Before you can determine the ideal proportions for a diamond, you must first determine the ideal cut. And that is, without a doubt, the round cut. Of course there are probably “ideal” ways to perform emerald, pear, or marquis cuts (just to name a few), but round cuts are renowned for providing the most brilliance and fire from any given stone, so when you are considering ideal proportions, a round cut is a prerequisite. And the perfect cut is not just a metaphor. Mathematician Marcel Tolkowsky actually calculated the precise proportions for the ideal cut in 1919 as part of his PhD research, and the results revolutionized the way the industry approached shaping diamonds.
In order to understand the perfect cut, you must first understand the parts of a diamond. To begin with, there is more than one type of cut in the round family. The brilliant cut is so called because its 58 facet design is considered the best way to showcase the brilliance of a stone, so that is the starting point for an ideally cut gemstone. The table is the flat facet on the top center of the stone, the crown would be considered the top portion of the stone (sloping upwards), the pavilion is the bottom portion (sloping down), the girdle is the edge of the stone that separates the crown from the pavilion, and the depth is the height of the stone from the point on the bottom to the top of the table.
So now that you know the parts of a diamond, here are the Tolkowsky’s magic proportions. The depth percentage (the height versus the width) should be 59% while the table percentage (the diameter of the table versus the diameter of the stone) should be 53%. The crown height percentage should be 16% and the pavilion depth percentage 43%. The girdle thickness is ideal when it is medium and even all around the stone, and perfect symmetry combined with perfectly aligned facets round out the roster. Of course, this is all more or less gibberish to the layman. And frankly, both GIA and jewelers in general quibble over these proportions (even though Tolkowsky’s science was sound). But here’s what the hype amounts to: an ideal cut creates an ideal stone in terms of the laws of physics relating to light. In short, this cut will offer the most sparkle from any given stone, which makes for one happy recipient.
