Diamond Cut Definitive Guide: Cut & Brilliance Harmony

Diamond Cut Definitive Guide - Cut & Brilliance Harmony

When you put your mind to purchasing a diamond, take a loupe and check the cut and clarity. After that, try to take the gem outside (away from the artificial lights) and -if possible- to natural sunlight, also in the shade; to see its true color and sparkle! 

As we keep reminding our readers in this blog, if you happen to have a low budget and you decide to choose a higher carat, expect a poorer cut, clarity, and color. Its sparkle and scintillation won’t be the best either!

It’s always a wiser choice to get a smaller carat and a brilliantly cut beautiful stone than a lump of dullness!

To demonstrate, look at these two diamonds from Blue Nile, both are identical in terms of color, carat, and clarity, however, the one to the left has an excellent cut, while the one to the right is just good (which is not good at all!):

Good vs Excellent cut BlueNile

It would be interesting to know that both diamonds hold “almost” the exact characteristics, except for the cut.

You can clearly note the huge impact of the cut on each of the diamonds! Although the price is around $500 between both, it’s absolutely worth every penny (and as a matter of fact, it will be a waste of money to get the “not” good one!).

What is diamond cut though? And what is its importance exactly? And how does it fit to the whole picture of your choice of a perfect diamond?

Unlike local jewelry shops, where the jeweler/salesperson tries to convince you to get a higher color like D color grade, or carat in order to have a better diamond (AKA: a more sparkling diamond), diamonds experts & professionals will always tell you the truth:

Whatever budget you have, always get settled with an Ideal/Excellent cut at least, then (and ONLY then) start looking for other factors!

Back to our topic “What is diamond cut”. Being the most important factor among diamond characteristics (including the 4Cs), diamond cut is the most frequent specification you’ll be hearing about while searching for your perfect gem!

Why Cut is the most controversial factor when discussing diamonds? What are the grades when it comes to diamond cut chart? How does each grade affect diamond light reflection?

This post will have all the answers for that, and also all what you need to know about diamond cut, and the cut chart as well!

We will also take a quick look at the most popular diamond shapes since we already have a separate detailed article for diamond shapes.

What is Diamond Cut?

Diamond cut refers to the proportions of the parts of the diamond, and how well the diamond facets reflects light when exposed to direct light.

Diamond cut is considered to be the most important job of artists and workmen who craft the diamond to make it as symmetric as possible, as well as proportional & polished well to reflect the maximum amount of light.

You surely know that sparkle you see when looking at a diamond! Ever wondered why some diamonds sparkle more than others (you might also see this referred to as Diamond Brilliance)?

Another example for diamonds with different cut, but now from James Allen with better imaging technologies:

Here is a diamond that’s 1 Carat, H Color, and VS2 Clarity. A general look at the diamond characteristics might tell you that it’s a good one, but actually, it’s not! Take a magnified look using the 360 degrees feature and a 40x magnification by James Allen, is the stone’s brilliance any good?

Now compare it to this one, a very similar diamond in terms of clarity, carat, and color, but way different in light reflection and brilliance, isn’t it?

That’s exactly the difference between a good cut diamond, and an ideal (Excellent) cut diamond! And this is what we’re going to cover in this blog post! 

Let’s now dig a bit deeper to understand the correlation between Cut and Brilliance!

How Diamond Cut Affects Brilliance?

As defined above, Diamond cut demonstrates how the diamond was made (or how it got cut/shaped), it also reflects how diamond facets are proportioned against each other and how diamond dimensions are well-proportioned, the surface is polished, as well as the diamond’s depth and symmetry! 

Diamond Sparkle James Allen

All of these combined (and not a single factor excluded) determine the amount of light the stone is able to reflect! The higher the reflection, the better the performance, and the more need for a higher cut grade!

When you examine the diamond’s interaction with light, you’ll notice that this light is the reflection that goes off the diamond’s table facet mainly, and then off the crown facets. It’s worth mentioning that the more symmetric they are (the crown facets), the higher their ability is to reflect light.

Here is an image that shows different parts of the diamond in order for this information to sink in:

Diamond Anatomy


Most often than not (actually 9 times out of 10) a diamond with bland look, low light reflection definitely has a bad cut.

Did you know that of all the 4Cs, a diamond cut is the one that has the greatest effect on the look of the diamond to the naked eye, wonder how and why?

The drop from VS1 to SI1 clarity or an F to H color (both of a two-grade difference) is hardly noticeable to naked eye under regualr light.

However, a drop from “Ideal” to “Good” cut grade will often be noticeable to the naked eye because it will lack that sparkle that one would expect.

