The Myth of the 60/60 Ideal Cut Diamond & Captivating Tales

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This 60/60 ideal cut diamond review is in response to the following inquiry by a client:

"Hello, I am seeking advice regarding the table % for a round diamond.  I want to choose a table that will display the greatest brilliance with a balance of dispersion. More brilliance. Period ha ha."

"I found an article [on United Diamonds] which at the bottom says that the president of the GIA shared the ideal table size for exceptional brilliance.  It says we should choose between 59 and 62 for table %. Yet I have found other tables that open the range to 53-58 as excellent and 58-60 is very good, so it has confused me."

"I read some texts here and it seems whoever does these reviews and articles is as picky as I am ha ha ha so my main concern is what should I aim for?" 

"Currently, I am on the hunt for a diamond with these specs: Shape: Round; Carat 1.75 +-; Cut: Excellent; Color: G; Clarity VS-2; Polish and Asymmetry: Excellent. Certification: GIA; Fluorescence: None.  Thanks a lot !!! F.M.”

The Legend of the 60-60 Ideal Cut Diamond:

Ha, Ha. I remember when Bill Boyajian, the former lab director of the GIA, made the statement that you are referring to. It was back in 1997, and what he actually said was:

"One example discovered in our investigation of modeling proportions of a round brilliant cut diamond revealed that, by our method of calculating brilliance, a 59 percent table is more brilliant than a 53 percent table, which was defined by Tolkowsky as "ideal”.  This calculation was based on maintaining all other angles defined by Tolkowsky.”

I’ve always thought the statement was issued because the GIA was reeling from getting knocked off their pedestal. In other words, that they were scrambling to try and discount the importance of proportions grading. Because the AGS Laboratory had just introduced their proportions grade study. After all, it did result in a substantial loss of business for the GIA Gem Trade Laboratory.

From my perspective, the GIA tried to dismiss the findings of the AGS Laboratory. And when it became clear that tactic was not going to work, they introduced their own cut grade system almost 10 yers later.

Of course, the amusing part was that the AGS Laboratory knocked them back to the stone age once again. Because they launched their new Light Performance grading platform right about the same time.

The Tolkowsky Cut Diamond:

In 1919, Marcel Tolkowsky, a member of a Belgian family of diamond cutters, published Diamond Design, the first recorded analysis of diamond proportions for the round brilliant cut diamond.

His work was based on modern theories of light behavior and his opinion of what proportions resulted in what many industry professionals considered to be the best possible balance of brilliance and dispersion of light until the mid-1990s.

Tolkowsky’s calculations indicated that for optimum brilliance a round brilliant cut diamond should be cut to the following angles and proportions:

  • 34.5° Crown Angle.
  • 40.75° Pavilion Angle.
  • 59.3% Total Depth (excluding girdle thickness) with 16.2% of the depth being comprised of the crown (top half of the diamond) and 43.1% representing the pavilion lower half of the diamond.
  • 53% Table based on the diamond’s overall diameter.

The American Ideal Cut Diamond:

Tolkowsky’s design is frequently referred to as the "American Ideal Cut” because diamond cutters in the United States began cutting it first.

Marcel Tolkowsky’s early model of brilliance set the stage for the modern round brilliant ideal cut diamond. However, the Hearts & Arrows Super Ideal cut diamonds are widely recognized as exhibiting superior light performance .

Note that Marcel Tolkowsky’s Diamond Design did not take girdle thickness into account. That means that a diamond truly cut to Tolkowsky proportions would have a zero percent, razor sharp, girdle edge. As a matter of fact, that would be prone to breakage and is impossible to produce.

In that case, we need to allow for a minimum girdle edge of 0.7% thin and that results in a deeper total depth of approximately 60%. As such, the girdle edge will be more durable and the design is more realistic from a production standpoint.

Tolkowsky Cut vs. Tolkowsky Range:

Do not be confused or misled by the appearance of the words "Tolkowsky Cut” on some diamond grading reports. The words "Tolkowsky Cut” do not necessarily mean that a diamond has been cut to Tolkowsky’s exact specifications.

