A diamond cut is essential to knowing how to buy a diamond. The cut of a diamond is the art of its beauty. It is what makes every angle and facet dazzle when interacting with light.

A well-polished and symmetrical diamond will ensure it uses the light in the most effective way. The diamond will appear brilliant and fiery with superb scintillation.

Diamonds are cut with three optical effects:

• Brilliance:
  • The two fundamental aspects of brilliance are contrast and brightness. Bright diamonds return maximum light, meaning light entering the top of the stone is reflected back to the top by the lower facets. Light that doesn’t return from the lower facets create areas of contrast. A stone that is cut too deep or shallow will have more dark areas.
• Fire:
  • Fire is a measure of the prismatic effect of a diamond and how different colors of light flash in low light conditions. Diamonds with the most fire are those with smaller tables and steep crown angles. Fancy cuts, and “old” cut diamonds often have the most fire.
• Scintillation: ​
  • Scintillation is simply the sparkle of a diamond. It is the balance of black and white under light. Fire can actually add to a diamond’s scintillation under direct light. The best cut for scintillation is one that has many facets across the diamond’s surface.

“A well-cut diamond will have more life and sparkle than one with a lesser cut quality,” the AGS points out. And the way a diamond is cut is graded as well.

Different gemological laboratories use different nomenclature when grading cut. The American Gem Society has developed a diamond cut grading scale that rates from zero to ten, which is useful when understanding how to buy a diamond. Their grading scale examines essential elements associated with a diamond’s cut in order to ensure the proportions will maximize fire and brilliance.

Elements of a diamond cut grade:

• Table Percentage
• Depth Percentage
• Crown Height and Angle
• Pavilion Depth and Angle
• Culet
• Girdle
• Star Length

AGS grading scale:

• 0 – Ideal Cut
• 1 – Excellent Cut
• 2 – Very Good Cut
• 3 and 4 – Good Cut
• 5 to 7 – Fair Cut
• 8 to 10 – Poor Cut

Only round stones are given cut grades on diamond certificates, but all shapes have ideal ranges and values for the elements that impact the cut of the stone.

The cut of a diamond is also associated with its shape, and sometimes the two words are used interchangeably. However, the two are different for professional jewelers. Cut refers to the arrangement of facets, and shape is designated for the diamond’s outline. There are a variety of diamond shapes, all fashioned to accentuate a particular characteristic of the diamond.