Diamond Cut Education: Factors, Grades, Buying Tips & More

Cut: the most crucial of the 4Cs...

Diamond buying requires extensive research, and most information revolves around the 4Cs. The 4Cs are the hallmarks that determine a diamond’s overall quality.

But, which of the 4Cs is the most important, and why?

👉🏻A diamond’s cut is its most important characteristic, and a Poor or Excellent cut can completely change how a diamond shines. When we imagine a diamond, we picture brilliant white fire within its surface. Cut is pivotal to that fire, and finding a diamond with the right cut for you can be tricky. Let’s discuss how to identify diamond cuts and shop accordingly.

What is “diamond cut”? 

People love diamonds because of their sparkle, and much of that glittering fire comes from the way light moves through the surfaces of the gem. Cut refers to how these surfaces, or “facets”, reflect and refract light. It is a mathematical combination of several factors, including polish, symmetry, proportion, and more!

A well-cut diamond will send light through the stone and out of the table. In contrast, a poor cut may cause light leakage, where beams are directed through the bottom or sides of the diamond. In this case, the table of the diamond is darker, duller, and much less appealing.  

Quality Diamond Cut With a High Grading

As mentioned above, cut is the most important characteristic of a diamond. This is because cut dictates the pathways of the very essence of a diamond’s sparkle: light. Without properly dispersed light, there would be no shine. 💡Cut is the foundation of a quality diamond, and it’s definitely something to consider as you shop.

Diamond cut vs. diamond shape: what’s the difference?

Finding the perfect cut depends on multiple factors, one of which is a diamond’s shape. Although the two terms are often used interchangeably, they speak to two very different characteristics of a diamond.

As we just discussed, a diamond’s cut is the measure of how well a stone’s facets are crafted, arranged, and polished. However, a diamond’s shape is the literal outline of the stone. A diamond’s shape can vary, and some popular shapes include round, square, emerald, oval, marquise, etc.  

On the other hand, there are fewer types of diamond cuts, including brillant, step, and mixed. We’ll learn more about these types of diamond cuts below.

What factors impact diamond cut, and how?

Diamond cut styles

Diamonds are mainly cut three different ways. Here is a breakdown of each:

Brilliant cut

The most popular cut style, brilliant-cut diamonds consist of 57 to 58 triangular and kite-shaped facets. How many facets the diamond has depends on whether the stone’s culet is faceted or pointed. This cut is optimized for scintillation, and light travels efficiently through the stone’s facets. The round brilliant cut diamond is the most popular example, making up almost 75% of diamonds sold.📊 However, you’ll also find brilliant-cut marquise, cushion, pear, oval, and heart-shaped diamonds.

Step cut

Edgy yet elegant, step cut diamonds have become increasingly popular in the last decade. This cut requires trapezoidal facets, and they run parallel to the girdle, steadily decreasing in size to the culet. As such, this cut allows for a wide diamond table, which makes color and clarity important. You’ll typically see a step cut on emerald shapes, but baguette and Asscher shapes may also have a step cut style.

Mixed cut

For those buyers who seek the best of both worlds, mixed cuts are a favorable option. Mixed cuts combine elements of both brilliant and step cuts in a few different ways. The top of the stone may have brilliant facets and the bottom may have step cuts, or it can be the opposite! Many jewelry retailers create their own style of mixed cut that they market to customers seeking something more unique.

The perceptive factors of diamond cut

The perspective factors of diamond cut are brilliance, fire, and scintillation, and they directly impact a diamond’s grade.

Perceptive Diamond Cut Factors

FactorDefinition
BrillianceHow bright a diamond appears based on the amount of white light emanating from it
FireDispersion of light into multiple colors, seen as flashes within the light moving through the diamond
ScintillationBright flashes of light and dark that create sparkle

If a diamond’s cut is poor, light will not interact with the facets correctly and all three perceptive factors can be affected. Here are some examples:

Too deep

Too Deep Diamond Cut

When a diamond’s cut is too deep, light bounces off one facet at a steep angle and then the next facet at a very low angle. As a result, light refracts through the second facet and shines out of the bottom of the diamond. Because the light does not reach the gem’s surface, the diamond has a “nailhead” or a large, dark spot in its table.

