CUT –  A Diamond’s Cut Unleashes Its Light”


Diamonds are renowned for their ability to transmit light and sparkle so intensely. We often think of a diamond’s cut as shape (round, emerald, pear), but a diamond’s cut grade is really about how well a diamond’s facets interact with light. Precise artistry and workmanship are required to fashion a stone so its proportions, symmetry, and polish deliver the magnificent return of light only possible in a diamond. The traditional 58 facets in a round brilliant diamond, each precisely cut and defined, are as small as two millimeters in diameter. But without this precision, a diamond wouldn’t be nearly as beautiful. The allure of a particular diamond depends more on cut than anything else.

GIA’s Definition of Cut:

Refers to how the proportions and finish of a diamond affect its overall appearance and quality. Cut is graded on a scale from Excellent to Poor and incorporates the diamond’s brightness, fire, scintillation, weight ratio, durability, polish, and symmetry. GIA only provides a cut quality grade for standard round brilliant diamonds that fall within the GIA D-to-Z color range.

The Anatomy of a Round Brilliant Cut Diamond:

dia anatomy

To determine the cut grade of a standard round brilliant– the shape that dominates the majority of diamond jewelry– GIA calculates the proportions of those facets that influence the diamond’s face-up appearance. These proportions allow GIA to evaluate how successfully a diamond interacts with light to create desirable visual effects such as:

Brightness: Internal and external white light reflected from a diamond

Fire: The scattering of white light into all the colors of the rainbow

Scintillation: The amount of sparkle a diamond produces, and the pattern of light and dark areas caused by reflections within the diamond

GIA’s diamond cut grade also takes into account the design and craftsmanship of the diamond, including its weight relative to its diameter, its girdle thickness (which affects its durability), the symmetry of its facet arrangement, and the quality of polish on those facets.

In early 2005, GIA unveiled a grading system for standard round brilliant cut diamonds in the D-to-Z color range. This system, the product of  years of intensive research and testing, assigns an overall diamond cut grade ranging from Excellent to Poor.

GIA cut scale

HOW DOES PAVILION DEPTH AFFECT A DIAMOND’S CUT?

If look at a side view of a standard round brilliant the major components, from top to bottom, are the crown, girdle and pavilion. A round brilliant cut diamond has 57 or 58 facets, the 58th being a tiny flat facet at the bottom of the pavilion which is known as the culet. The large, flat facet on the top is the table. The proportions of a diamond refer to the relationships between table size, crown angle and pavilion depth. A wide range of proportion combinations are possible, and these ultimately affect the stone’s interaction with light.

The distance from the bottom of the girdle to the culet is the pavilion depth. A pavilion depth that’s too shallow or too deep will allow light to escape through the sides or the bottom of the stone. A well-cut diamond will direct more light through the crown, making it sparkle.

gia cut guide

Since the appeal of a particular diamond depends more on cut than any of the other 4Cs we are going to devote more than one blog post to it! So please come back next time to continue your diamond CUT education.

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