reflect most of the light that enters the stone.
Fair: Approximately the top 10 percentile of diamond cut quality, these are still high quality diamonds, but they are not as brilliant as a diamond with a grade of Good.
Poor: Including all other stones, these diamonds are shallow, wide, deep or narrow and they lose most light reflection from the sides or bottom.