Whether you’re on the hunt for the perfect diamond engagement ring or trying to evaluate antique diamond jewelry, there’s a lot to consider before making your decision. So many different factors go into grading and valuing diamonds, and it can all seem a bit overwhelming at first glance—but don’t worry! We’re here to make it easy.

You may have heard of something called “The 4C’s,” which is a short-hand way of describing the four major qualities used to assess a diamond’s value: cut, color, clarity and carat-weight. In fact, you may have read our overview of this process here! But if you’re still wondering exactly how to make sense of it all, we’ll be giving you an in-depth look at each quality over the next few weeks right here on our blog.

Today we’re going to go over Cut, which is probably the most complicated—and sometimes underrated—of all the diamond grading qualities.

Cut Style vs. Cut Quality

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When you hear the term “cut” in relation to diamonds, it can refer to two different things. First, there’s the shape and faceting style, which is typically categorized as either “round brilliant cut” or “fancy cut.” Second, there’s the cut quality—the diamond’s proportions, symmetry and polish—which is what “cut” refers to in the 4C’s. However, that doesn’t mean that cut style has no effect on value.

There’s a vast variety of cut styles available today, allowing more individuality than ever in jewelry making. You’re probably familiar with the classic round brilliant cut and popular fancy cuts like the emerald or princess cut, but if you dabble in antique or custom jewelry you’re likely to come across styles you won’t find in your average jewelry store! Antique styles like the rose cut or mine cut are rare today, while modern diamond cutters have been producing completely new styles that resemble flowers, butterflies, and more!

Though you should always choose the diamond cut style that suits your personal preference, it’s good to keep in mind that the relative popularity of certain shapes and how labor-intensive cutting can be has an effect on value. The round brilliant cut has been the most popular shape for over a century, and lots of time and energy has been put into making sure it is cut to exacting standards. Therefore, it’s no surprise that its price reflects its special status. For example, a round brilliant cut diamond with the exact same 4C’s grade as a marquise cut diamond will actually cost more. Likewise, especially rare and unique cuts will also fetch more on the market.

All that being said, the actual cut quality—no matter the shape chosen—has the most impact on overall value, so let’s take a look at how it’s graded.

Cut Quality

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The cut quality of a diamond really stands out in the 4C’s because it has the greatest single influence over the brilliance of the stone—plus, with the exception of lab-grown diamonds, it’s the only quality we have much control over! A skilled gem cutter can make all the difference in the world when it comes to bringing out a diamond’s signature beauty.

As specified above, cut quality is determined by proportions, symmetry, and polish. Today, diamond cutters use precision instruments so that ideal proportions and angles can be achieved which maximize the brilliance (reflection), dispersion (fire) and scintillation (sparkle) of the diamond. Basically, all those facets (flat, polished surfaces) gather light from all directions and then reflect it back to us, producing that dazzling effect only a well-cut diamond can produce! Let’s dive a little deeper into just how that dazzle is measured.

Brilliance

Brilliance is the total intensity or amount of light that is reflected from both the diamond’s surface and interior. The awesome thing about transparent gemstones is that light isn’t just reflecting off the surface—like it does on pearls or jade—it’s also being reflected from inside the stone!

Dispersion

Dispersion is what happens when white light is split into a rainbow effect, like what you see when light enters a prism. When it comes to diamonds, this stunning display of color is known as “fire.”

Scintillation

Scintillation sounds complicated, but it’s really just that dazzling sparkle you see when you move a diamond around! The sparkling can vary based on the pattern of light and dark areas in the diamond.

Those are the basic optical effects a diamond grader is looking for, but the grading process actually gets much more technical as it proceeds. Taking a look at the anatomy of a cut diamond will help show us just how precise it gets and why these technical details not only maximize the beauty of the diamond, but also play an important role in its durability.

Features of Cut

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Almost all cut diamonds have two main parts: the crown (the upper part) and the pavilion (the lower part). The angles and depths of these two parts are measured against ideal percentages which have been found to produce the most dazzling effects. Where the crown and pavilion meet is called the girdle, which is the widest part of the diamond. The width of the girdle is important because it acts as the setting edge when the diamond is secured in a piece of jewelry, but a balance must be struck.

If the girdle is too thick, the diamond will appear smaller than its carat-weight would seem to indicate and may actually be difficult to set into jewelry. However, if the girdle is too thin, the diamond will be at an increased risk of chipping which is a major risk to the longevity of the stone. Therefore, a width somewhere in the middle is usually preferred, with round brilliant cuts leaning more towards a thinner girdle and fancy cuts leaning more towards a thicker girdle.

Similarly, the culet facet—which is a cut at the base of the diamond—shouldn’t be too small or too big. Too small (or nonexistent) and it won’t protect the base of the diamond from chipping. Too large, however, and it will appear to be a big black spot in the middle of the diamond!

Overall, the main thing a diamond grader is looking for here is symmetry and proportion in accordance with the ideals for each shape. Is the table slightly off-set or precisely centered? Is the girdle wavy or perfectly straight? Are the crown angles exactly the same around the entire diamond or do they vary? Is the pavilion angle too steep or too shallow? The more symmetrical, proportional and ideal these measurements are, the higher the diamond will be graded. Let’s take a look at what those grades actually are.

Cut Grades

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The Gemological Institute of America (GIA) has developed the strictest diamond grading scale, and it’s their standards we’re going to go by here. Diamond cuts are graded on a scale of Excellent to Poor, taking into account all the factors detailed above. The profile diagrams next to each diamond in our example will help us compare and contrast each stone and easily see why their grades vary so much.

For example, when comparing the Excellent diamond against the Good diamond, you may notice that the Good example has a shallower crown and pavilion, which contribute to its poorer optical performance (note how much darker the Good example appears when compared to the Excellent example). You may also notice that the pattern of dark and light areas in the Good example are not as symmetrical as in the Excellent example.

All of these issues are especially pronounced in the Poor example—we can see that not only are the proportions quite different from the others, but that the girdle is extremely thick as well. The result? A rather dark diamond that will appear smaller than its carat-weight would suggest and will never sparkle quite like the others. These are the tell-tale signs of a poor-quality cut.

The other quality a diamond grader would be looking at is the polish of the diamond’s facets. Basically, the facets should be smooth and lustrous, or else the diamond’s reflections won’t be crisp and can even contribute to trapping oil and dirt—major hindrances to achieving that coveted sparkle! Indeed, a poor polish job will make an otherwise lovely diamond look quite dull.

All of these factors are studied under microscopes, carefully measured, and then precisely calculated before assigning the diamond its final cut grade. As you might expect, the higher the cut grade, the higher the value of the diamond will soar. However, it’s not just because Excellent and Very Good diamonds are more dazzling; it’s also because they necessitate sacrificing more of the original raw diamond. Every facet has a cost, and a quality cut ensures that these sacrifices are not in vain.

Check out the interactive tool below to see even more detailed examples of all the cut grades!

Bottom Line

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Cut quality doesn’t always receive the love it deserves when it comes to producing dazzling diamonds, but now you know how important it really is! The standards of diamond cutting are no accident—they’re our human contribution to these gorgeous gifts from nature. Combining all we’ve learned about mathematical angles, proportions, and the interplay of light, we can shape these stunning objects of fascination and desire, revealing more and more of their unrivaled beauty as the field of diamond cutting continues to advance.

Next up, we’ll tackle the grading process for Color, so make sure to check back soon! In the meantime, why not stop by one of our stores and see our collection of loose diamonds and diamond jewelry up close and personal—even under our microscope! Or, you can view our extensive diamond collection online here and our diamond jewelry here!