Fact: It has been proven by Gem professionals that no two diamond stones are identical! You can never find two stones that have the same characteristics although they might actually look exactly the same under a layman’s vision.

How Diamond Cut Affects Light Reflection?

Physics 101

When light bounces off a surface, it’s called “reflection”. And when the surface is smooth/polished, the light reflects at the same angle that it hit the surface at!


Long story short, when the light hits a diamond, it bounces back up immediately; which gives it that instant scintillation and shine! However, this is not the only reason! 

Multiple numbers of refractions result in the diamond sparkling way more than other substances.

An article written by lumen Learning suggests that light cannot easily escape a diamond and that the facets are placed in a way that light can exit the gem only in particular ways; thus concentrating the light and making the diamond sparkle.

Take a look at the image below and notice how when a diamond is Cut to excellent & v.good proportions, light is refracted from one facet to another, then dispersed through the top of the diamond.

When a diamond is cut too deep, some light escapes through the opposite side of the diamond. On the other hand, if the diamond’s cut is too shallow, the light will escape through the bottom of the stone before it even has the chance to be reflected.

Note: For maximum brilliance, the facets must be placed with precise symmetry!

Diamond Cut Light Reflection

Image courtesy of Taylor & Hart

The diamond cut is basically made up of a set of proportions (including the diamond’s diameter, table, and crown).

It’s important to mention here that although the image here groups Excellent & V.Good cuts together, truth is that both grades aren’t the same of course, why would GIA separated them if their ability to reflect light is the same?

They are grouped just for the sake of illustration how diamond proportions loook like in different cuts, since both Excellent & V.Good have “almost” similar look (in terms of L/W ratio).

In total there are 7 measurements that contribute to the Cut, but 2 stand out as the most important: Table and Depth.

The Table is the large polished part of the diamond that faces up, while the depth is the total measurement of the diamond (from top to bottom)

What is Diamond Cut Grading Chart?

Similar to the color & clarity, diamond cut has a chart that exists to help define and categorize diamond grades.

There are different grading systems to determine a diamond cut, however, the most common and agreed-upon one is the cut chart created by GIA, since it’s known to be the best diamond certification lab.

GIA Cut Grading Chart subdivides diamond cut into 5 grades:

Poor, Fair, Good, Very Good, and Excellent (AKA Ideal cut).

You might see a grade named Super Ideal at some stores like James Allen or Blue Nile, and don’t worry, we will see more about this grade shortly, but it’s worth mentioning that it’s not a grade defined by GIA.

Let’s talk a deeper look on each of these 6 grades:

JamesAllen Promo

1) Poor

These are the diamonds that reflect no light at all! Despite the fact that the probability of the existence of these types is uncertain, absolutely all reputable online diamond stores (like JamesAllen and Blue Nile) do NOT sell any poor cut diamonds!

Also, read JamesAllen Vs. Blue Nile Detailed Review & Unbiased Comparison.

2) Fair

It’s not like they are ‘bad diamonds’, still, they are not well-cut diamonds and this definitely affects their quality as they reflect a very small percentage of the light passing in the gem! 

Tip: Even if you find yourself on a very low budget and you came across this grade, we would never recommend you get it! Anyhow, if you were on a very tight budget, think about getting a lab-created diamond instead, just NEVER ever get a fair-cut diamond.

Since it’s very unlikely to find a fair-cut diamond in reputable online stores, watch out for the local jewelry stores and always make sure to see & verify diamond certificates before proceeding with the buying decisions!

3) Good

These diamonds are partially well-cut (based on the quality of sparkle that they give). They are cut in a way that they don’t lose their beauty or quality. And although they don’t reflect all the light penetrating them, they are still considered not that cheap!

You can easily find good cut diamonds on all online merchants, but if you want our professional opinion, we wouldn’t recommend this grade, a good grade is NOT that good when it comes to diamonds.

Check out this: Diamond 4Cs and Order of Importance

4) Very Good

These gems’ value is high in the market; as these diamonds exhibit a higher cut and quality than the Good grade and reflect a higher percentage of light; hence they sparkle more than the Good grade!

We consider this grade to be, how can we say that, the most budget-friendly one of all! (it’s still expensive though). While we always recommend trying to get excellent (ideal) even for lower carats, a lot of people go to v.good because it’s cheaper.

Always try to invest to get this grade (at least) more than any other factor.

5) Ideal (Excellent)

If you’re asking: What is the Best Diamond Cut out there?

The Ideal cut, no question! 

Always seek an ideal cut even if it means getting a lower carat! 

