UNLEASHING THE LIGHT
CutAnatomyDiagram

Diamonds are renowned for their ability to transmit light and sparkle so intensely. We often think of a diamond’s cut as shape (round, heart, oval, marquise, pear), but a diamond’s cut grade is really about how well a diamond’s facets interact with light.

Cut quality is the factor that fuels a diamond’s fire, sparkle and brilliance. The allure and beauty of a particular diamond depends more on cut quality than anything else.

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 analyse.

To determine the cut grade of the standard round brilliant diamond – the shape that dominates the majority of diamond jewellery – 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 colours 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.
MAKING THE CUT

The GIA Diamond Cut Grading System for standard round brilliants in the D-to-Z colour range is based on the assessment of seven components. The first three — brightness (the total light reflected from a diamond), fire (the dispersion of light into the colours of the spectrum), and scintillation (the pattern of light and dark areas and the flashes of light, or sparkle, when a diamond is moved) — are appearance-based aspects. The remaining four — weight ratio, durability, polish, and symmetry — are related to a diamond’s design and craftsmanship.

In GIA’s system, each component is assessed individually, taking into account the relative importance of that component in the overall cut quality of the diamond. Each cut grade, based on a relative scale from Excellent to Poor, represents a range of proportion sets and face-up appearances. There are many different proportion sets that produce attractive diamonds.

For example, look at a side view of the standard round brilliant (above). 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 that’s 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. It is important to note that a wide range of proportion combinations are possible, and these ultimately affect the stone’s interaction with light and how attractive the diamond is to the person viewing it.

While it is important to consider many components when assessing the overall cut appearance and quality of round brilliant diamonds, an individual’s preferences also play a role. Because each cut grade represents a wide range of proportion sets, individuals have the freedom to choose which particular appearance they prefer within the grade range.

The diamond industry as well as the public can use cut along with colour, clarity, and carat weight to help them make more informed decisions when assessing and purchasing round brilliant diamonds.

Diamond Cut Grading by GIA

This short video explains the GIA cut scale and how GIA classifies round brilliant cut diamonds with a cut grade ranging from Excellent to Poor by factoring in a range of parameters including the diamond’s proportions, culet size, girdle thickness, polish and symmetry descriptions.

Diamond 4Cs
Colour
Clarity
Cut
Carat