Lab-Grown Diamond Cut – Why it matters more than anything else

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Introduction to Diamond Cut

Cutting a diamond means transforming it from its raw state of being a lump of carbon atoms into the gemstone that adorns jewelry. Lab-grown diamond cut and its grading are concerned with how well a diamond’s cut proportions interact with light and thus are directly correlated with the sparkle of a diamond.

Diamond cut is the most important of the lab-grown diamond 4Cs. It’s by far the most significant contributor to the “sparkle,” which in turn is the essence of a diamond. For that reason, you should never compromise on lab-grown diamond cut quality.

Lab-grown diamond cut is determined by the raw stone and the skillset of the master diamond cutter

Lab-grown diamond cut is exactly the same as for mined diamonds. In fact, lab-grown diamonds are exactly the same as mined diamonds. Except lab-created diamonds are made in a lab instead of being pulled out of the earth. In addition, lab-grown diamonds are at least 60-80% cheaper than mined diamonds (even cheaper if you get them during a lab-grown diamond sale).

And, perhaps, most importantly, lab-grown diamonds are better for the environment, climate, and society. Learn more about the ethical diamond choice.

Before we move on, we should note that diamond sparkle or brilliance are the most common terms used to describe the diamond light interaction, but technically is divided into three effects:

  • Brightness: How white light is reflected internally and externally
  • Fire: How white light reflected by the diamond turns into rays of all colors of the rainbow
  • Scintillation: How much a diamond “glitters” or “shines” (for lack of better words) as well as areas appearing dark

For simplicity, we’ll refer to all these effects as sparkle or brilliance.

Our 3 favorite diamond jewelers for the best lab-grown diamond cut quality

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Why you should care

Simple: Diamond cut grade is the most critical factor in determining the “sparkle,” which makes diamonds unique. If you’re not concerned with the brilliance, then you’ll probably be better off with another type of gemstone. But since you’re here, we’ll assume that’s not the case.

The most important aspect of the lab-grown diamond cut is how light is reflected. Lab-grown diamond cuts are highly complex and are designed to reflect as much light as possible to maximize the “sparkle” of the diamond. This requires the stone to be cut at certain angles and that the depth-to-surface and other ratios are exactly right.

If you buy a fancy-shaped diamond (that is, anything but a round brilliant), the chances are that the cut will not be graded. However, if you are in the market for a fancy-shaped diamond, you can jump to this section to learn why they are often not graded.

Mined vs. lab-grown diamond cut

Mined and lab-grown diamonds are cut in precisely the same way. While the raw stone may differ in shape, the process is exactly the same. It is just as challenging to create a perfect stone from a lab-grown diamond and maximize the light reflection and brilliance. The complex and demanding, labor-intensive cutting process is one reason that even as lab-grown diamonds decrease in price, they will never be cheap.

This explains why the cut is the most critical aspect of the diamond and why a high-grade cut is more expensive. It requires hours of highly skilled labor and compromises the size and carat weight of the finished diamond. However, since the cut is independent of how the diamond was created, the diamond cut and what you pay for it are exactly the same for mined and lab-grown diamonds. It also explains why diamonds will always be costly and hold good value even as prices fall.

Lab-grown diamond cut from a raw piece of rock

Diamond shapes vs. cut

What is the difference between diamond shape and diamond cut? The diamond cut should not be confused with diamond shapes, but it often is. The shape determines whether the diamond is round, oval, or even heart-shaped. The diamond cut is related to how well the diamond has been cut into whatever particular shape it is supposed to be. Learn more about lab-grown diamond shapes.

Lab-grown diamond can be cut into many shapes, however diamond cut and diamond shape does not refer to the same

How to evaluate lab diamond cut quality

When evaluating the lab-grown diamond cut grade (of round diamonds, see below regarding fancy-shaped grading), the diamond proportions are compared to the ideal proportions. The ideal proportions are based on Marcel Tolkowsky’s mathematically derived ideal shape and cut of the round brilliant. His model is the base of the 57-faceted ideal cut. However, it has since been tweaked based on computer simulations and surveys – notably by GIA, the diamond grader and inventor of the 4Cs.

However, while there is an ideal model and ideal proportions, the grading of diamonds is still subjective and will vary between laboratories and individual graders. There are two key reasons for this:

  1. The adjustments made to the Tolkowsky model vary slightly between laboratories, even though they are very similar.
  2. The grading of the diamond cut is carried out by people. While assisted by modern technology, the final assessment and grade are still set by a human. And humans are inherently imperfect.
Lab-grown diamond cut is the number one determinant of diamond quality and light reflection.
Every angle and every proportion matters and must follow strict guidelines to get as close as possible to the ideal diamond cut

Should I worry about the diamond cut grading variance?

In short: Not too much. The most reputable diamond grading laboratories have stringent guidelines and standards. The variation between the top laboratories and their grading is only very slight. Aiming for an ideal or excellent cut coupled with a visual inspection looking at the HD images, you can rest assured that you will get a high-quality stone (visit Clean Origin, Ritani, or James Allen to ensure access to HD diamond images). As you can read below, you have to be aware that GIA’s top grade is Excellent, while AGS and IGI have a further tier called Ideal.

Who evaluates the cut?

