Understanding Diamond Cut: Everything You Need to Know

The Cut of a diamond may be the most important factor in how beautiful it is.

Clarity is important. Color is important. The Carat weight of a diamond is important.

And yet Cut is the queen of the famous 4 C’s of diamonds.

Why is that?

  • It’s because Cut greatly affects the beauty, appearance, and the value of a diamond.
  • It also determines the two most pleasing aspects of diamonds — fire and brilliance.

You could have a diamond of flawless Clarity, but if it’s cut poorly by the diamond cutter, it will appear dull and lifeless.

Not good.

As I’ve written elsewhere, some diamonds of objectively poor clarity can actually reach the level of “eye clear.” So you don’t need a high level of objective Clarity for a diamond to appear beautiful — and to sell at a welcome discount.

But there’s no hiding poor Cut. Poor Cut always results in a dull diamond of very little value.

  • That’s why Cut is so important when you’re shopping for a diamond engagement ring.
  • That’s why it’s so important to understand the basics of Cut.
  • The basics aren’t hard to understand.
  • I will explain the basics of cut, in plain English, right here in this short article.

What Is Diamond Cut? Hint: It’s Not the Shape

Do you wonder what Cut is, exactly? It’s not the shape of a diamond.

Cut refers to the mathematical dimensions, angles, and percentages of the diamond.

“Cut” is not Shape. Shape is Shape. Here are the ten most common shapes of diamonds.

  • Round
  • Princess
  • Pear Cushion
  • Heart
  • Asscher
  • Oval
  • Emerald
  • Marquise
  • Radiant

Cut is different from shape.

Cut refers to the angles and measurements of the facets, and to the symmetry and reflective qualities of the diamond.

Imagine a drawing. It’s a line drawing. Just lots of lines and angles. Just a 2D drawing. Any number of lines. Any angles you like.

An infinite number of possibilities, right?

The concept of diamond “Cut” is like that, only in 3D.

Just as with a 2D line drawing, in a 3D diamond cut, a diamond cutter can find a virtually infinite number of possibilities. It could be sharper here, less sharp there. All the lines can be “drawn” (cut) in virtually any available angle.

The skill and creativity of the diamond cutter is one of the two most important factors in how well a rough diamond is cut into a gemstone worthy of a diamond engagement ring.

The skill of the diamond cutter is only one factor.

The other factor is the individual qualities of the rough diamond itself.

Every diamond is different. Every diamond has a combination of qualities that both enable and limit its possibilities, even in the hands of the best diamond cutters in the world. Inclusions (flaws) in the diamond will limit some choices.

So what?

The better the Cut, the more brilliance and fire will be in the diamond.

That’s the main thing with diamonds. Fire. Brilliance. Sparkle. It’s determined by the angles. It’s determined by the Cut.

What You Should Understand About Cut

If you’re new to shopping for diamonds, it probably means you’re new to looking at them. New to appreciating them.

When you were new to coffee (can you remember?), you may have thought, “So what, it’s coffee. Yeah it can be fresh or stale.”

Maybe McDonald’s coffee tasted, to your inexperienced palate, like single-origin Ethiopia Yirgacheffe roasted by your local coffee shop.

Or maybe, when you were, ahem, 21, and first sampled beer, Budweiser tasted about the same to you as a craft lager.

But you quickly learned the difference. About as quickly as it took you to compare and contrast a few brews.

Or maybe (final example, promise), you didn’t really know the difference between a Walmart kids’ bike and real bicycle until you compared and contrasted.

Stunning, right? The first time you’re on a good bicycle. They’re both bicycles. Who would have guessed, but one is worlds better.

That’s where you might be in your diamond journey, if you’re just starting out.

You may not have experienced the difference in brilliance and fire among individual diamonds. But you will now, immediately.

Fire and Brilliance

The vast differences in sparkle, and fire, and brilliance of diamonds is real. It’s moving.

And when you begin to see the differences — you can use the incredible imaging at James Allen or Blue Nile — you’ll really get it, the way you really got the differences among coffees, or beers, or bicycles.

And look at them in person, too. Virtually any woman — or man — you know personally who is wearing a diamond engagement ring will be very happy to show you, and let you admire it.

And you’ll get it as rapidly as you did with beer or coffee or bicycles. Diamonds are just more expensive than bicycles. They’re not more complicated. 

In fact, in many ways, they couldn’t be more elegantly simple. Almost the only question about a diamond is:

How much fire and brilliance does it have?

And what determines that all-important quality?


How Does Cut Determine the Fire and Brilliance of a Diamond?

It’s physics. It has to do with quite detailed and scientific qualities of light and diamonds. 

And being physics, it’s complicated.

I’m not going to give you a physics lesson, not least because I’m not a physics professor.

But unlike some professors, I’ll answer the question in plain English that you’ll understand instantly.

A good Cut causes light to escapefrom the top of the diamond. (Called the “table” and the “crown” in diamond cut jargon.) 

Cut Consists of These Three Things

  1. Proportion (See the illustrations below, and trust me you’ll get it at a glance.)
  2. Symmetry (Again, see the illustrations below.)
  3. Polish (The surfaces — known as “facets” — of the diamond are well polished so that all the light can escape and not be held in by a less than transparent surface.)

What Is the “Fire and Brilliance” as Determined by the Cut?

It’s when the geometry of the diamond causes light to escape from the table and the crown of the diamond. (See the illustration above.)

Not the sides (which are called the “girdle”.)

