What Is Diamond Cut?

As one of the 4 C's used to describe and determine diamond quality, cut references how well a diamond's facets interact with light. Though it's often confused with shape, which refers to the external outline of a diamond (such as round, oval, or pear), cut is actually responsible for a diamond's ability to transmit light and sparkle. Precise artistry and craftsmanship are required to cut a diamond so that its proportions, symmetry, and polish deliver maximum light return and stunning shine. The better a diamond is cut, the more sparkly it will be.

Why Is Cut Important?

Cut is a crucial factor to consider when selecting a diamond, as it is accountable for its sparkle. An excellently cut diamond will deliver the classic, unmistakable light show you expect from a diamond. A poorly cut diamond, on the other hand, will be much duller. As cut can significantly impact the appearance of a diamond and the light it emits, it's essential to understand what it is and how it's graded.

How Is Diamond Cut Graded?

The Gemological Institute of America (GIA) has extensively studied how light interacts with round brilliant cut diamonds to better understand the factors that contribute to their appearance and sparkle. The result of their studies was the GIA Cut Grading System, which standardizes and evaluates cut quality on appearance (brilliance, fire, scintillation), design (proportion), and craftsmanship (polish, symmetry). Their cut scale ranges from Excellent to Very Good, Good, Fair, and Poor. 

Most independent institutes use their own language to rank the overall cut of a diamond. For example, the International Gemological Institute (IGI) adds an extra rank atop Excellent, rating their highest-quality diamonds as Ideal. At Brilliant Earth, we also use specific scale language to help our customers understand subtle cut differences affecting quality and price. We base our scale on the cut specifications the certifying gemological laboratory provides and rank diamonds from Super Ideal to Ideal, Very Good, Good, Fair, and Poor. This means that, for example, a GIA-certified diamond with an Excellent cut grade will be listed as a Super Ideal or Ideal diamond on the Brilliant Earth site.