Ideal cut is a concept that is of utmost importance when deciding what kind of diamond to buy. But what exactly are the standards for ideal diamond cut, and what measurements should a stone have in order to be close to the ideal?
The Meaning of Ideal Cut
When referring to round-cut diamonds, a cut is considered ideal if its proportions allow the stone to retain and reflect as much light as possible back to the eye of the observer, maximizing the brilliance and sparkle of the diamond.
On the other hand, the further a diamond’s proportions are from the measurements that are considered ideal, the more of the light that enters the stone leaks out of it.
Since the facets of poorly cut diamonds are not well aligned to retain maximum light, such stones appear dull and lifeless.
Different Ideal Cut Standards
Although it may seem that the definition of ideal cut is uniform, there is actually no universal agreement as to what the exact ideal proportions should be.
In reality, there are at least half a dozen standards for the measurements of the ideal cut.
The most widely used benchmarks today are the American Standard, the Practical Fine Cut, and the Scandinavian Standard.
The first one is used in North America, and the other two are mainly used in Europe.
Ideal Cut Proportions
Although there are different standards for ideal cut, the proportions they use as guidelines do not differ significantly in value.
The first thing you should know about the ideal measurements is that they are expressed as percentages of the diameter of the diamond’s girdle, which is simply the stone’s edge and is also its widest part.
Let’s look at the most important measurements of an ideal-cut diamond. The numbers are given as ranges that include the standards of the most widely used benchmarks:
Table diameter: 53%-57.5% (This is the diameter of the diamond’s flat top, i.e. the table.)
Crown height: 14.4%-16.2% (This is the vertical distance from the girdle to the top of the stone; the crown is the upper part of the diamond, from the girdle to the table.)
Pavilion depth: 43.1%-43.2% (This is the vertical distance from the girdle to the bottom of the diamond; the pavilion is the lower part of the diamond, from the girdle to the lowest point.)
So, using the above numbers to derive a rule-of-thumb benchmark, we can conclude that an ideal-cut diamond should have a top that has a width of 53% to 57% of the girdle, a pavilion that is around 43% deep, and a crown that is around 14.5%-16% high.
The total height of an ideal diamond, measured from its flat top to the stone’s pointed bottom, will be around 60%, give or take 2-3 percentage points.
If you are shopping for a diamond, you most likely won’t need to measure all these values yourself: They will be included in the diamond’s grading report, and you should look them up. It is not recommended to buy diamonds that do not come with such a certificate that verifies their quality.
What about other diamond cuts?
Unlike the classic round cut, most other cuts do not have as detailed, precise, and widely accepted benchmarks against which to measure cut quality. There are guidelines, but they are much looser, and they vary from cut to cut.
What’s more, many grading labs do not grade the cut of nonround diamonds. The best way to evaluate the cut of such stones is to compare them and see which one has more brilliance as well as which diamond looks better (or even bigger) when worn.
The Diamond Cut Grading Scale: A Shortcut to Evaluation
You don’t necessarily need to examine the abovementioned measurements in detail for each stone you are looking at.
Luckily, the G.I.A. (Gemological Institute of America) does the job for you, and by taking into account a variety of standards for lengths and angles, it assigns a cut grade to each diamond it certifies.
If the diamond you are considering comes with a G.I.A. grading report, take a look at it.
The G.I.A. grades cut using the following categories: Excellent, Very Good, Good, Fair and Poor.
In general, anything that is graded Good and higher is a fine option. Avoid diamonds graded Poor; those with a Fair cut are of so-so quality, so it’s up to you to decide whether such a stone is worth it.
In case a stone doesn’t come with a certificate, assess its cut using the proportion guidelines outlined above (for round cuts only). However, we do not recommend that you buy diamonds that do not come with a grading report.
How Diamond Cut Works
Cut affects three major characteristics of a diamond that define how light interacts with the stone: brilliance, dispersion and scintillation.
Brilliance is seen when light entering the stone is reflected back to the eye of the observer. If a diamond’s depth (or height) is too high or too low, the light going into the diamond will not be reflected back to create brilliance but will instead leak out of the stone, remaining unseen.
As a result, the brilliance of too deep or too shallow diamonds is poor.
Dispersion is when the structure of the diamond breaks down the entering light into a spectrum of colors. The result is visible as play of colors when looking at the diamond and is also called “fire”.
Scintillation is the ability of a diamond to sparkle in intermittent flashes as you move it before your eyes. A well-cut stone exhibits a lot of sparkle, whereas a poorly cut one looks much less lively.
How Important Is It to Buy an Ideal-Cut Diamond?
The closer the cut of a round diamond is to the ideal cut, the higher the stone’s brilliance will be.
Diamonds with poor cuts look less bright and appear lifeless, not to mention that because of the diminished brightness, their flaws and color tints become more visible.
So, it is usually a good idea to pay more money for an ideal cut.
However, going one grade lower than the ideal does not usually result in a visible difference in the appearance of the diamond.
It is not recommended to go much lower, though, so don’t expect much in terms of brilliance from stones at the lower end of the scale.