Understanding Diamond Cut

Does your diamond jewelry make the cut? Learn about the most misunderstood but most important of the Four C’s.

Like most gemstones, diamonds require cutting and polishing. The skill of a diamond cutter is required to unlock the extraordinary and unique beauty of a diamond. Many gemologists believe this is the most important – though most misunderstood – of The Four “C”s that determine a diamond’s quality and value. Even if a diamond has perfect color and clarity, a poor cut will cause it to lose sparkle.

Cut refers to the execution of a diamond’s design, the skill with which it was cut, the quality of its polish, and the overall symmetry of the stone. Key factors include the stone’s roundness, depth, width, and the uniformity of its facets.

Cut is also used to describe the shape of a diamond. In addition to the round brilliant, other popular cuts include emerald, marquis, pear, oval and square.

Each diamond is cut according to an exact mathematical formula. The most common cut, the round brilliant, has 58 facets, or small, flat, polished planes designed to yield the maximum amount of light to be reflected back to the viewer. This reflection, known as brilliance, is an extremely important factor in evaluating the quality of a diamond.

Although there are several systems for determining the quality of a diamond’s cut, they can be broadly characterized as Ideal, Excellent, Very Good, Good, Fair or Poor. Ideal and excellent cuts represent the top of the line; most or all of the light that enters the diamond is reflected back to the eye. A stone with a very good or good cut grade reflects nearly as much light as the idea
and excellent cuts, but is available at a lower price. Fair cuts are still considered quality diamonds, but have considerably less brilliance than good cut grades. And a poor cut is a diamond which is off in its proportions and subsequently loses most of its light out the sides and bottom.

In other words, a well-cut diamond has the right angles and proportions to release the inner brilliance of the stone and project its maximum amount of fire and sparkle. A poorly cut diamond is a “dull” diamond that may even have some “dead” spots inside.

A diamond’s proportions, particularly the depth compared to the diameter, and the diameter of the table (the largest and topmost facet of the diamond) determine how well light will travel within the diamond and back to the eye.

Two keys to a diamond’s brilliance are its crown and pavilion. The crown is the top portion of a diamond extending from the girdle (the outermost edge of a cut gem) to the table. The pavilion is the part of the diamond below the girdle. Above the girdle of a brilliant cut diamond are 32 facets plus the table. Below the girdle are 24 facets plus the culet, or point. Just a few degrees off the
standard can have a drastic impact on a stone’s brilliance. But there is some leeway. Cutters can compensate by adjusting crown angles, table sizes and pavilion angles to produce the best possible results for each stone.

 

Diagram of a Diamond Cut too Deep Diagram: Diamond Cut Depth Diagram of a Diamond Cut too Shallow
Diagram of Diamond Table Cut Diagram of Ideal-Cut Diamond

 

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