What is Ideal Cut?

If you are looking for a diamond engagement ring, I am sure most of you will hear the term "Ideal Cut". Some might think that this represents the top quality diamond, some might think that it is equivalent to Triple Excellent, while some others might be more skeptical about it and wonder what the heck is an "Ideal Cut". Is it a marketing gimmick? Well, these days, for sure it is a marketing tool, but I won't call it a gimmick, in fact, I would just simply call it a marketing "tool" instead. This is because we can trace back to its lesser known origin - From a book called "Diamond Design: A Study of the Reflection and Refraction of Light in a Diamond" by Marcel Tolkowsky.

"Diamond Design: A Study of the Reflection and Refraction of Light in a Diamond" by Marcel Tolkowsky

Mr. Tolkowsky is a mathematician that relied on mathematical calculation to deduce the final ideal proportions of a diamond, which is also known as "The Ideal Cut" for the modern round brilliant diamond. Despite dating back to the year 1919, a hundred years ago, the research performed by Mr. Tolkowsky stand strong against the test of time because the properties of light remain constant forever.

Take a look at the best proportions calculated by Mr. Tolkoswky:

In the above images, the "alpha" sign represents the Pavilion Angle, while the "beta" sign represents the Crown Angle.

Do note that the numbers after the degree [°] symbol is in minute [']. Converting ""alpha" and "beta"values respectively, we will get:

Pavilion Angle: 40.75°

Crown Angle: 34.5°

While Mr. Tolkowsky uses mathematical calculation to reach the final conclusion of the ideal proportions, its result, comes close to the proportions of a sample pool of diamonds that are deemed the beautiful ones during that time! The cutters at that time determine the beautiful ones solely by their trained eyes.

So, moving into conclusion, we have this:

And mapping back into the modern round brilliant, we have this:

While this is the final result, we girdle thickness cannot be 0% in real life. Hence, the total depth will actually be more.

Here are the proportions of the diamonds used for comparison. I have converted it into degree [°] .

Diamond 1

35 CA

40.75 PA

58.7% Total Depth

15.7% Crown Height

43.0% Pavilion Depth

Diamond 2

35 CA

40.75 PA

61.4% Total Depth

18.6% Crown Height

42.8% Pavilion Depth

Diamond 3

34.5 CA

40 PA

55.4 Total Depth

13.3 Crown Height

42.1% Pavilion Depth

Diamond 4

33 CA

41 PA

58.5% Total Depth

15.7 Crown Height

42.8% Pavilion Depth

Diamond 5

34 CA

41 PA

60% Total Depth

17.8 Crown Height

42.2% Pavilion Depth

Diamond 6

34.3 CA

40.7 PA

58.9% Total Depth

16.2 Total Depth

42.6% Pavilion Depth

Now, compare the above values against the ACA specifications:

See the familiarity?

So here you go! The origins of "The Ideal Cut".

While there can be some other combinations that can perform well, it is really recommended that one should choose a diamond that meets the ACA specifications, or any other equivalent, as it is the bulls-eye and the possibility to perform well is higher.
1. IdealScope
2. ASET
3. H&A Scope

Interesting Read
Brian Gavin Diamonds:
https://www.briangavindiamonds.com/news/what-are-the-standards-for-ideal-cut-diamonds/?a_aid=myengexp

WhiteFlash:
https://www.whiteflash.com/a-cut-above-diamonds-specifications-and-qualifications/?a_aid=myengringexp

High Performance Diamonds (Dealer of Crafted by Infinity)
https://www.hpdiamonds.com/en-us/blog/blog-article/30/damaged-goods.htm

Diamond Design e-book:
https://archive.org/details/diamonddesign00tolk/page/n5