When we think of an engagement ring, one image comes to mind: a sparkly round cut diamond! This shape is the vanilla of engagement rings, but it’s never bland, it has always reigned supreme.
Some would try to be edgy and opt for fancy shapes; little do they know that the magic behind the round diamond lies in its cut proportions. So, don’t be fooled by its basic form because it can exhibit a bright and fiery sparkle that no other diamond shape can ever imitate.
Now, before diving deep into the details of the round cut, I encourage you to read my posts on the Diamond 4Cs: cut, color, carat, and clarity. These pages will serve as your prelude/refresher to better understand the nature of round cut diamonds. If there’s no need for an intro, let’s get started!
Why Choose Round Cut?
1. Round Cut Diamonds Are Universal
The round cut diamond hasn’t always been the universal choice for engagement rings. In fact, we have the De Beers commercial to thank for it! With their ingenious marketing, the diamond is now seen as the universal symbol of love.
(I have written a separate post on De Beers’ marketing methods if you’re intrigued by this backstory.)
Today, 70% of all diamond engagement rings consist of round cuts. The calming round form with its association with eternity evokes neutral reactions at worst, but very positive responses at best. I have never heard anyone say that he or she considers a round cut diamond to be unappealing.
On that premise, choosing a round cut diamond eradicates the risk of your lady not liking the diamond shape you have selected. Although, it’s not meant to be just a safe bet – it is a sure win!
2. Round Cut Diamonds Exhibit Supreme Light Performance
More importantly, ideal round cut diamonds provide a maximum light return compared to other shapes. The proportions of a well-cut round with its 57 facets allow for nearly 100 % light return.
You can see it quite easily if you compare the ASET images of perfect round and princess cut diamonds. Although the princess cut is the second most brilliant diamond shape, it has much more areas of less intense return (green) compared to a round cut:
This means that round cut diamonds reflect virtually all the light that enters back to the viewer’s eye. Such a high percentage of brilliance is not possible with any other diamond shape! This is why a perfectly cut round diamond has the most amount of fire and scintillation compared to other cuts.
3. Round Cut Diamonds Show the Least Amount of Body Color
The body color in a round cut is the most difficult to make out. For instance, there are diamond shapes that are more prone to showing off body color as they tend to trap light in a different manner.
Usually, you would not be able to tell the difference between a G and an H color. But if you would compare this H-colored emerald cut diamond to this G-colored round cut, you will definitely be able to spot the color variation. Don’t you think that the perceived difference in body color is astounding?
Check out James Allen’s diamond color simulator if you want to see what each color grade of round cuts actually looks like:
That said, round cut diamonds are the best-suited diamonds to compromise on color and get a bigger bang for your buck!
(In my post on diamond color, I explain which color grade to choose for each ring metal to help you maximize your budget.)
What are the Ideal Proportions for a Round Excellent Cut Diamond?
If you have decided to buy a round cut diamond, you would want to choose one that has the maximum amount of brilliance, fire, and scintillation. For this to happen, you must opt for a diamond with the best proportions. As you might know, the proportions are graded within the “cut” of the 4Cs.
The best cut grade is “Excellent” (graded by GIA) or “Ideal” (graded by AGS). In my opinion, you should never compromise on the diamond cut because it is the exact dimensions that determine how lively, bright, and sparkly it will look! Furthermore, you get an automatic boost in all the other 3Cs if you choose an “Excellent” cut.
Okay, but what if you have two diamonds with the same cut grade, and you want to know which one will have a better light performance? This is when your knowledge of cut proportions comes into play!
The Tolkowsky Ideal Cut
In 1919, the mathematician and renowned gemologist, Marcel Tolkowsky published his findings for the perfect diamond proportions in his thesis entitled “Diamond Design, A Study of the Reflection and Refraction of Light in a Diamond.” All diamonds that were within the parameters of the so-called Tolkowsky Ideal Cut were considered to have an excellent light return.
Most recent research by prominent gemological grading institutes has found that the round cut diamonds’ ideal proportions for maximum light performance are somewhat close to the original Tolkowsky Ideal Cut. (You can find the exact GIA proportions chart or AGS proportions chart here.)
The table on the left shows the commonly acknowledged cut proportions for an Excellent Cut.
These dimensions guarantee that your round diamond bears exquisite brilliance, fire, and scintillation.
Super Ideal Round Cut Diamonds
Now, what if you have several diamonds that are cut within the parameters above? For sure, these diamonds will have a good light performance.
