The Diamond Pro

Diamond Cuts Guide: Overview, Grades, Quality and Price

By Michael Fried
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Bottom Line Recommendation

Cut is possibly the most important of the 4Cs. If you ignore it, you can make an enormous mistake. For example, this diamond seems like a great find, as it is 5% cheaper than this diamond. In reality, the diamond will have no brilliance and is very poor value.

If you’re buying a round diamond, limit your selections to “Excellent” cut diamonds (if graded by GIA) or “Ideal” cut diamonds (if graded by AGS). If you’re buying any other shape diamond, it’s essential that you see a high quality image of the diamond before deciding to buy as fancy shape cut quality cannot be deciphered using certificate stats alone. Because of this, we recommend you stick with Blue Nile or James Allen.

When it comes to round diamonds, despite them all being uniform in shape, the difference between a well cut diamond and a poorly cut diamond is enormous. You can have something like this ridiculously brilliant diamond that runs circles around a poor cut like this one.  Despite the second one being a higher color grade, the first one is a much prettier diamond.

As always, if you’re unsure about any aspect of the diamond buying process, please feel free to contact us with your questions.

What is a “Diamond Cut”?

Diamond Cut is how well a diamond is cut and polished, including how well-proportioned the stone is, its depth and symmetry. Diamond Cut doesn’t refer to the shape of the diamond, such as an Oval or Pear Shape. Cut quality directly impacts the diamond’s beauty and brilliance. A well cut diamond is luminous and reflects white and colored light back to your eyes. A poorly cut diamond is dull instead of brilliant. 

Differences in Diamond Cut greatly impact beauty, aesthetic appeal and the value of a diamond. It is the most important of the 4Cs.

How GIA grades Diamond Cut Quality for Round diamonds

GIA diamond cutting grades for Round diamonds range from Excellent to Poor. Diamond cut grade is based on a number of factors including symmetry, polish, brilliance and fire. For the most brilliance and beauty, only consider Round Brilliant diamonds with an Excellent cut. Ensure the symmetry and polish of the diamond are either Excellent or Very Good.

The reality is that 55% of all Round diamonds receive an excellent cut grade from the GIA. About 25-30% of these “excellent” diamonds are not recommended. Our consultants review thousands of Excellent cut diamonds and find bad specs (depth, table and angles).

That’s why it’s important to look at the diamond cut grade on the GIA certificate, but to also review the diamond closely yourself or ask an expert. You don’t want to end up paying for an Excellent diamond that’s only mediocre.

Diamond Cut Grade Chart

A professional gemologist at the GIA reviews each diamond under magnification to determine the Cut grade. Here are the GIA diamond cut grades:

ExcellentExcellent Cut Diamonds provide the highest level of fire and brilliance. Because almost all of the incoming light is reflected through the table, the diamond radiates with magnificent sparkle.
Very GoodVery Good Cut Diamonds offer exceptional brilliance and fire. A large majority of the entering light reflects through the diamond’s table. To the naked eye, Very Good diamonds provide similar sparkle to those of Excellent grade.
GoodGood Cut Diamonds showcase brilliance and sparkle, with much of the light reflecting through the table to the viewer’s eye. These diamonds provide beauty at a lower price point.
FairFair Cut Diamonds offer little brilliance, as light easily exits through the bottom and sides of the diamond. Diamonds of a Fair Cut may be a satisfactory choice for smaller carats and those acting as side stones.
PoorPoor Cut Diamonds yield nearly no sparkle, brilliance or fire. Entering light escapes from the sides and bottom of the diamond.

The AGS diamond cut grade chart also includes an Ideal grade. Cut quality is graded by the AGS as Ideal, Excellent, Very Good, Good, Fair or Poor. When looking at AGS diamonds, we recommend only considering Ideal cut diamonds for the best quality.

How Cut Grade Affects Price

Diamond cut prices are based on the precision and quality of the cut—primarily its proportions and symmetry.

If the facets (the glossy flat surfaces of a diamond) are proportional, for instance, they refract and reflect light back to the eye in tremendous fashion. Diamonds that aren’t as precisely cut have facets and pavilions that do not refract and reflect light as spectacularly.

The amount of light return and brilliance found in an exceptionally cut diamond is worth the extra diamond cut price. Without brilliance and fire, a diamond is less than radiant—no matter the Carat weight or table size.

In other words, a diamond’s Cut is the quality that most significantly impacts its beauty. That’s why the higher diamond cut prices are worth every penny—and it’s better to spend more on Cut than on Color or Clarity.

For example, Brian Gavin offers a Signature collection called Hearts & Arrows which includes some of the best Cut diamonds on the market. For instance, this diamond has tremendous brilliance at an excellent price point. It would be perfect for a 1 carat diamond engagement ring.

