The Four Cs: Cut Grading

The Gemological Institute of America (GIA) created the first, and now globally accepted standard for describing diamonds: Color, Clarity, Cut, and Carat Weight.

The creation of the Four Cs meant two very important things: diamond quality could be communicated in a universal language, and diamond customers could now know exactly what they were about to purchase.

In this article we take a comprehensive look at Cut Grading. If you prefer a more condensed version please check out our: “Four Cs: An Overview” article.

In this article we take a comprehensive look at Cut Grading. One of the 4Cs that determine a diamond's value.

proportions & polish deliver the return of light only possible in a diamond.

A diamond’s cut is what unleashes its light, and is oftentimes 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 marquise, pear, oval, and rectangular. Triangles and a variety of other shapes are also gaining popularity in diamond jewelry.

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.

Diamond shape is often confused with Cut, but they are both very different

Diamond shape is often confused with Cut, but they are both very different

Because there are so many variables and options to consider when cutting a diamond, the diamond cutter’s choices (whether man or machine) can produce two otherwise identical diamonds with vastly different levels of beauty, quality and value. This is particularly true of the standard round brilliant cut diamond.

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.

A diamond’s cut is crucial to the stone’s final beauty and value. And of all the diamond 4Cs, it is the most complex and technically difficult to analyze.

After years of scientific research and real-life observation, GIA researchers proved that while every individual facet matters, a diamond’s appearance arises from the combined contribution of all its proportions.

Therefore, for round brilliant diamonds, GIA considers how a diamond’s proportions relate to each other, rather than considering individual proportions in isolation.

To determine the cut grading of the standard round brilliant diamond – 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.

A pavilion depth that's too shallow or too deep will cause the light to leak!

A pavilion depth that’s too shallow or too deep will cause the light to leak!

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 will direct more light through the crown.

GIA uses 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 GIA expert graders.

The GIA Diamond Cut Scale for standard round brilliant diamonds in the D-to-Z diamond color range contains 5 grades ranging from Excellent to Poor. (Excellent, Very Good, Good, Fair, Poor).

Keep in mind that two diamonds of equal cut-grade can have very different values (and prices) depending on three other factors within the 4Cs: Clarity, Color, and Carat-weight.

We hope you found this article helpful in getting an overall sense of  how Cut affects and determines the value and cost of a diamond. However, should you have any additional questions about this or any other jewellery related topics, you can always: “Ask Our Jeweller”

Source: The Gemological Institute of America

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If you’re hungry for even more information on Cut grading be sure to check out our video-post! (it was produced by The Gemological Institute of America)

You may also enjoy this “interactive application on The Four Cs.

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