Too shallow

Too Shallow Diamond Cut

If a diamond’s cut is too shallow, light passes through the stone and refracts off the pavilion facets at a low angle, exiting through the bottom of the diamond. Because the light does not reach the top facets of the stone, wearers experience an effect called “fisheye”, where a dark halo surrounds the diamond’s table.

Just right/Ideal

Just Right / Ideal Cut Diamond

When a diamond has an Excellent cut, light hits the pavilion facets and refracts upward through the table at a steep angle, and our eyes receive this light as a diamond’s brilliant fire.✨

The technical factors of diamond cut

The technical factors dictate how much we perceive brilliance, fire, and scintillation. The three technical factors are proportions, symmetry, and polish, and they are the crucial code by which gem cutters craft diamonds.

Proportions

The proportions of a diamond’s parts and their relative angles impact a diamond’s shine. Without the right proportions, a diamond’s facets cannot properly reflect light through its surface. Three very important proportions for any diamond are the width, depth, and size of the table.

Different Proportions of a Diamond (GIA)
Diagram: GIA (Gemological Institute of America)

👉🏻These measurements are then used to calculate important percentages that dictate the quality of a diamond. Examples include the length to width ratio, depth percentage, and table percentage.  

Ideal proportions can vary by diamond shape. For a round brilliant diamond, the following proportions would produce an ideal gem:

  • Depth Percentage: 59 - 62.6%
  • Table Percentage: 54 - 57%
  • Girdle Thickness: Thin to Slightly Thick
  • Culet: None to Pointed
  • Length to Width Ratio: 1.0 - 1.03

Symmetry

Facet placement produces the angles necessary for a diamond’s sparkle, and symmetry measures the size and precision of facet placement. Facets both above and below a diamond’s girdle impact how light will reflect and refract through the stone. If a diamond has too many facets, a missing facet, or misshapen facets, it might be noticeable!

Polish

Polish measures the shine and surface condition of a diamond’s facets. Facets should be smooth and clear to provide the best mirror for reflected light, and a dull facet can cause light to filter through other areas of the stone.

Although gem gutters do their best to craft diamonds with precise shapes, they cannot always remove imperfections. 💡Some imperfections are a byproduct of diamond cutting, and they can include abrasions, burns, nicks, scratches and more. These flaws may be seen at 10x magnification, so be sure to inspect your diamonds closely!

Diamond cut grade chart (With pics)

It can be difficult for buyers to tell how well a diamond is cut, but the GIA cut grading scale makes things a bit easier. The grading scale measures diamond cuts with grades of Excellent, Very Good, Good, Fair, and Poor. The scale notes the presence of dark spots, missing light, and other abnormalities within a diamond’s sparkle to distinguish between grades.

Here is a cut grade chart that explains the GIA scale:

Diamond Cut Grades

GradePictureDescription
Excellent Excellent Cut 1 Carat G-VS1 Round Diamond - James Allen 10189808
SKU*: 10189808

A diamond has minimal imperfections, and the patterns of bright and dark spots are even. Light shines properly through the stone, and any flaws that could impact grade are not present.

NOTE: This category is labeled as "Ideal" on the AGS scale.

Very GoodVery Good Cut 1 Carat G-VS1 Diamond (James Allen 8835385)
SKU*: 8835385

A diamond’s scintillation, fire, and brilliance are slightly affected by its cut. Factors such as weight and proportion ratios aren’t completely off, but the way they interact causes changes in the way light moves through the stone. Gemologists may notice darker spots in the diamond’s surface or even a less desirable pattern within the table.

GoodGood Cut 1 Carat G-VS1 Diamond (James Allen SKU 9825431)
SKU*: 9825431

These diamonds are visibly less bright, and improper measurements and angles affect scintillation and fire. Larger areas of darkness are visible on a diamond’s table, and there may also be a lack of contrast as white light is muted.

