Updated: Feb 6, 2022
Here's what you need to know about the cut of a diamond...
Why The Cut Is So Important
Diamonds are renowned for their ability to transmit light and sparkle so intensely!
Cut is often confused with the shape of the diamond. The most common diamond shape used in jewelry is the standard round brilliant. All other diamond shapes are known as fancy shapes. Traditional fancy shapes include the marquise, pear, oval, and emerald, princess cut, cushions, triangles and a variety of others.
The quality of the cut is crucial to the diamond's final beauty and value. Of all the 4Cs, it is the most complex and technically difficult to assess.
If the cut is too shallow: Light is lost out the bottom causing the diamond to lose brilliance
If the cut is too deep: Light escapes out the sides causing the diamond to appear dark and dull
The cut of a diamond determines its brilliance. There is no single measurement of a diamond that defines its cut, but rather a collection of measurements and observations that determine the relationship between a diamond's light performance, dimensions and finish. Most gemologists consider cut the most important diamond characteristic because even if a diamond has perfect color and clarity, a diamond with a poor cut will have dulled brilliance.
The width and depth can have an effect on how light travels within the diamond, and how it exits in the form of brilliance.
The 7 Components of Grading
The Cut Grading System for the standard round brilliant diamond evaluates seven components. The first three, brightness, fire, and scintillation, consider the diamond's overall face-up appearance. The remaining four; weight ratio, durability, polish, and symmetry, assess a diamond's design and craftsmanship.
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 sparkle a diamond produces, and the pattern of tight and dark areas caused by reflections within the diamond
The design and craftsmanship of the diamond considers weight ratio (weight of the diamond relative to its diameter), the diamond's girdle thickness (which affects its durability), the symmetry of its facet arrangement, and the quality of polish on those facets.
Frequently Asked Questions
Q: How does pavilion depth affect a diamond's cut?
A: The distance from the bottom edge 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 from the side of the stone and or leak out of the bottom. A well-cut diamond can let more light return through the crown.
Q: Why doesn't GIA offer a cut grade for fancy-shape diamonds?
A: Establishing quality parameters for fancy-shape diamond cuts is extremely complex-much more so than for round diamonds because of the greater variations in shape and measuring technology needs to progress far enough to capture the features considered important for fancy shapes.
Q: How is diamond cut evaluated for standard round brilliant diamonds?
A: A sophisticated optical measuring devices to capture the measurements of those facets that influence the diamond's face-up appearance. A diamond's cut grade is established by comparing these measurements against a database of more than 38.5 million proportion sets of known grades and by the visual observations of polish and symmetry by diamond grading experts.