Diamond Cut: Determining a Diamonds Brilliance

Diamonds are naturally clear and reflect a large amount of light. However, a diamond has to be cut the right way to enhance its natural properties. The quality of a cut can make a diamond sparkle like a miniature star on your finger–or lessen its brilliance and value. Many gemologists consider cut to be the single most important factor in determining a diamond's worth–because even a perfectly transparent diamond of the rarest color will be dull, and thus less valuable, with a substandard cut.

When in their natural state, diamonds couldn't be more plain. Their surface is generally dull and pitted, covered by an opaque skin that makes it look like a lumpy, grayish stone. However, underneath the plain exterior, diamonds have a high refractive index–meaning they reflect a great deal of the light that hits them, bouncing it back. This gives the diamond its brilliance. They also have a very high dispersive power–meaning that the interior of the diamond splits the white light that enters it into its spectral colors, the way water droplets do to form a rainbow. This gives a clear, well-cut diamond those flashes of color–called fire–that can be so captivating. It takes a good cut, though, to bring out a diamond's natural brilliance and fire.

The "depth" of a diamond's cut can have an effect on the light that travels through the diamond. This generally applies to the height of a diamond when looking at it from the side, point-side down. If a diamond is cut too shallow, some light is lost at the bottom of the stone. If the diamond is cut too deep, light will escape out the sides. Both mistakes will cost a diamond in brilliance. The perfect depth ensures that as little light as possible escapes without contributing to a diamond's sparkle.

Gemologists judge the cut of a diamond by the proportions of the shape and the angles of the facets. Even with high standards, a diamond's cut can be very difficult to grade, and grading technology, standards, and practices are continually being developed. Evaluating a diamond's cut can only be accurately done by a professional grader. Different countries evaluate their diamonds based on different standards, however, which can sometimes lead to confusion for buyers.

A good diamond dealer will have their diamonds graded by an established third-party appraiser. Here are a few of the more common established companies used in the U.S.

The Gemological Institute of America (GIA). The GIA will grade your diamond's cut using one of five descriptive words: Excellent, Very Good, Good, Fair, and Poor.

American Gem Society (AGS). This company includes information on your diamond's measurements, facet angles, and depth when evaluating cut.

Holloway Cut Adviser (HGA). This company grades diamonds using a numerical system: 0-2 is excellent; 2-4 is very good; 4-6 is good; 6-8 is fair; and 8-10 is poor.

Accredited Gem Appraisers (AGA). This company is known to have some of the strictest standards on the market. They grade using a complex chart analyzing light behavior, brilliance, sparkle, and intensity.

When judging for yourself, there are a few things you can look for–even if you're not a certified gemologist. Compare the diamond you're considering to other diamonds in the store. How does it compare in terms of sparkle? Generally speaking, the greater a diamond's brilliance, the better its cut is.

In addition, consider the diamond's fire. When you look at the diamond, do you see flashes of color and depth? Or do you see a bluish-white brilliance? Colorful fire and bright-white purity are results of different proportions in the cut, and both indicate a high-quality cut–which is better is mostly a matter of taste.

Judging a diamond's cut is a complex matter, and you should look for diamonds with a certification from a known third-party grader for the best results. In addition, look for diamonds that stand out in terms of sparkle and color–chances are, these will have the highest-grade cuts.

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