Last updated on December 2, 2021
Cut quality is probably the most important characteristic of a diamond as it is the defining feature to maximize your stone’s brilliance, sparkle and overall beauty. Perhaps you have already heard the term “ideal diamond cut”, but have you ever thought about what exactly it means and how to define if the diamond you are looking at has too deep or too shallow cut?
What Is a Diamond Cut?
The cut is one of the four main characteristics (the 4 Cs) of a diamond. It refers to the precision of angles, proportions, symmetry and polish, which directly impact fire, brilliance and scintillation.
In terms of cut quality, the term “cut” should not be confused with both the diamond shape, which can be round, oval, cushion etc., and the facet arrangement which can be brilliant or step.
The Gemological Institute of America (GIA) grades round brilliant diamonds on a five-point scale of Excellent, Very Good, Good, Fair and Poor, where Excellent cut grade diamonds provide the maximum brilliance and sparkle. As for the other cuts, GIA does not provide cut grading, but some parameters help evaluate the stone’s cut quality.
The diamond cut grade is based on seven factors – brightness, fire and scintillation (how the diamond appears when viewed face-up), weight ratio and durability (how well it is designed to ensure durability and optimal weight), polish and symmetry (quality of craftsmanship). The grade is set by the lowest assessment the diamond receives for five out of the seven factors. For example, if a diamond is graded Poor for brightness, then the highest overall cut grade can be Poor. However, there are exceptions for polish and symmetry. A diamond with Very Good polish and symmetry may receive an Excellent overall cut grade.
The cut is the biggest indicator of a diamond’s beauty, and it should be made a priority over the other characteristics. A diamond with no inclusions or colour tints will still look dull if it is not cut exceptionally well. No precision, no brilliance and sparkle.
What Is an Ideal Diamond Cut?
Coined by a famous diamond cutter Marcel Tolkowsky back in the 1900s, the ideal diamond cut, also known as the Tolkowsky cut, the Tolkowsky Brilliant, the American Standard and the American Ideal Cut, refers to the proportions and angles when a diamond exhibits maximum brilliance and sparkle.
According to Tolkowsky’s calculations, a round brilliant cut diamond should be cut to the following proportions: 34.5° crown angle, 40.75° pavilion angle, 59.3% total depth, 53% table diameter, 16.2% crown height and 43.1% pavilion depth. These calculations most likely correlate to an extremely thin girdle.
An ideal cut diamond has excellent polish and symmetry and reflects almost all the light that enters it. In other words, the ideal diamond cut is the highest possible standard which is also used as a benchmark for grading all diamonds.
While Tolkowsky’s ideal cut standards serve as a global guideline for today’s diamonds, some countries have made their modifications. There are at least six “ideal cut” standards used today in the diamond industry, but only three of them, including the one by Marcel Tolkowsky, are the most common.
What Is a Deep Diamond Cut?
A diamond’s total depth or height is measured from the surface of the table to the culet, in other words, from top to bottom. This measurement is expressed as a percentage of the average girdle diameter and calculated using the following formula: Total Depth % = Total Depth (mm) / Average Girdle Diameter x 100.
Total depth percentage is one of the main factors when determining a diamond’s cut grade. When a diamond has the right combination of total depth and girdle diameter, it is more capable of reflecting light, which results in a stronger and more beautiful sparkle.
When a diamond’s total depth is too high relative to the average girdle diameter, it is said that the diamond is too deep. As a result, the light does not reflect properly, and the diamond looks less lively, having lower brightness compared to more proportional ones. In general, the deeper the cut of the stone, the duller it is.
Moreover, deep cut diamonds look smaller than ideal cut diamonds of the same carat weight when set in a mounting. This effect appears because the cutter sacrifices the stone’s width to achieve a greater depth. When the stone is set in a mounting, the additional depth is hidden as the only visible part is the diamond’s top, which is smaller than the ideal cut diamond.
What Is a Shallow Diamond Cut?
When a diamond’s total depth is too low relative to the average girdle diameter, it is said that the diamond is too shallow or spread (spready).
Shallow diamonds lack depth compared to ideal cut diamonds, which is why most of the light entering does not reflect through the table but leaks out from the bottom of the stone (pavilion), sacrificing its brilliance and sparkle.
Moreover, shallow cut diamonds tend to exhibit a “fish eye effect”, which occurs when the girdle of a diamond is reflected under the table facet. This phenomenon always detracts from the beauty of the stone.
The reason for shallow cut diamonds is to make them look bigger as from above spready diamonds look wider, and it seems that they are of larger carat weight. Sadly, some shoppers blindly focus on “bigger and cheaper” diamonds without thinking of the overall beauty of the stone and the money they waste on such stones.
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