If you’re working within a budget, we recommend forgoing a GIA grade in Color and Clarity to ensure you’re selecting an ideal cut diamond.

Factors affecting Diamond Cut (& Price)

The most important factor in a diamond’s value and price is its Cut quality. Many elements are involved in Cut quality including its proportions, facets, finishing details and ability to reflect light. The better these characterstics are as a whole, the higher the quality of the diamond, and in return, the higher the price. While Color and Clarity play a role in a diamond’s beauty, Cut is the most critical of the 4Cs.

Here are the main factors that affect the price of a diamond:

  • Proportions (table, width, depth)
  • Symmetrical facets (the mirrors, windows and steps of a diamond)
  • Brilliance (brightness of white light reflection)
  • Fire (dispersion of colored light)
  • Scintillation (the flashes of sparkle when light moves)
  • Finishing details (permanent treatment and polishing)

Diamond Proportions

To further understand the factors impacting Diamond Cut quality, let’s examine a diamond’s proportions, primarily its table, width and depth. These elements are universally measured and are excellent indicators of a diamond’s cut quality.

Diamond Measurements

Diamond Cut Proportions directly affect a diamond’s ability to reflect light and provide brilliance. Proportions are based on the ratios between size, angle and shape of each diamond facet. Various combinations of these elements impact how the diamond will interact with light, which determines its overall beauty and lasting appeal (as well as its GIA grading).

How Light reflects through a diamond

About Diamond Table

Diamond table % is determined by dividing the width of the table (top surface area) by the width (diameter) of the diamond. For example, if the table facet is 3.5mm wide, and the diamond is 5mm wide, the table % is 70%.

If the table percentage is too large, light won’t reflect off of the diamond’s crown angles and facets. Vibrant reflections of color won’t be seen as the light will escape from the top of the diamond instead of reaching the eye.

If the table percentage is too low, light will remain trapped inside the diamond and be emitted through other parts of the diamond instead of to the eye.

The ideal table % depends heavily on the Diamond Shape. If you’re unsure of an excellent table % for your diamond, please
contact us
and we will walk you through the options and factors.

About Diamond Width

A diamond’s width is determined by measuring from one end of its girdle (the diameter at its widest point) to the other end of the girdle.

The width is most important when it comes to determining length to width ratio, which signifies how proportionate the diamond is along with its intended shape (i.e. square vs. rectangular).

Length to width ratio is measured by dividing the length of the diamond by the width. For example, if a diamond has a length of 5mm and a width of 3mm, the length to width ratio is 1.67.

About Diamond Depth

Depth % refers to the height of the diamond, from the culet to the top of the table. Depth is measured in millimeters and percentage. By dividing the depth by the width, the depth % is achieved.

As an example, if a diamond is 4mm in depth and 4.5 mm in width, the depth percentage is 88.8%.

In most cases, a lower depth % of two equal carat diamonds will appear larger due to the increased width. On the other hand, a depth % that is too low can create a darker appearance as it will not reflect light as powerfully.

What happens when a Diamond Cut is too shallow?

When a Diamond Cut is too shallow, light hits the pavillion at a low angle. The light travels through the diamond and exits through the sides, instead of reflecting through the table and to your eyes.

While shallow cut diamonds may seem large based on their table size (they are also called Spready Diamonds), the escape of light at the bottom significantly reduces the diamond’s brilliance, sparkle and fire.

What happens when a Diamond Cut is too deep?

When a diamond is cut too deep, light hits the pavilion at a sharper angle, causing it to immediately reflect to another pavilion. The light is forced to retract and pass through the bottom of the diamond. As this happens, light is dulled and the diamond becomes less vibrant and radiant.

A Diamond Cut that is too deep also tends to look smaller than those of an ideal cut.

What is the best cut for a Diamond?

Simply put, a well cut diamond maximizes the light that strikes each pavilion. Instead of escaping through other parts of the diamond, light reflects back through the crown and table.

When it comes to determining the highest grade possible, GIA uses the term “excellent” while AGS (the inventory of the cut grade) uses the word “ideal.” These cuts are well proportioned with optimal facet angles, allowing the brilliance and fire to pass through the table for all to see.

For these reasons, excellent cuts are more valuable and more luminous. When buyers have a budget, we often advise choosing a smaller, well cut diamond as opposed to a larger carat that is poorly cut.

If you’re unsure of an ideal cut for your diamond, speak to an expert to walk you through the process.

