Marcel Tolkowsky revolutionized the world of round brilliant diamonds in 1919 when he published his landmark book titled “Diamond Design“. In his book, he wrote about a set of proportions that would yield in a diamond with maximum beauty, fire and scintillation based on mathematical calculations. Ever since the epic publication, Tolkowsky’s findings were widely applied in diamond polishing by cutters around the world.
Marcel Tolkowsky’s ideal proportions for a round brilliant diamond.
In more modern times, much has changed as Tolkowsky’s groundbreaking discoveries were further developed upon. With the help of specialized studies and technological advancement, researchers from GIA & AGS had published scientific journals that changed the way we polish and buy diamonds.
One of the major breakthroughs made was the discovery that ideal cut diamonds do not have to follow a single set of proportions as set forth in Tolkowsky’s original dissertation. In fact, a diamond could be polished within a range of proportions and it would still display ideal optics.
|Table %||52.4% to 57.5%|
|Depth %||56.88% to 63.92%|
|Crown Angle||33.7° to 35.8°|
|Pavilion Angle||40.2° to 41.25°|
|Girdle Thickness||Thin – Medium|
Source: The Ideal Cut: A Consumer’s Guide.
*Note: The above historical table should be used as a reference only. With modern day research, the Tolkowsky proportions have been further refined. If you are looking for a diamond that exhibits superior brilliance and sparkle, scroll down to use MY proven table of ideal cut diamond proportions instead.
In Tolkowsky’s initial publication, he stated that the ideal cut diamond should only have a table proportion of 53%. However, it has now been scientifically proven that an ideal cut could have proportions outside of this value and diamonds with slightly bigger tables can also achieve ideal optical properties.
Both GIA & AGS had also came up with comprehensive tables of proportions and cutting guidelines. You can download the AGS cutting guidelines here and GIA proportions chart here to do your own comparisons and analysis.
Over the years of examining and analyzing diamonds, I had tabulated my own set of parameters for selecting a ideal cut round diamonds. While it is modeled after Tolkowsky’s initial findings and studies from GIA/AGS, my parameters are much more stringent.
This tighter set of parameters helps to filter diamonds that are the cream of the crop and I personally use it to handpick diamonds for myself. I strongly recommend that you apply these parameters when searching for your own diamonds. It will not only help you save time but weed out the badly cut diamonds as well.
Here, I want to highlight that proportions should only serve as an initial filtering process. In order to confirm light performance, you will need to rely on idealscope or ASET images for analysis.
|Table %||54.0% to 57.0%|
|Depth %||61.0% to 62.5%|
|Crown Angle||34.0° to 35.0°|
|Pavilion Angle||40.6° to 41.0°|
|Lower Girdles||75% to 80%|
|Star Facets||50% to 55%|
|Girdle Thickness||T – M – ST|
Now, with all the technical specifications laid out, you might assume that all the diamonds in the market should be polished to ideal proportions if cutters simply followed a standard formula. However, the truth is far from that.
In fact, it is estimated that 90% of the round diamonds are cut to dismal proportions by choice.
As a consumer, here’s your bottom line when selecting a round diamond for light performance. There’s ABSOLUTELY NO wriggle room when it comes to proportions. Even if a diamond just barely failed to meet these proportions, it is an INSTANT REJECTION and you will have to dump the stone.
When buying diamonds, the ideal proportions matter and precision is required. Even if a diamond has just a 0.2° deviation in pavilion angles (41.2°), it WILL impact light performance. It doesn’t matter whether it has been graded as a triple excellent diamond or a triple ideal stone.
I have to reemphasize here: if the proportions aren’t correct, light performance will be adversely affected. (Granted, there could be outliers but the odds of you finding a well cut diamond outside of these proportions are extremely low.)
Despite my advice, I know there are some readers and internet trolls who will still say stuff like: “Does having something slightly out of the range REALLY affect the light performance or something like that?” or “So what if the pavilion angle is 0.2°? If it were such a big issue, why did GIA still grade the diamond as a triple excellent rating?”.
Well, check out the examples of GIA triple excellent diamonds below. These are diamonds with near misses in proportions and I want you to look at how a small variation can affect the light return of the diamond in a big way.
The ASET imagery reveals significant light leakage and poor edge-to-edge brightness for both diamonds.
Diamond light performance is bounded by the laws of physics and it has a direct correlation to the facet proportions. So, if you are thinking about buying a diamond with proportions that don’t conform to the table I laid above, you better be asking yourself a big fat WHY.
Why should you settle for a diamond with less than ideal proportions when there are literally hundreds of diamonds out there available in the market? In contrast, let me show you what a diamond that is cut for ideal light performance looks like.
This diamond has top notch light performance and extreme cut precision.
In fact, I’ve recently purchased the diamond above and you can read the full review of the engagement ring here. I’ve even recorded a video that compares how well the diamond sparkles in various environments.
Although I’ve been in the trade for many years, I’m also a consumer like many readers as well. And when I shop for a diamond, I’m super anal about cut quality because I want the most sparkly diamond that money can buy.