Ideal & Excellent terms are used interchangeably in diamond online stores & merchants, but in terms of diamond certificates, AGS considers Ideal as the grade above excellent (which we will see shortly), GIA however, doesn’t define any grade higher than Excellent.

Diamonds of this grade have a combined force of brilliance and fire; they sparkle and shine effortlessly, as well as reflecting most of the light that passes through the crown facet.

Symmetry and proportions (even Hearts & Arrows) of this grade are set to the most ideal figures, leaving a very small difference for the next “unofficial” grade when these metrics have reached the maximum.

Here are images for two diamonds we found on Blue Nile, both have almost identical characteristics, except for the cut: the left is very good (link) and the one to the right is excellent (link), you can clearly spot the difference between these two grades:

1carat G VS2 V.Good Cut Blue Nile

Only 3-5% only of global diamonds make it to this grade which makes it pretty understandable why they are this expensive.

5.A) Super Ideal (Hearts & Arrows)

As you noticed, we didn’t consider this grade as number 6, because simply it’s not an industry standard, but it’s worth to be distinguished from Ideal.

When Scintillation, Fire, and Brilliance mix altogether, the result is a “Super Ideal” gorgeous diamond! These diamonds are absolutely the pride of every cutter and jeweler.

They are superbly cut and rank the highest in the diamond grading system.

Different online vendors refer to such grades with their own trademarked terms, so, for example, JamesAllen offers this grade as True Hearts™, while Blue Nile names them Astor By Blue Nile, and you can see A CUT ABOVE grade on Whiteflash.

Blue Nile Ring

With these types of diamonds, light reflection is out of this world (in most cases! That’s why we encourage you to read links above for True Hearts & Astor).

Even so, just keep in mind that this grade is not defined by GIA, so don’t go around expecting to see this grade on any GIA certificate (for a TrueHearts diamond for example)!

Astor as well is not graded accordingly by GIA, the only exception here is for A CUT ABOVE, where it’s clearly indicated on AGS certificate (but not GIA).

What Makes a Diamond Cut Grade? Types of Diamond Reflection

What determines the quality of a diamond Cut and decides which grade it should have on a cut chart?

In other words, what exactly makes an artisan a pro in creating the perfect diamond cut?

As it’s been clearly demonstrated before, the “Cut” is the most influencing factor in light reflection through a diamond.

And when a diamond is cut to ideal proportions, the light reflection is pretty well, on the contrary to a poor cut; which will result in light going through the diamond and exiting from the other sides.

The quality of the cut of a diamond is determined by the following three types of light reflection:

1) Brilliance

This is actually the most common type among light reflection methods. It’s the white light that we see when we look at a diamond, it’s the light that passes through to the diamond and then reflects back off the surface and into our eyes.

To illustrate more accurately, light doesn’t go from the top, goes to a facet, then to the opposite one, and reflects back, this is not how it really happens! Because if that was the case, the reflected light will be absolutely minimal.

When light enters a diamond and clashes into one of the facets, it keeps bouncing off between mirror-like facets endlessly and this is what really causes a great sparkle.

Some very good/ideal Cut diamonds reflect all the light as white color, the lights get into the diamond white and leave white.

On the other hand, due to a less professional diamond cut, the light enters as white and reflects as rainbow, this image shows both cases (image taken from Whiteflash, house of A CUT ABOVE diamonds):

Diamond brilliance white

2) Fire

This is a myriad of colors that reflects when light penetrates the crown of the diamond. The light internally bounces back and forth in the diamond and flashes the eyes in a myriad of colors.

Do you see the rainbow that reflects back from a diamond? This is what Dispersion or Fire represents! It’s the rainbow of colors that reflects back to your eye when you look at a diamond. 

The Light; similar to the first left diamond in the last image, enters through the top and breaks down into a rainbow of spectral colors, then reflects in the interior of the gem by bouncing off the mirror-like facets.

Therefore, when it leaves the diamond (through the crown), it doesn’t get mixed with the entering light, rather, it appears as an independent beam until it reaches the eye in flashes of colors.

Diamond Rainbow reflection

3) Scintillation

Do you notice when you look at a moving diamond how light reflects through that? This is exactly what is described as scintillation, it’s basically the light symphony playing in front of you when you move the diamond in different angles under the light and it’s demonstrated by the sparkles on the diamond’s surface.

You can see it in the same image we used to demonstrate brilliance, the only difference with scintillation is that scintillation appears when you move the diamond.

As you see in this image, when such a diamond is moved around the light, you can see different angles of reflecting color, a very good diamond cut will retain a good reflecting light when this happens.