Some laboratories like the European Gemological Laboratories (EGL) will say that a diamond is "Tolkowsky Cut” or within "Tolkowsky Range” if the diamond’s proportions are "within tolerance” of Tolkowsky’s original calculations.  According to the EGL the specifications for their "Tolkowsky Range” are as follows:

  • 33 – 36° Crown Angle.
  • 40 – 41.5° Pavilion Angle.
  • 56 – 60.5% Total Depth (excluding girdle thickness) with 14 – 16.5% of the depth being comprised of the crown (top half of the diamond) and 42 – 44% representing the pavilion lower half of the diamond.
  • 53 – 57% Table based on the diamond’s overall diameter.

Be that as it may, we've evaluated "Tolkowsky Cut” diamonds that scored overall proportions ratings as low as AGS-2 Very Good. In addition, we've even seen the words "Tolkowsky Cut” used by the EGL Laboratory to describe the overall proportions rating of fancy shape diamonds.

In other words, they're trying to apply Tolkowsky's design for rounds to other shapes like the Flanders Brilliant, marquise, and princess cut diamonds. Seriously, what gives with that?

How can Tolkowsky’s design for the modern round brilliant cut diamond apply for diamonds with completely different facet structures?

60/60 Ideal Cut Diamonds, Magic Beans, and Unicorn Horns:

When I first started as a diamond buyer back in 1985, the majority of old-timers told me: That diamonds with a 60% table diameter and a 60% total depth were the most brilliant diamonds available.

Interestingly enough, no mention of crown angle or pavilion angle was ever mentioned. When I asked them about whether the actual measurements for crown and pavilion angle mattered, I was told: That if the table diameter were cut to 60% and the total depth were cut to 60% then the crown angle and pavilion angle would automatically fall into place.

Apparently, anything with a 60% Table and 60% Total Depth would do and at the time I honestly didn’t know better. There wasn’t any such thing as mathematical ray tracing or computerized proportions analysis back then. And it was long before the GIA began to provide crown and pavilion angle measurements on their lab reports.

Under those circumstances, it was a relative free for all in the wild west of slinging diamonds for a living. Suffice to say that the 60/60 ideal cut diamond died a quick and tragic death the moment that the AGS Laboratory introduced proportions grading. Because the public suddenly became aware of the importance of the crown and pavilion angle of a diamond.

As a matter of fact, we were one of the first online diamond companies to purchase a Sarin computerized proportions analysis machine. In that case, we quickly realized that the diamond cutters were wrong.

Consequently. there was a wide range of possibilities for crown and pavilion angles to be found within the realm of 60-60 ideal cut diamonds. In other words, having a 60% table diameter and a 60% total depth was a guarantee of nothing.

Technology Killed the Mythical 60/60 Ideal Cut Diamond:

I believe that Bruce Harding first introduced mathematical ray tracing to the diamond industry around 1986. His work was later incorporated into various platforms such as computerized proportions analysis machines. Like the Sarin, OGI, and Helium, for example.

As well as the DiamCalc Software developed by Moscow University and the Holloway Cut Adviser that was first introduced to the public in November of 2001. Consequently, the Sarin, OGI,s, and DiamCalc software are used in every spectrum of the production and buying processes. 

Whereas, the Holloway Cut Adviser is best suited for consumer use. As a matter of fact, it provides people with an easy to understand evaluation of the performance potential. With that in mind, here is a screenshot of the HCA results for a Tolkowsky Cut Diamond.

You'll notice that the proportions reflect the exacting standards of his original diamond design from 1919. With the exception of the total depth being increased from 59.3% to 60%. Because we have to account for the fact that a girdle edge of at least 0.7% as explained above:

60-60 Ideal Cut Diamond vs Tolkowsky.

HCA Results for Tolkowsky Ideal Cut Diamond.

The HCA Results are Excellent:

The HCA results indicate that the diamond is likely to exhibit Excellent light return, fire, scintillation and spread.  Assuming that the diamond cutter also took the time to fine tune the degree of optical precision. In other words, there is consistency of facet shape size, and alignment.