Not the underside of the diamond (the “pavilion”).

When light is directed to escape from the table and crown, you know the diamond has a top-quality Cut. You can see that in how well the diamond sparkles fire at you.

What Are the Five GIA Grades of Diamond Cut?

Excellent Virtually all the light exits through the table. Maximum fire and brilliance.
Very Good Most of the light exits through the table. Most people who aren’t trained for grading diamonds can’t tell much difference between Very Good and Excellent.
Good Much of the light exits through the table. These diamonds are still beautiful. They give a lot of pleasure. And they can be a good value because they’re not as expensive as Very Good or Excellent.
Fair Much of the light exits through the pavilion and culet of the diamond, depending on the shape). Not great fire and brilliance.
Poor Almost all the light exits through the pavilion and culet. Not a great experience at all. Very minimal fire and brilliance.

What Is the “Ideal Cut” I Sometimes See Mentioned?

“Ideal” is the AGS (American Gemological Society) top grade of diamond cut. AGS has proprietary descriptors for their diamond cut grades. The plain English version, in my view, is this:

AGS grades diamonds on a scale of 0 (best) to 10 (worst).

The AGS top grade of 0 is called an “Ideal” cut.

Why You Should Trust Only a Certificate

We’ve emphasized this in many articles. And again we emphasize: trust only a certificate from GIA or AGS, when you’re told what a diamond’s cut is.

A reputable seller always provides a GIA or AGS certificate for a diamond. And yes, before you buy it, you can see it. It’s linked right there on the product page, for example, at James Allen.

james allen certificate

Just as you wouldn’t buy a home without a deed, or a thoroughbred horse without a pedigree, never consider buying a diamond for an engagement ring unless it has a certificate.

Among other important grades and specs on the certificate, you’ll find the Cut grade.

What Cut of Diamond Should You Buy for an Engagement Ring?

The best cut you can afford.

Don’t buy “Fair” or “Poor”.

Go for “Good”, “Very Good,” or “Excellent”.

We advise people to prioritize cut over size and clarity and color.

The reason is simple: even a small diamond, of “eye clear” clarity, can have stunning fire and brilliance.

Everything depends on you and your beloved, of course. You wouldn’t let a coffee connoisseur tell you what kind of coffee you like.

But assuming that you do love the fire and brilliance of diamonds as much as most people do, prioritizing Cut will get you more of what you want.

The masses, bless their hearts, ask and exclaim only about the carat weight, as if size were the most important quality of a diamond.

But now you know better.

Diamonds and Light: The Most Eternal Combination

A diamond is forever.

Something else is also forever. It’s the most incomprehensibly fast, mysterious, wave and particle dilemma, a thing like gravity, which occupies the best minds of our species: light.

The diamonds that give you back the most beautiful qualities of light are not necessarily the largest diamonds. Or the clearest, or the most absent of color (although clarity and lack of color are important).

The diamonds that give you back the light are the diamonds with the most perfect cut.

You can adjust for cost by sizing down in carat weight. Or you can opting for eye clear diamonds. You can spend your money where it has the most effect: by choosing

  • Ideal (AGS) or Excellent (GIA)
  • Very Good (GIA)
  • Good (GIA)

Is an AGS Ideal Cut Better Than a GIA Excellent Cut?

These are simply two different grading scales. The best diamond in the world would be graded by the AGS as Ideal and by the GIA as Excellent. Same diamond. Same quality. Two different names for it.

Every diamond is different. The grades are ranges of quality.

How to Save Money in Order to Get the Best Diamond Cut Possible

A wonderful thing for anyone shopping for diamonds these days (and it’s only been very recently that it’s possible) is the Internet.

You can see more diamonds in 10 minutes than your grandparents could see in 10 years.

Also, you can know the price of every single one of them. Instantly.

You have global knowledge of the retail diamond market. It’s all in the databases of highly reputable retailers such as James Allen, Blue Nile, Brian Gavin, and others.

How to Adjust Diamond Selections to Afford the Best Cut

  1. Prioritize cut, if you, like most people, appreciate diamonds most for their qualities of brilliance and fire.
  2. Go James Allen’s or Blue Nile’s diamonds sections.
  3. Adjust with the filter sliders to select diamonds from their vast inventories for Cut, Carats, Color grade, and Clarity.

In general terms (every diamond is unique and priced individually, so it’s not like selecting or deselecting options on a luxury car), here’s how you can adjust your selections in order to advance a grade in Cut, while keeping the same Carat weight:

  1. Go down one GIA grade in Clarity.
  2. And also go down one GIA grade in Color.

Even more important: Think outside of the box of a single buying experience.

Where can you trim costs in your budget elsewhere? Money has that wonderfully useful quality of being fungible.

Money you save on coffee, or by not ordering drinks, is available for spending on a better Cut of diamond.

Money that you make with a side hustle is available for spending on a better Cut of diamond.

Final Thoughts

Now you get it. I hope that, even if you had no idea what Cut meant, in terms of a diamond, that you now know that you get it.

You now know that Cut is the geometry of the diamond that causes light to escape from the table and the crown, not from the pavilion or the culet. (That’s pronounced in English as cue-let. No need to Frenchify it, every English speaker just says cue-let. You’re welcome.)

Questions About Cut?

If you have any questions, contact us.

We love helping first time buyers of engagement rings get the ring they want, at a price they can afford, without making mistakes or getting ripped off.

We stand ready to help, so don’t hesitate.