Diamond brilliance white

The 60/60 Diamond Cut Rule of Thumb

Now that we’re clear on the definition of both depth and table facets we saw above, we feel it’s time to introduce percentages!

The Table percentage is calculated by dividing two numbers: the width of the table by the overall width of the gem, whereas, the depth percentage is the stone’s depth (AKA height) divided by the overall width of the stone.

Here is again the diamonds parts/anatomy so you get a better idea how table & depth percentages are calculated and what they mean:

Diamond Anatomy

The most basic rule of thumb when looking for a round diamond is the “60/60” rule. What this rule states -it’s really more of a general guideline than a rule- is that you should look for a diamond with a table of 60% and a depth of 60%.

Before you take this rule for granted, we encourage you to read more about the Ideal Table & Depth percentages here.

Each diamond shape has its own proportions that are somehow considered best, however, round diamonds are the only ones that are defined on the diamond certification.

Whiteflash A-CUT-ABOVE-Hearts-and-Arrows-Diamonds

Unlike the 60/60 rule of thumb, the GIA and the AGS diamond cut grading systems take into account the total proportions of the diamond.

Both labs might be giving a diamond an Ideal grade even if one of its parameters is slightly higher (or lower as a matter of fact) than what would be considered Ideal. (AGS doesn’t even give a 60/60 diamond its highest grade).

Nowadays, both AGS and GIA allow for mixing it up a little (more than they used to) and rely on actual return of light measurements rather than rigid numbers.

While we often recommend going with the lowest eye-clean diamond Clarity like an SI1 (or lower if that’s what you’re comfortable with), and on Color, we don’t recommend exceeding G in all cases, you might hear an advice to get a color from colorless group (like D, E, or F color grade), this is far from the truth even if you want to get a colorless diamond, because what the eye see is different from what GIA gemologist can see.

In cut, we’re changing direction here on the Cut!

When it comes to cut we urge you to spend more for higher quality and go for the highest you can possibly afford!

Diamond Cut Vs. Diamond Shapes: What’s the Difference?

Ever wondered what’s the difference between diamond shapes & diamond cuts? You’re not alone.

A common misconception about diamond cut would be that most people refer to diamond shapes as cuts where they’re not, diamond cut is more about the symmetry, proportioning, and polish of a diamond.

Where diamond shape is as it implies, the shape (that you can tell when you look at the diamond) of a diamond, whether it’s a Round, Princess, or other shapes as we will see now.

Here, we take a quick overview of the most common diamond shapes, however, if you want the full exclusive review, feel free to read Diamond Cut vs. Diamond Shape & The Most Popular Shapes.

Popular Diamond Shapes

In the 1400s, diamonds gained popularity being used as jewelry ornaments. During that time various diamond cuts and diamond shapes were developed.

In 1919, Marcel Tolkowsky invented the Ideal Cut diamond, which quickly became recognized as the standard in round diamonds and the basic shape to be used in diamond engagement rings!

Below is a quick brief review of the most popular diamond shapes used today:

1) Round Shape Diamonds

Round diamonds are by far the most popular diamond shapes. They’re considered the norm in the classic engagement ring: a round, solitaire diamond set either in yellow gold or platinum.


Almost all the shapes other than the round shape are called fancy shapes. The most popular round cut is the Ideal cut diamond which has 58 facets.

Shop for Round Shape Diamonds on James Allen 

2) Princess Shape Diamonds

To get into the fancy diamonds topic, we would definitely start with Princess-cut diamonds.

These are considered the most popular of all fancy-shaped diamonds. Princess-cut diamonds are relatively new with an oblong shape; usually a square or almost square but with a modified brilliant cut arrangement of facets instead of a step cut.


Most square or rectangular cuts however don’t live up to the level of the sparkle of the round brilliant, the princess cut diamonds though, are designed to obtain the maximum brilliance from a square cut.

Princess shape (along with round and cushion) can be cut to a perfect proportion that’s even more than excellent, which is called “Heart & Arrows” or Super Ideal.

Some vendors (as we saw above) have a separate premium collection for those, we came across some like True Hearts™ by JamesAllen, and A CUT ABOVE® by Whiteflash.

Shop for Princess Shape A CUT ABOVE® Diamonds on Whiteflash

3) Pear Shape Diamonds

Pear-shaped diamonds are deemed a hybrid cut; combining the best of the oval and the marquise and as the name insinuates, they’re shaped like a teardrop.


Pear-shaped diamonds also complement a hand with small or average-length fingers. It works exceptionally well in pendants or earrings. 