Symmetrical facets

The facets of a diamond are the tiny mirrors that reflect light back to your eyes. Facets surround the diamond’s table. There are facets above the girdle and below the girdle. The pavilion (the part of the diamond below the girdle that reaches to the culet) is also made up of facets. A Round Brilliant diamond is cut with 58 facets total.

The size, placement and symmetry of the facets impact how well the diamond refracts and reflects light. A diamond with unproportioned facets, too many facets or not enough facets, can cause a less than ideal diamond. 

Brilliance

A diamond’s brilliance is the brightness of the white light reflection. When looking at a diamond face-up under light, it should reflect an abundance of white light. A diamond that’s not symmetrical, is cut too deep or too shallow, for example, looks dull instead of brilliant.  

Fire

A diamond’s fire is the amount of colored light that reflects off of the table and facets. Diamonds that are well cut not only have brillance but fire too. When looking at the diamond face-up under light—especially daylight—you should see colored light bouncing off of the diamond. If the diamond doesn’t exhibit colored light reflection, the diamond has a low amount of fire.

Scintillation

Scintillation of a diamond refers to the flashes of sparkle when light moves on the diamond’s table and facets. The scattering of light resembles a sparkle and is caused by the light and dark areas on the diamond’s surface.  A diamond with a large amount of scintillation is more desireable. A diamond without much scintillation can appear dull. 

Finishing details

The finishing details are the craftmanship of the diamond and include its permanent treatment and polishing. The polish of a diamond refers to the condition and quality of the facet surfaces. A diamond that is polished well creates a clear mirror for light to reflect off of. A diamond with a poor polish job looks dull because the facets don’t reflect light as vividly. 

Factors for Determining Diamond Cut Quality

Because Diamond Cut is an enormous element in determining the beauty and brilliance of any diamond, there are some complexities. Many factors play a role in how a diamond’s cut quality is determined.

The main factors impacting Diamond Cut Quality are:

  • Proportions: the ratios and sizes of the diamond’s depth, width and table
  • Symmetry: precision of the facets, mirrors, windows and steps
  • Polish: the shine and glow of the diamond surface

When you’re looking to see how well cut a diamond is, take note of how its facets and angles reflect light. Specifically, note how bright and sparkly the light return is when placed under a normal lamp.

You’ll want to gauge the diamond’s fire (the rainbow light of reflection) and its brilliance (colorless light and sparkle of the diamond). Be sure to also watch for any dark spots within the piece.

When a diamond is poorly cut (even if it has a high Color or Clarity grade), light will not reflect as well back to your eyes, making it a duller, more lifeless diamond.

Be sure to review the GIA cut grade on a diamond’s report, which will include ratings of Poor, Good, Very Good or Excellent.

What’s the difference between Diamond Cut and Diamond Shape?

The terms Diamond Cut and Diamond Shape have distinct meanings.

Diamond Shape describes the outline or figure of the diamond. For example, Pear Shaped and Round Brilliant refer to the shape appearance of the diamond.

Cut refers to the facets, symmetry, dimensions and reflective qualities of the diamond. A Heart Shaped Diamond, for instance, may be cut shallow or deep, dull or brilliant. The Heart Shape remains, while the Cut may differ significantly. The finer the cut, the greater the brilliance and fire of the diamond.

Our Recommendations For Buying The Right Diamond

When it comes to selecting an ideal diamond, we recommend a quality Diamond Cut over anything else. For GIA Certified Diamonds, we recommend choosing an Excellent cut grade. For AGS Certified Diamonds, choose an Ideal cut. When we search for a diamond, we filter more heavily on Cut. You can see our parameters by looking at this James Allen diamond search.

For Maximum Brilliance: Consider a Brian Gavin Signature cut. Brian is a leading industry expert in the field of cut optimization. His Signature cuts are on par with the famed Hearts on Fire brand—only far cheaper.

For Round Brilliant Cut Diamonds, don’t give any credence to an online vendor’s cut grade. Only focus on the GIA or AGS cut grade on the certificate.

In addition to reviewing a GIA or other grading report, be sure to look at the diamond yourself or have an expert assist you. Most importantly, ensure the diamond is appealing to you and your personal style and desires.

Our primary focus is making sure your diamond search is easy, simple and accurate. We want you to find the highest quality diamond while staying within your budget.

If you’d like assistance with finding and selecting a diamond, we’ll be happy to filter through the cuts and make recommendations for you.

About the author
Mike learned the diamond business from the ground-up at Leo Schachter Diamonds - one of the world's top diamond manufacturers. He has been recognized as a diamond industry expert by Time, PeopleMoney, The Daily Mirror, NerdWallet, The Times Herald, Yahoo Finance Australia, The Art of Charm, The Washington Diplomat, The Next Web, and more. See more
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