Tolkowsky Ideal Cut Diamond Proportions

If you’re in the market for a beautiful diamond, it’s likely you’ve been doing some researching into the all-important Four C’s. Your research has probably led you to the understanding that the cut of a diamond is the most important of all quality grades – and that would be correct.

If you are lost in a world of Excellent cut, Ideal cut and Super-Ideal cut jargon, this article will take you right back to basics, to the man who is widely credited with conceiving the ideal-cut proportions for a diamond.

A Brief History of Diamond Cutting

Before I take you to the man of the hour, Tolkowsky, this brief history of diamond cuts will give you some idea of how important Tolkowsky’s discovery was.

History of diamond cutting

This table gives a clear synopsis of the long journey towards the modern brilliant cut that we adore. From the earliest and most rudimental cuts, right up to the old European cut, developments in cutting tools and other equipment allowed experts to refine the process, adding more facets to give depth, shape and eventually, sparkle.

Tolkowsky’s role in the progression of cut lies in the precise, mathematical calculations that took into consideration the potential for fire and brilliance within a diamond and how best to unleash it.

Marcel Tolkowsky

Born in 1899, Marcel Tolkowsky was an engineer based in the diamond capital of the world, Belgium. He came from a family of diamond cutters hailing from Poland and to this day many of his younger relatives continue his work in the world of diamond cutting.

While studying at the University of London, a large part of Tolkowsky’s PHD was focused on the grinding of diamonds. In his book Diamond Design, he first printed the specifications for an ideal cut (also known as the American Standard, the Tolkowsky cut, the Tolkowsky Brilliant or the American Ideal Cut). His contribution to our understanding of diamonds set a new standard and although diamond cutting has evolved since Tolkowsky’s specifications were published, they created the foundations for the ideal-cuts that are sold all over the world today.

Tolkowsky’s Ideal Cut Specifications

The Tolkowsky formula is concerned with round brilliant diamonds (although the term round brilliant arrived after his ideal cut theory was printed). He suggested that the ideal cutting proportions which would yield the best light return are as follows:

Crown Angle 34.5º
Pavilion Angle 40.75º
Total Depth 59.3%
Table Diameter 53%
Crown Height 16.2%
Pavilion Depth 43.1%

The first issue identified with Tolkowsky’s design concerns girdle thickness. Although Tolkowsky mentions girdle thickness in Diamond Design, he does not give any specifications. Historians and diamond experts have surmised that Tolkowsky’s calculations correlate to a knife-edge girdle – this is no longer considered optimal for round brilliant diamonds as there is a risk of damage. It also does not account for optical precision (relating to hearts and arrows) – it is optical precision that allows the properties of brilliance, fire and scintillation to be seen to their full potential.

Naturally, progression in diamond cutting and diamond analysis have allowed us to build upon the Tolkowsky framework, but another factor which necessitates tweaks to his formula is much more straight forward: light.

Lighting environments and light sources have also modernized and as a result the way a diamond needs to handle light has changed too. Strip and fluorescent lighting wouldn’t have been a consideration for Tolkowsky and although his design accounts for fire and brilliance, there is no mention of scintillation. Flash scintillation attributes to black and white contrast in a diamond; this contrast creates a blinking effect causing white flashes of sparkle.

Modern Ideal-Cut Diamonds

The framework set by Marcel Tolkowsky has proved invaluable in the continuing quest for ideal-cut diamonds and exceptional light performance.

The way that we cut diamonds has changed – using lasers, diamond cutters can be more precise than ever in a bid to deliver the best results. Unfortunately, for the mass market, carat is king. Cutters are often encouraged to sacrifice quality in favour of carat weight and this explains the masses of low-quality diamonds that continue to be sold and traded across the world.

However, if you are looking for diamonds which take the Tolkowsky design to the next level, they are out there.

Most notably, the AGS have used cutting edge diamond analysis tools to build upon Tolkowsky’s findings and create their cut grades.

AGS cut scale

The GIA have also used Tolkowsky’s research in their cut gradings, however while the GIA remain one of the most internationally respected gem labs, the AGS is credited with taking a more scrutinous approach to cut quality and ideal cut diamonds.

The pinnacle of ideal cut diamonds and stringent specifications can be found in in-house collections that go above and beyond the gem lab specs. An excellent example of this is Whiteflash’s A CUT ABOVE® range. The table below shows Tolkowsky’s originals specs for a round brilliant and measures them against a GIA ‘Excellent’ cut grade and a Whiteflash, A CUT ABOVE® diamond.

Measurements Tolkowsky GIA Excellent A CUT ABOVE®
Depth % 59.3% 58.6-64.1% 59.5-62%
Table % 53% 52-62% 53-58%
Girdle N/A T-M-ST T-M-ST
Culet N/A N-P-S-M N-P-S
Polish Grade N/A EX-VG Ideal
Symmetry Grade N/A EX-VG Ideal
Crown Angle 34.5 31.5-36.5 34-35
Pavilion Angle 43.1% 40.6-41.8% 40.6-40.9%

This table shows the tiny margins within the A CUT ABOVE® parameters – only a tiny percentage of the world’s diamonds tick all the boxes and earn the A CUT ABOVE® title. They describe it as ‘the bulls-eye’ of diamond performance.

I am unable to reference Blue Nile and James Allen as they don’t provide transparent specifications of the vast majority of their diamonds online, this is where Whiteflash differentiates themselves.

GIA-vs-AGS-vs-A-CUT-ABOVE-Diamond

Image Courtesy of Whiteflash

The average consumer may find these figures confusing; it may appear that though the original Tolkowsky specifications are more precise, working on a single figure rather than a bracket of acceptable figures. In fact, modern ideal-cut specifications take into account the precise workings of the facets – on this understanding, narrow margins of difference allow for balance within the diamond. Modern specifications also account for the girdle thickness which was missing in the Tolkowsky design.

Should I Buy a Tolkowsky Ideal-Cut Diamond?

Tolkowsky’s incredible contribution to the diamond world deserves acknowledgement. Sadly, the Tolkowsky name continues to be attached to average looking diamonds and used as nothing more than a marketing tool. Highstreets jewelers and low-quality vendors are all likely to sell some variation of a ‘Tolkowsky collection’ – as the original diamond design was lacking in many areas (scintillation, optical precision, girdle thickness etc) it leaves the entire formula open to wide interpretation. Furthermore, as diamond technologies have advanced, experts have filled in the blanks and realised that while Tolkowsky’s findings were the beginning of the journey, they were not the definitive standard for round brilliant diamonds.

If you are interested in ideal or super-ideal cut diamonds, I suggest taking a look at the Whiteflash and focus on the A CUT ABOVE® range. They have highly detailed education pages that empower their customers with all the necessary knowledge when it comes to the cut of their diamonds. They offer light performance reports as standard, including ASET, Hearts and Arrows and Sarin reports – not only do these reports give an accurate and clear idea of light performance, they are far more tangible to the average buyer than a list of percentages. If however you’re looking for fancy shape diamonds take a look at James Allen and if you’re on a tight budget then Blue Nile might be a good option for you.

Richard Jenkins, The Diamond Guru

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