Shop for Pear Shape Diamonds on Blue Nile

4) Marquise Shape Diamonds

Marquise diamonds have an elongated shape with pointed ends supposedly inspired by the smile of the Marquise de Pompadour and commissioned by the Sun King, France’s Louis XIV. It is often used as a solitaire or enhanced by smaller diamonds.


Shop for Marquise Shape Diamonds on James Allen 

5) Oval Shape Diamonds

Oval diamonds give an even, perfectly symmetrical design and it’s very popular among women with small hands or short fingers. Oval diamonds also have an elongated shape; making a woman’s finger appear longer.


Shop for Oval Shape Diamonds on James Allen

6) Radiant Shape Diamonds

Radiant cut diamonds have a square or a rectangular cut combining both the elegance of the emerald cut diamond with the brilliance of the round. Radiant cut diamonds have 70 facets to maximize the effect of their color refraction.


Shop for Radiant Shape Diamonds on James Allen

7) Heart Shape Diamonds

The most romantic shape of all (but not the best in terms of light reflection)!


Heart-shaped diamonds are basically pear-shaped diamonds with a cleft at the top. Anyhow, they can be really difficult to cut, the skill of the cutter is directly proportional to the beauty of the stone!

Shop for Heart Shape Diamonds on James Allen

8) Trillion Shape Diamonds

The trillion cut was developed in the late seventies. The trillion cut is an adaptation of the radiant cut with a final shape of a triangle with equilateral sides. It is a mixture cut of the step cut and the brilliant-cut diamond.

Trillion Shape Diamond

You won’t find trillion shape in common stores like James Allen or Blue Nile, since this shape is not recommended in engagement rings, but might fit well in three-stone diamonds rings.

9) Asscher Shape Diamonds

These were developed in 1902 by the Asscher Brothers of Holland. The Asscher cut is a stepped square cut, often called the “square emerald cut” and like an emerald cut, it has cropped corners. Asscher cut diamonds have gained increasing popularity only recently. 


Shop for Asscher Shape Diamonds on James Allen

10) Cushion Shape Diamonds

The cushion cut diamond is an antique style of cut. Sometimes referred to as a “pillow cut”, the cushion cut has an open culet (the bottom of the diamond) and a rectangular to a square shape with rounded corners.


The beauty of a cushion cut is the depth of the diamond. In the past, most high-quality cushion-cut diamonds were found only on the antique and estate markets, today cutters are once again (fortunately) cutting these gorgeous stones. 

Shop for Cushion Shape Diamonds on James Allen

11) Emerald Shape Diamonds

Emerald cut diamonds have a rectangular shape with cut corners. It is known as a step cut because of its broad, flat planes resembling steps on a staircase.


Inclusions and inferior color are more pronounced in emerald cut diamonds, therefore, you need to pay close attention to clarity as well as color grading.

Shop for Emerald Shape diamonds on James Allen

Summary: Final Words on Diamond Cut

Diamond-Cut is the single most important parameter that affects how your diamond looks to the naked eye. In a nutshell, here is what we’ve covered in this post:

  • Always try to get an Excellent cut no matter what budget you have, if you insist, don’t ever go lower than “Very Good. Unlike some minor upgrades (diamond color for example) going from Very Good to Excellent will offer a noticeable change (and price as well).
  • Vendors will often push for AGS Triple Zero or Triple Excellent grading from GIA.  In almost all cases this is overkill and will not offer a noticeable improvement over AGS Very Good grading. In keeping with our philosophy of paying for what you can see, we don’t recommend upgrading to the Triple Zero.
  • Beware the independent diamond cut evaluation of online vendors for round diamonds,  we have seen some online vendors listing diamonds as Ideal but when checking the actual GIA or AGS certificate found that in fact, they were not Ideal.
  • We always recommend getting your diamond from one of the reputable online stores for many reasons, like James Allen or Blue Nile.

Still not sure where to buy your diamond?

We always recommend shopping diamonds online and created a Full guide to shop diamonds like a Pro.
Among online retailers, here are our favorite stores click their logo to visit store

  1. James Allen:

    Our favorite online store, best diamond imaging technology available today, comes with the largest collection with more than half a million loose diamonds.

    Latest JA Logo

  2. Blue Nile:

    Widest collection of loose diamonds of all sizes, great imaging technology for most of their inventory (hundreds of thousands of diamonds), great customer support.

    Blue Nile Latest Logo

  3. Whiteflash:

    Home Of A CUT ABOVE® Super Ideal Diamonds, they stand out from the crowd by offering premium diamonds cuts, tailored to those who love the details, at great prices too.

    WF logo black

Scroll to Top