An in-depth look into the cut of a diamond

CUT

Diamond cut refers to the quality of a diamond’s facets and their precise arrangement, encompassing critical elements such as proportions, symmetry, and polish. It should not be confused with diamond shape, which only defines the external outline (e.g., round, oval, pear). The cut is key to how the diamond interacts with light, impacting its brilliance, scintillation, and fire. In fact, cut is the most important of the 4 Cs, directly influencing a diamond’s sparkle. Therefore, it’s essential never to compromise on the cut for a truly radiant diamond.

KEY TERMS

Brilliance: The intensity of white light reflected from the diamond's surface and interior. High brilliance makes the diamond appear more vibrant and lively.

Scintillation: The pattern of light and dark areas caused by reflections within the diamond when viewed in motion. Scintillation adds to the dynamic appearance of the diamond.

Fire: The dispersion of light into different colors, seen as rainbow-like flashes within the diamond. Fire enhances the visual appeal of the diamond.

Polish: The quality of the diamond’s surface condition. Good polish allows light to enter and exit the diamond efficiently, enhancing its brilliance.

Symmetry: The precision of the diamond’s facets and their alignment. Excellent symmetry ensures optimal light reflection and refraction.

Finish: The overall quality of the diamond's surface, encompassing both polish and symmetry. A high-quality finish ensures maximum light performance.

ASSESSING CUT

The cut grade reflects how well the diamond has been cut and its ability to reflect light. The GIA categorises diamond cuts into five grades:

Excellent: Diamonds in this category have the most aligned facets and ideal proportions to return the maximum possible light

Very Good: Diamonds in this category reflect most light that enters them, and are very close to excellent cuts in terms of brilliance and fire but may have slight variations in proportions that are barely noticeable to the naked eye. These diamonds offer a high level of quality at a slightly lower price point.

Good: Diamonds in this category reflect a substantial amount of light, but may have more noticeable variations in proportions and facet alignment. They still offer good overall performance and are often chosen for their balance of quality and affordability.

Fair: Diamonds in this category allow more light to escape through the bottom and sides of the stone, resulting in less brilliance and fire. These diamonds may have significant variations in their proportions and symmetry, impacting their overall appearance and value.

Poor: Diamonds in this category exhibit minimal brilliance and fire due to the significant light leakage caused by the noticeable flaws in their proportions, symmetry, and polish, making them the least desirable in terms of visual performance and value. 

THE DIAMOND CUTTING PROCESS

The journey from rough to polished diamond involves several meticulous steps, each essential for achieving a cut that maximizes the diamond's beauty and value. Key factors such as width, table, and depth play crucial roles in determining how light interacts with the diamond, influencing its brilliance, fire, and scintillation. Expert diamond cutters follow specific angles and patterns to enhance the stone’s natural brilliance, ensuring light hits the ideal refraction angle and returns optimally.

  • The planning stage determines how the rough diamond will be cut. Planners examine the rough diamond to understand its internal structure, inclusions, and shape. Advanced tools such as laser mapping and 3D modeling are used to create a detailed map of the diamond, which helps decide the best way to cut the diamond to maximize its yield and quality.

  • Sawing and cleaving are the initial steps in physically dividing the diamond. Cleaving involves splitting the diamond along its natural grain using a precise blow with a steel blade. For more intricate cuts, sawing is employed, often using diamond saws or lasers. Laser sawing allows for high precision, especially useful for complex shapes.

  • In the bruting process, the diamond is shaped into its basic form. This step involves grinding the rough diamond in a lathe to create the basic face-up outline of a round or rounded-shape diamond to prepare it for faceting.

  • Polishing is where the diamond’s true beauty is finally revealed. Initially, the diamond undergoes blocking - where the primary facets are cut. This is followed by brillianteering - where additional facets are added to enhance the diamond’s fire, brilliance, and scintillation. Each facet is then meticulously polished to ensure a smooth surface that optimally reflects light.

  • The final step is inspection, where the diamond is examined under magnification to ensure all facets are correctly placed and polished. Any imperfections are corrected. The diamond may then be sent to a gemological laboratory, such as the GIA, for certification. This provides an official assessment of the diamond’s cut, colour, clarity, and carat weight. 

The diamond cutting process is a delicate balance of art and science. Each step requires expert skill and precision to transform a rough diamond into a beautiful, polished gemstone.