In that case, there would not be any azimuth shift or facet yaw, so there isn't any obstruction. Obviously, this goes way beyond the basic meet-point-alignment standards for the basic symmetry grade on the lab report. As a matter of fact, the gemological labs don't even get into that stuff, but it's a critical component of light performance.

Remember What Bill Boyajian Said In 1997:

"One example discovered in our investigation of modeling proportions of a round brilliant cut diamond revealed that, by our method of calculating brilliance, a 59 percent table is more brilliant than a 53 percent table, which was defined by Tolkowsky as "ideal".  This calculation was based on maintaining all other angles defined by Tolkowsky."

Let's just put that to the test and punch those measurements into the Holloway Cut Adviser:

HCA Results 60-60 Ideal Cut Diamond.

HCA Results Based on GIA Model from 1997.

As you can see, while the estimated light return of the diamond remains excellent, the estimated fire and scintillation of the diamond dropped down to Very Good.  That is not really surprising since the "sweet spot” is a crown angle of 34.5 degrees offset by a pavilion angle of 40.8 degrees.

As a matter of fact, the table diameter of a diamond has very little to do with light return. That's because it is not one of the primary reflective mirrors of the diamond.

Consequently, it's the other facets that direct light around the inside of a diamond. Then reflect it back up towards the observer. But, as Bill Boyajian noted in his statement, it does have an effect upon the type of light return in terms of brilliance and dispersion.

Clarification of Gemological Terms:

Because people describe brilliance in different ways, I want to take a moment to address that as it applies to this article. In the first place, people tend to use the term brilliant to describe the overall visual impact of a diamond. While diamond cutters and professional diamond buyers break it down into the categories:

  • Brilliance (white sparkle).
  • Brightness (volume of light return).
  • Contrast Brilliance (light/dark sections).
  • Dispersion (colored sparkle/fire).
  • Scintillation (sparkle created by movement).

Quick Summations:

Brilliance is reflected white light or white sparkle.

Dispersion or "Fire” is reflected colored light or colored sparkle.

Scintillation is the flashes of light or sparkle created when you or the diamond is moving…

Light Performance is the amount of light being reflected back up towards the viewer as it exits the diamond.

Visual Performance is the amount of Sparkle Factor being created by the diamond as the direct result of precise facet alignment and structure.

With this in mind, when somebody says: "I want to buy the most brilliant diamond possible.” I tend to assume that they are actually looking for a high performance diamond.

In other words, they that are looking for one that is vibrant and exhibits a virtual balance of brilliance and dispersion with a high degree of scintillation. Because I'm thinking in terms of the actual gemological terminology outlined above. In that case, I always recommend the following range of proportions:

Table diameter between 53 – 57.5%.
Total Depth between 59 – 61.8%.
Crown angle between 34.3 – 34.9 degrees.
Pavilion angle between 40.6 – 40.9 degrees.

There are other combinations of measurements that will produce similar amounts and types of light return. However, this range eliminates a lot of the guesswork. As such, it will save you from having to punch numbers into the HCA all day long.

Selecting a Stunning Looking Diamond:

All right now that I’ve had the chance to thoroughly explain all of the reasons why I believe that diamonds with a 59% table diameter are not necessarily more brilliant than diamonds with a 53% table even when the other measurements of the diamond fall within my exacting standards.

Let’s go ahead and search for options which meet this particular request… The first thing that I’m going to do is Search for Diamonds at Blue Nile. To begin with, we'll  set the advanced options to a total depth of 60% and a table diameter of 59%. Then we'll set the clarity grade to VS-2 and G-color . Of courese, we'll be looking for GIA Excellent polish and symmetry with faint to no fluorescence.

My Blue Nile Diamond Search Produced 4 Options:

Note: Blue Nile changed the format of how deep links were created when they switched their affiliate network. Thus, the original links to the following diamonds were broken and have been replaced with links o their diamond search page. As a matter of fact, that's just as well these options have probably sold by now.

Please use my free Diamond Concierge Service if you would like me to help you find the best options currently available, but the information that can be obtained by reading the article is still applicable even if the diamond details pages can not be accessed.

