How to cut Diamond?

Illustration of diamond cut.

The cut of a diamond influences the way it reflects light, which in turn determines its brilliance. Even a diamond with perfect color and clarity may appear lifeless if it does not have a good cut.

In a well-cut diamond, light enters the stone and is reflected around the mirror-like facets before exiting through the top, or table. This careful orchestration of the movement of light inside the stone and back to the eye is what causes the fiery sparkle we recognize as brilliance.

A skilled professional can maximize this effect by cutting a diamond to very precise proportions. Too shallow a cut will allow light to escape through the bottom of the stone, causing it to look dull. Too deep a cut will cause light to be lost through the diamond's sides, making it appear dark.

Depth is not the only important factor; other angles and proportions matter as well. In fact diamond cutters now use sophisticated computer modeling tools to give them a full picture of how light will behave inside a stone, allowing them to adjust proportions to optimize a diamond's brilliance, as well as its brightness, scintillation, and fire, the qualities known collectively as the diamond's "face-up appearance."

Some round diamonds come with certifications that supply their cut grade. The GIA (Gemological Institute of America) ranks diamonds as Excellent, Very Good, Good, or Fair. The AGS (American Gem Society) ranks them as Ideal, Excellent, Very Good, Good, or Fair. Amazon represents both Round GIA "Excellent cut" diamonds and Round AGS "Ideal cut" diamonds as "Ideal" on our site, since these two terms both refer to the highest quality of diamond cut.

Round cut diamonds, it should be noted, are the only ones that can achieve a grading of "Ideal." Other cuts, such as Princess, Asscher, or Emerald, will receive, at the highest, a grading of "Very Good." For diamonds that do not have AGS or GIA certifications, Amazon will calculate the cut based on the stone's depth, table percentages, symmetry and polish.

Ideal
A diamond described as Ideal represents the highest standards of cut, with only the top 3% of all diamonds falling in this category. An Ideal Cut diamond reflects nearly all the light that enters it and displays maximum brilliance and fire. For those who want the very best that money can buy, this is the cut to choose.

Very Good
A diamond described as Very Good reflects nearly as much light as an Ideal cut diamond, and represents approximately the top 15% of diamonds based on cut. The proportions may overlap with many of the proportions of an Ideal cut, with slight variations from the preferred range that allow the cutter to create a larger stone. A diamond with a Very Good cut has exceptional brilliance and is generally priced slightly lower than an Ideal cut diamond.

Good
A diamond described as Good reflects most of the light that enters it, and is much less expensive than a Very Good cut. A diamond in this category represents roughly the top 25% of diamonds based on cut. Its proportions may vary from the preferred range because the cutter has opted to maximize the size of the stone rather than creating a smaller Very Good quality diamond. For those shopping on a budget, a diamond in this range offers good quality and excellent value.

Fair
A diamond described as Fair represents the top 35% of diamonds based on cut. Though it is still a quality cut, it reflects less light and displays less brilliance than a Good Cut diamond. Diamonds in this range are typically cut to maximize size over other factors.