Fair-

Steep or shallow cuts, bad angles, or disproportionate weights characterize diamonds in this category. They have localized darkness across their table, lack contrast, and experience large problems like fisheyes.

Poor-

Issues with poor diamonds are serious, such as very steep angles, incredibly thick girdles, or misleading carat weights due to bad cuts. These diamonds are dark, with little light escaping through their tables.

Note: *Diamonds in the chart are from James Allen; these diamonds have the same carat, color and clarity gradings: 1 carat, G and VS1.

Unique cut grading scales of leading retailers

Some diamond retailers have custom ”premium cuts” that they use for their collections.  Here are two popular retailers, James Allen and Blue Nile, that have their own, high quality cuts:

James Allen

James Allen carries a “True Hearts” collection that focuses on some romantic features of a diamond’s shine: hearts and arrows. 💃🏻

This collection includes round, cushion, and princess cut stones crafted in a precise way that includes a pattern of hearts and arrows. 🔍When viewing the diamond from above, you can see sharp arrows. In contrast, when viewing the same stone from below, you’ll see sleek, pointed hearts. A true hearts and arrows pattern on a diamond requires exquisite optical symmetry, and the design creates great light return that improves fire, brilliance, and scintillation.

Arrow and Heart Patterns of a Diamond From James Allen's True Hearts Collection
Seen from above (L) and seen from below (R)

While the idea of a hearts and arrows diamond suggests at least an excellent cut diamond, buyers are encouraged to examine the stones themselves to ensure they are of good quality. Because of the difficulty of making each heart and arrow identical to others, there are sometimes minor imperfections in the patterns of some stones.

James Allen offers idealscope images for buyers to inspect a diamond’s light return, and their gemologists are always on hand to explain any diamond.

Blue Nile

Blue Nile boasts their Astor collection as a selection of diamonds with exceptional standards. According to their website, the raw stone used for these diamonds is of excellent quality, with few inclusions or defects. The stones are then cut with precise requirements to enhance light reflection and promote superior fire, brilliance, and scintillation.

Whether or not these diamonds are better than Excellent cut stones, Blue Nile gives you the tools to make your own decisions. Astor diamonds are graded by the GIA and certified by GemEx. Additionally, Blue Nile offers 360° views of all diamonds and up-close images so you can inspect your gems. Blue Nile also offers professional advice 24/7, so you’re always an online chat or phone call away from a trained gemologist’s opinion.

Grading scales for symmetry and polish

Typically listed as “additional grading information” on a GIA diamond grading report, symmetry and polish grades are part of the bigger picture of diamond cut quality.

These grades also impact the overall cut grade by the GIA, and they are taken into account when deciding where a diamond falls on the scale. However, it can be helpful to know these individual symmetry and polish grades for a more precise inspection of your diamond. Doing so can help you identify any flaws and ensure you are getting a good value for your budget.

Symmetry

Gemologists measure diamond symmetry on a scale from Excellent to Poor. These grades are based on a careful inspection of the stone’s proportions and facets. Common imperfections may include crown angle variations, off-center culets, extra facets, girdle thickness variation, uneven corners/edges, and more.

GIA Symmetry Grading Scale

GradeDescription
ExcellentThere are no flaws or miniscule flaws that are not visible under 10x magnification and do not affect a diamond’s appearance.
Very GoodMinor flaws are visible under 10x magnification, but they do not affect a diamond’s appearance.
GoodFlaws are detectable under 10x magnification, and some of them can impact a diamond’s visual appeal.
FairThe diamond has obvious symmetry flaws that affect its appearance.
PoorThe flaws on a diamond are obvious without magnification and greatly impact its visual appeal.

Polish

✅Almost all diamonds have some form of polish defect, as marks on the surface of a gem are side effects of being hand cut. However, most polish flaws aren’t visible without magnification, and the most important factor is whether or not they penetrate deeper into a diamond. Even diamonds with excellent polish can have minor polish flaws, as they are allowed so long as they don’t affect the gem’s luster.