But what if you want to find a diamond with an exceptional sparkle? Then, you would have to pick a one that lies within the proportions of a super ideal cut! These parameters are even stricter than GIA or AGS’ criteria for an Excellent/Ideal cut. It guarantees that your diamond is among the very best!
The Easiest Way to Find Super Ideal Cut Diamonds:
Simply use this link for the pre-loaded set of parameters for super ideal cut diamonds. You may adjust the other settings to fit the range of color, clarity, carat weight, and price that you are interested in. Then, open each diamond in a new tab, click on the icon of the grading lab, and filter out all diamonds that do not meet the following criteria:
Crown angle between 34.0° – 35.0°
Pavilion angle between 40.6° – 41.0°
Culet: GIA “none” or AGS “pointed” (it is the same thing)
Polish / Symmetry: GIA Excellent or AGS Ideal
This way, you can easily find super ideal cuts by yourself! If you’re already sold, Brian Gavin and Whiteflash are excellent choices. All of their signature diamonds are also Hearts and Arrows which are diamonds with the highest degree of symmetry.
(Know more about hearts and arrows on this page.)
What’s the Difference Between an Excellent Cut and a Poor Cut?
Let’s see the difference between a well-cut diamond and one with bad proportions from all angles. Just compare these two diamonds to each other:
The diamond on the left is within super ideal cut proportions and exhibits a lot of dispersion and scintillation. You can see that the sparkle and fire are pretty balanced. The diamond on the right, however, is outside the super ideal proportions and has considerably less sparkle.
Naturally, the further you go outside super ideal dimensions, the worse the light performance is going to be! If you have several diamonds that fall within these standards, it might be hard to choose “the one.” You can always contact me in such a case, and I will be more than glad to help you out.
How to Find a Well-Performing Round Cut Diamond
1. Filter with the Holloway Cut Advisor Tool
Simply put: Narrow down your choices to the three diamonds you like most. Your selection shouldn't contain any poor performing diamond. Meaning, they should have superb optical performance.
In order to filter out all the poor performing gems, there is a very useful (and free!) tool called the Holloway Cut Advisor (HCA):
The HCA was developed by Gary Holloway who has been active in the diamond industry since the early 70s. To use the Holloway Cut tool, you would have to type in your diamond's parameters and click “go.” It will then return a score ranging from 0 – 10 to you. The desired score has to be below 2!
This tool assesses the light return and spread of a diamond and gives a Total Visual Performance score. Thus, you can use it to weed out any diamond that has a rating above 2.
Please note, however, that the Holloway Cut Advisor is only good for getting rid of diamonds with a weak light performance. It’s merely a rejection tool and should never be used as a selection tool.
(Read my take on the Holloway Cut Advisor Cons if you want to know more details.)
Also, please be aware that the HCA only takes into account the cut of a diamond. You still have to make sure that the clarity grade is good enough. Now, it goes without saying that if you buy a diamond within the super ideal proportions, your diamond will automatically have a score below 2!
2. Check the Ideal Scope Images
After weeding out low-performing diamonds, you should have a specific look at light performance. For you to do so, compare their Ideal Scope images and see which diamond leaks the most light:
With the two diamonds above, you can see that the one on the right has more white areas than the left diamond. White color indicates areas of white leakage which mean that the diamond on the right will not sparkle as brilliantly as the diamond on the left. But without the Ideal Scope images, you would never know because both diamonds have very similar proportions.
(Read my article on Ideal Scope image evaluation if you want to know more!)
3. Never Buy Round Cut Diamonds Blindly
Online stores like James Allen, Brian Gavin, and Whiteflash offer Ideal Scope images for all their diamonds. This is a rare service and even the biggest online vendor Blue Nile, doesn’t provide any additional images – so you are literally buying blindly!
Take note that wherever you may shop, you should never purchase a diamond without having a thorough look at its Ideal Scope image. Unless of course, you don’t care about light performance.
Another thing to look out for are high definition magnified 360° videos in up to 40x magnification! This way you get to see exactly how the diamond behaves in light. James Allen does that and is currently the only shop offering free return shipping in case you didn’t like the diamond for whatever reason.
The round cut is deemed as the favorite because it’s the Godfather of engagement rings. Its popularity goes a long way, beyond its classic form. Whether you are into minimal style, a trend-follower, or a technical shopper, round cut diamonds fit the bill.
Should you have any questions about round cut diamonds, or if you feel stuck in your search, comment below or just write me a mail! I usually respond within 24 hours. 🙂