Why a Diamond's Cut Matters So Much

Author Long's Diamond Team
Date Feb 15, 2021

Why a Diamond's Cut Matters So Much

In the world of diamonds, the diamond's cut refers to how the facets and angles of a diamond work together to reflect light. Cut has the single biggest impact on the sparkle, brightness and the beauty of a diamond.

Here’s why: imagine trying to light up a room using just a flashlight and some mirrors... if you line up the mirrors properly, you can illuminate the whole room. If the mirrors aren’t aligned and light bounces in the wrong direction, you still have a pretty dark room.

A diamond works the same way. A well cut diamond is desirable and valuable when it has that distinctive and tremendous light return, aka sparkle and fire. In contrast, a poorly or moderately cut diamond doesn’t reflect much light back towards your eyes. So a poorly cut diamond appears flat, lifeless, dull and apparently dirty even when it is perfectly clean.

So What Determines Cut? The Cutter Does.

Only Mother Nature determines the color and the clarity of every diamond. Man can’t alter those naturally. So what determines cut? We do - or more specifically the diamond cutter does - when polishing a stone. He can either maximize its size (i.e. the biggest carat weight) or cut it to maximize brilliance (the best cut). It’s a trade-off and here’s why:

Imagine a lumpy, rough piece of diamond that comes out of the ground. Now the cutters start to polish away the material and carve away smooth facets to create a finished diamond. If a cutter wants to maximize weight, he’ll polish away as little as possible from that rough EVEN IF the final product has poorly aligned facets or isn’t very symmetrical. If a cutter wants to shape a well proportioned diamond, he won’t by shy about shedding weight to get great proportions. This is why different diamonds can have the exact same carat weight but can have very different dimensions.

Rough Diamonds

For example, these diamonds below appear to be different sizes when viewed from the top, but in fact they each weigh exactly the same!


This side view of the diamond shows how that is possible.


The tall, thin diamond on the left and the short, wide diamond on the right were polished to maximize weight. Only the diamond in the middle was polished with great cut in mind. In person, what you will see is the middle diamond is bright and scintillates with light, while the other two will appear much duller and darker.

The Trade-Offs

Diamond Cutting WheelA cutter has other tricks up his sleeve to maximize weight such as leaving extra material around the middle of the diamond (the girdle) or at the bottom (the culet), which creates a bulge of extra weight. Why would the cutter make any of these decisions? Because some people decide to buy the heaviest diamond for their money, even if it means sacrificing the diamond’s brilliance or performance. It’s kind of like buying the heaviest piece of steak at the supermarket even if has lots of fat or even bone inside. The benefit is that you get lots of food at the expense of taste. For them, it’s all about quantity, not quality.

On the other hand, a cutter who wants to create great light performance will polish away enough weight to ensure that everything lines up beautifully. He leaves no extra material for the sake of extra carat weight. The benefit is the fire and the signature performance that makes you say WOW. It’s kind of like buying smaller pieces of meat at the market, but making sure it is the most tender, most lean piece. In this case, it’s about balancing quality and quantity.

The Science of the Cut

How about some science to back it up? Some really smart people invented a scope to illustrate a diamond’s light performance and symmetry. It’s called an ASET scope and here are images of a well
proportioned diamond (left) and a poorly cut diamond (right).

Diamond Cuts

As you can see, the well proportioned diamond is symmetrical and has a clear, balanced pattern of light reflection. The diamond on the right is not proportional and light doesn’t reflect well.

Another technique for seeing proportion is using a diamond scope, which illustrates the hearts and arrows pattern of a well proportioned diamond. Ask a jeweler to show you diamonds under a scope to see for yourself.

Diamond Cut Technique

What Does A Cut Grade Mean?

Some independent gemological grading labs such GIA and AGS will give a certified diamond a Cut Grade along with a grade for carat weight, color and clarity. Cut Grades are relatively new and only a few laboratories offer them to help consumers gain a better understanding of cut. For example, a round diamond certified by the GIA today will be given a cut grade of either Poor, Good, Very Good, or Excellent.

Diamond Cut Guide Scale

Unfortunately, cut standards are very broad and there can be huge differences even within one grade. For example, we can show you two diamonds with excellent cut grades but they can look dramatically different to the naked eye. We’ve also seen diamonds with a Very Good cut grade on rare occasions even outshine and outperform an Excellent cut grade.

DiamondEventually, the cut grade standards will change and the certification labs will find a way to truly measure the light return and sparkle of each stone (the sooner, the better in our opinion). In the meantime, the Cut Grade helps but we will need our eyes to tell the difference. No jeweler ever buys a diamond without seeing it first and using the certificate as just a starting point. Neither should you. Look at plenty of diamonds so that you can see the difference for yourself, decide what is most important to you and make the right decision.

How to Choose the Cut That is Right For You

Anatomy of a DiamondWe believe that diamonds should perform and be brilliant, which means we gravitate towards nicely cut stones. But we’re realistic too and we understand that the size of the diamond is hugely important and that the key is finding the right balance between cut and weight, along with color and clarity too. We recommend you see diamonds for yourself to understand how to make the most of your budget. For example, you might see an immaculately cut 1 carat diamond, a decently cut 1.1 carat diamond and a poorly cut 1.2 carat diamond for a similar price. Nobody can tell you which one is right for you. So look at enough diamonds to understand the differences then make the right choice for yourself and your soon-to-be fiancée

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