GIA Polish Grading Scale

GradeDescription
ExcellentNo imperfections or none that affect light return. They’re hard to see at 10x magnification.
Very GoodAt 10x magnification, small flaws may be visible when the diamond is face up.
GoodThere are detectable flaws that can be seen under 10x magnification and may impact luster.
FairThere are easily detected flaws at 10x magnification, and a diamond’s luster is impacted.
PoorFlaws are noticeable without magnification, and they greatly impact luster.

Taking diamond cut, the other 3Cs, and additional factors into account

So how should diamond cut factor into your buying decisions?  Here are some ways cut impacts other areas of your purchase:

Price

Higher quality diamonds are typically more expensive, and proportions, symmetry, and polish all play a role in increasing a diamond’s value. In fact, the more perfect the diamond, the higher the price will be!  

Because cut directly influences light return, a high quality cut is crucial for ideal fire, brilliance, and scintillation. It’s the most important of the 4Cs when searching for a diamond, so plan your budget accordingly!

Color and clarity

With diamonds, color and clarity are less important than a quality cut. This is because an Excellent cut can actually improve a stone with a yellowish tint or less than ideal clarity.

A Very Good or Excellent cut can mask inclusions and improve the face up color of a diamond. In contrast, a diamond with a Poor cut and Excellent color and clarity will still look dull, as light does not properly travel through the gem. ⚠️Be sure to prioritize cut when shopping for your diamond!

Carat

As the carat weight of a diamond increases, so does the price. This is true of cut quality as well, and both factors can drastically affect a diamond’s value. However, it’s important to balance the two characteristics to find the right stone for you.

Oftentimes, gem cutters will sacrifice Excellent cut to produce a diamond with a heavier carat weight, as many buyers will just purchase the largest stone they can afford. As such, when shopping on a budget, it’s usually a better idea to opt for a smaller, Excellent cut diamond than purchase a larger, lower quality stone. While the latter may be larger in size, the former will have more shine and dazzle in the right setting.

Setting

While shopping, consider what type of setting you would like for your diamond, as it will impact its visual appeal.

For instance, if you want a solitaire setting, make sure you get a diamond with a Very Good or Excellent cut. Your diamond will be the center of attention in your setting, so you’ll need to ensure it sparkles brilliantly. In contrast, if you’re opting for a halo setting, you can sacrifice a bit of quality if necessary. Because your diamond will be surrounded by others, it’s less important to make sure your diamond can stand alone, as it will have the helpful shine of smaller stones.  

You should also consider the color of the metal you choose for your setting. White metals, such as platinum, white gold, and palladium, enhance the shine of any diamond, but they look particularly amazing with high-quality stones. If you want a bolder shine or have a diamond with a lower color grade, yellow gold or rose gold are great options to make a diamond look brighter.

Recommended cut grade

So what cut grade do we recommend to guarantee your diamond shines as bright as it can?

  • For round diamonds, we suggest an Excellent cut with Excellent polish and symmetry, as the investment is worth the endless sparkle of a perfect diamond.
  • For fancy shapes, still opt for an Excellent cut, but Very Good polish and symmetry will be good enough to make a lasting impression.
Inspecting Diamond Cut Quality Under Magnification

The most important step in choosing a diamond and cut quality that work for you is inspecting the diamonds yourself. If you plan on visiting a jeweler, make sure you get a chance to examine the diamond under multiple types of lighting as well as magnification. If you shop online, choose retailers like James Allen and Blue Nile that offer panoramic views of the diamond under bright lighting so you can inspect it thoroughly.

A cut above the rest

Diamond cut is a nuanced factor to consider when shopping for a new diamond. However, with a little research, you’ll be able to shop smartly.

✅Cut can affect so many facets of a diamond’s shine, and it’s truly the most important C to consider for those who want a stunning stone.

While cut is the most important C in terms of scintillation, the other three Cs are also crucial players in a diamond’s overall appeal. Take a look at our articles on clarity, color, and carat weight to determine your preferred sparkle.

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