Grading laboratories carry out the grading of the lab-grown diamond cut. The most well-known grading institute, and inventor of the 4Cs, is the Gemological Institute Of America (GIA). Another often-used grading lab, in particular in the US, is the American Gem Society (AGS). Lastly, the International Gemological Institute (IGI) has established itself as the premier grader of lab-grown diamonds. The reason is that they grade lab-created stones in more detail than, for example, GIA does.

One crucial thing to note is that while GIA (who came up with the scale) tops out at the Excellent cut grade, both AGS and IGI’s best grade is Ideal. So when you’re evaluating a diamond graded by GIA, aim for an excellent grade. When graded by IGI, which is most likely with a lab-grown diamond, go for ideal and downgrade only to excellent if you cannot compromise on any of the other three Cs.

The lab-grown diamond cut grade is determined in a laboratory by an independent grading institute.

Benefits of choosing the best diamond cut grade

When choosing an excellent or ideal cut diamond, you not only maximize the brilliance you get, but you also allow yourself to downgrade on some of the other diamond parameters without it being noticeable – except for the price tag. You can learn exactly how much by reading our step-by-step lab-grown diamond buying guide here. Suffice it to say picking the best cut grade pays off in many ways.

Why are fancy shapes not cut-graded?

Fancy-shaped diamonds do traditionally not receive a cut grade from the grading laboratories for two reasons.

  1. Fancy-cut diamonds are usually not chosen for their brilliance alone since all other shapes than round compromise on sparkle by default. In order to improve the brilliance of a fancy-shaped diamond, you would have to make it more round. So the ideal shape of a cushion-shaped diamond would actually be to get rid of its squareness. Completely.
  2. The second reason is that the number of different shapes and their variations are almost infinite. Unlike the round shape, where the ideal shape is *drum-roll* round, fancy-shaped diamonds are shaped in various forms for design and aesthetic reasons (other than brilliance).

While some “ideal” proportions do exist, there is no consensus on the exact measurements, and they are more like ideal ranges.

How to evaluate fancy-shaped diamonds’ cut grade?

Some laboratories currently offer fancy-cut grading, namely IGI, the premier grading institute of lab-grown diamonds. The challenge is that there are no common standards, and it’s challenging to hold laboratories accountable and compare diamonds graded by different institutes. So use the laboratory grading as a guide (choose excellent or ideal) but know that it’s not as reliable as with round brilliants.

To overcome this limitation, you should always shop at a reputable diamond seller and only places that give you access to the diamond certificates – before you buy. They offer high-quality, high-definition 360-degree images where you can carry out your own inspection of the stone’s sparkle. You could also compare the diamond’s propositions against the ideal cut of the particular shape.

Another approach is to use an Angular Spectrum Evaluation Tool (ASET) to inspect light reflection. This is a commonly used tool across the diamond industry. However, not for consumers. Unfortunately, very few online sellers offer images taken using the ASET tool. One of these is James Allen, but you will have to ask their gemologists if they have it available. However, for most consumers, you can make do with a lab grading (when available) coupled with a visual inspection of HD images.

Why aren’t all cuts just excellent?

The excellent GIA cut (or ideal by IGI and AGS) requires precise proportions, which the raw diamond may not lend itself to. It may require that too much be cut away, lowering the carat weight. Sometimes the cutter tries to cut around an inclusion which further can compromise the ideal proportions. In most cases, the cutter will have to balance clarity, cut, and carat to maximize the price.

The “problem” is that not everyone is as educated as you and, therefore, may have a preference for higher carat weight (vainly) over the diamond cut or hold a false belief that a diamond should be flawless. As you can read more about in our buying guide, you would rarely want to pick the highest color and clarity grade. Sacrificing carats for a better cut will make the diamond appear larger (and appearance is everything – not size).

The art of the lab-grown diamond cut requires precision tools, skillful mastery, and many years of experience.

Lab-grown diamond cut buying tips

This is probably the most uncomplicated advice we offer: Choose the best cut grade every time. If graded by GIA, choose the excellent diamond cut grade. If graded by one of the laboratories, such as IGI, then choose the ideal lab-grown diamond cut grade. Always, always, always maximize the cut grade of the stone you’re buying and compromise instead on color, clarity, or, ideally, carat. We recommend that you don’t go below excellent or ideal cut.

Read all of our buying tips in our step-by-step guide to purchasing a lab-grown diamond here.

Where to shop for the best lab-grown diamond cut quality?

We review lab-grown diamond jewelers, and we have listed the best places to buy lab-grown diamonds. Shopping for an engagement ring? See our top-rated places to buy a lab-grown diamond engagement ring. See also our updated guide to buying a lab-grown diamond engagement ring.

Read more tips in our guide to buying lab-grown diamonds.

Our 3 favorite diamond jewelers for the best lab-grown diamond cut quality
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Rolf Hartmann
Rolf Hartmann

Rolf Hartmann has decades of experience in the jewelry industry. He knows everything you need to know to find the perfect diamond. He's an expert in lab-grown diamonds and has followed the exciting development of lab diamonds from industrial usage to the incredible gemstone quality that lab-grown diamonds are today. Rolf guides you to find the right diamond at the best possible price and expertly and transparently reviews all lab-grown diamond sellers.

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