Diamond Cut

Diamond cut is one of the “four Cs” used to determine the overall quality, and therefore the price, of a diamond. Most diamond certificates will include a rating of the diamond’s cut, and, all other things being equal, a diamond with a better cut grade will command a higher price.

While the other three criteria (clarity, color, and carat weight) are relatively straightforward and simple enough that they can be understood and assessed by anyone, cut is a much more complex variable.

The methods for determining a diamond’s cut rating can vary depending on who is making the assessment, and, to further complicate the matter from the buyer’s perspective, some certificates don’t explain in much detail what criteria they used to grade a diamond’s cut.

That being said, if you’re thinking of buying a diamond, it would be well worth the time it takes to understand what different cut grades mean, how they’re determined, and what influence they have on a diamond’s price. This knowledge makes you better able to determine for yourself what a diamond’s price should be, distinguish a good deal from a bad one, and make the best possible investment when buying diamonds.

What is diamond cut?

In simple terms, the cut grade of a diamond refers to the “light performance” of a diamond, meaning the degree to which the diamond retains and reflects the light that enters it. A diamond with a good cut will be highly reflective and exhibit the best possible amount of sparkle. Conversely, diamonds that “leak” light through the bottom or side are usually cut too shallow or deep respectively, and they will thus have a less favourable cut grade.

Since it’s widely acknowledged that the aforementioned diamond rings sparkle or brilliance is what gives diamonds their unique beauty, it follows that cut is what separates the most stunning diamonds from just ordinary ones.

It should be noted that “cut” in this sense does not refer to the intended shape of the diamond. If you’ve ever browsed for diamonds, you’ve probably come across terms like “Princess cut,” “Asscher cut,” “Emerald cut,” and so on. These refer only to stylized diamond shapes, and are not an indication of a cut rating.

What diamond cut grades are there?

At this point there still isn’t a standardized system for diamond cut grades. Each certifying authority uses its own system to rate the cut of a diamond, which can make things slightly confusing. Thankfully, however, the grades themselves are usually fairly self-explanatory, even if the methods used to determine them aren’t all that clear (more on that later).

Most certifiers use a five or six-point cut grading system. The typical system goes as follows, from best to worst:

Ideal: A diamond with maximum brilliance.
Premium: Nearly equal to Ideal.
Very Good: A diamond with slight light leakage.
Good: A diamond with decent reflectiveness, usually one which has been cut for size rather than brilliance.
Fair or Poor: Diamonds that reflect relatively little light.

Again, though, in some cases the terminology that is used can differ, the Gemological Institute of America, one of the major diamond rating authorities, for example, grades diamond cuts as Excellent, Very Good, Good, Fair, and Poor; so, diamond cuts rated “Excellent” by the GIA will be roughly equivalent to those rated “Ideal” by other bodies. Additionally, some diamond vendors have a special designation for their best cuts. For example, the online diamond retailer Blue Nile has a “Blue Nile Signature Ideal” cut, a term which they use to refer to cuts within the top 1%.

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