Diamond Review #1:

Blue Nile 1.70 carat, G-color, VS-2 clarity diamond which has a table diameter of 59% and a total depth of 60.9% with a crown angle of 33.5° offset by a pavilion angle of 41.2°with a medium to slightly thick, faceted girdle and no culet with an overall cut grade of GIA Excellent.  If we punch the numbers into the HCA we get a rating of Very Good for light performance, fire, scintillation, and spread.  I think we can do better…

Diamond Review #2:

Next, we have this Blue Nile 1.71 carat, G-color, VS-2 clarity diamond which has a table diameter of 59% with a total depth of 60.9% with a crown angle of 34.5° and a pavilion angle of 40.8° with a thin to slightly thick, faceted girdle and no culet with an overall cut rating of GIA Excellent.

Note that this diamond actually does have the crown angle and pavilion angle defined by Marcel Tolkowsky in his Diamond Design of 1919. However, if we punch the numbers into the HCA we get Excellent for Light Return (no surprise, I explained this previously) but only Very Good for Fire, Dispersion and Scintillation.  It is however the best of the choices currently available from Blue Nile within the confines of this particular diamond search request.

Diamond Review #3:

Finally, we have this Blue Nile 1.73 carat, G-color, VS-2 clarity diamond with a table diameter of 59% and a total depth of 60.5%. The crown angle is 35.0° offset by a pavilion angle of 41.2° with a thin to medium, faceted girdle. The culet is very small culet and the overall cut grade is GIA Excellent.

If you punch the numbers from this diamond into the Holloway Cut Adviser and you get Very Good for Light Return. Only Good for Fire, Good for Dispersion and Very Good for Spread.

Diamond Review #4:

The next diamond which I found is this 1.706 carat, G-color, VS-1 clarity Signature Hearts and Arrows Diamond from Brian Gavin which has a total depth of 61.9% with a table diameter of 55.9% and a crown angle of 34.8 degrees which is offset by a pavilion angle of 40.9 degrees with a thin to medium, faceted girdle and a pointed culet with negligible fluorescence.

While the HCA still gives this diamond a rating of Excellent for Light Return and Very Good for all other factors, this diamond was graded by the AGS Laboratory on their Platinum Light Performance grading platform which takes into consideration a scan of the diamond using their Angular Spectrum Evaluation Tool (ASET) which evaluates the diamond from approximately 244 different vantage points.

This diamond also exhibits a crisp and complete pattern of hearts and arrows which indicates that the diamond is not suffering from a significant amount of Azimuth Shift and thus the Visual Performance or Sparkle Factor of the diamond is going to be top-notch.  It also looks phenomenal through an Ideal Scope.

In Absence of More Information:

Now the Blue Nile 1.71 carat, G-color, VS-2 clarity diamond might look equally as good when viewed through a Hearts and Arrows scope and an Ideal Scope. However, they don’t provide those images on their web site, so you can only hope for the best.

I continued my search and found this 1.71 carat, G-color, VS-2 clarity diamond from James Allen. it has a total depth of 61.0% with a table diameter of 59%. The crown angle is 34.5 degrees offset by a pavilion angle of 40.8 degrees with a medium to slightly thick, faceted girdle. The overall cut grade is GIA Excellent with no culet.

The HCA gives this diamond Excellent for Light Return and Very Good for all other factors.  Like Blue Nile, James Allen does not provide reflector scope images of this diamond. Therefore, we don't have the additional insight into diamond cut quality and visual performance.

Last, but not least, we have this 1.76 carat, G-color, VS-2 clarity diamond from James Allen. It has a total depth of 60.8% with a table diameter of 57%. The crown angle is 34.5 degrees offset by a pavilion angle of 40.6 degrees with a medium to slightly thick, faceted girdle and no culet.

The HCA gives this diamond a rating of Excellent for Light Performance, Fire and Scintillation which is promising… now I’d just like to see the scope images, let me know if you want me to ask for them.

Would you like help finding a diamond?

As you can see from this detailed response, I take the challenge of finding the right diamond for our clients quite seriously. Plus, I strive to provide you with an impartial review of each diamond regardless of who the vendor is.

Drop me a note if you'd like help finding a diamond or if you have diamond related questions.

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