If you had been doing some research on buying diamond rings online, you might have heard of a man named Fred Cueller aka “The Diamond Guy”. You might also have come across a term coined by him called the “warped girdle” and this is a misleading term that I want to address in this article.
You see, the problem here is that “The Diamond Guy” advices consumers to look carefully at proportion figures for the diamond’s crown, pavilion, and girdle. If the percentages (crown, pavilion & girdle) do not add up to the total of the depth percentage, then that diamond is likely to be ‘warped’ and you should avoid buying the stone.
This is some serious misinformation and I’ll explain to you why below…
The formula Fred Cueller defines for determining diamond warpage appears to be simple math.
Total Depth = Crown Height + Maximum Girdle Thickness + Pavilion Height
While I won’t totally discredit everything Fred Cueller had written in his book “How to Buy a Diamond“, readers can get confused and misguided with the term “warped diamonds”. This confusion stems from the lack of explanations when he tries to over-simplify things with the above equation.
You see, the measurements of a diamond’s proportions can get pretty technical. Most consumers are not well-informed and even the majority of jewelers don’t even know understand it themselves.
Certificates issued by gemological labs also offer no explanations on how girdle thickness measurements are taken and displayed. Instead, you need to do advanced research on the Internet or via other academic sources like gemological books in order to find out more.
For your convenience, I had done the prior research on your behalf. You can refer to GIA’s webpage to learn more about how the diamond’s proportions are measured and displayed. That said, unless you have a keen eye for details or have a solid background in academic science, most of the technical data will sound gibberish to you. To keep things simple and understandable, I did a summary to touch only on the critical stuff here.
In essence, the total depth% of the diamond is calculated and rounded to the nearest 0.1%.
The crown height %, pavilion depth % and girdle thickness % are calculated based on averages and rounded to the nearest 0.5%.
Based on the formula stated by Fred Cueller, we are attempting match an accurate total depth % measurement (captured with a Sarin machine from the top of table facet to culet) against the sum of 3 inaccurate values that had been individually rounded.
In statistics, the compounding of errors will give rise to even bigger errors! I will explain this using a real-life example of the proportions diagram extracted from a GIA report.
Ok, Let’s Count Now…
Total Depth (62.0%) = 15.5% (crown) + 4.0% (girdle) + 43.0% (pavilion)
Oh gosh! It doesn’t add up! Is this diamond having serious issues with it? So, what’s the explanation behind this? To do a correct (and hardcore) analysis, you will need an in-depth Helium or Sarin report that shows you all the data on facet angles and proportions.
For an example’s sake, let me show you a quick calculation due to rounding errors that might be a reason behind why numbers don’t add up.
Total Depth = 15.31% (15.5%) + 3.76% (4.0%) + 42.93% (43.0%)
= 62.0% (62.5%)
Black = Simulated Values Blue = Values That Were Rounded Off by GIA
The rounded numbers give rise to errors that result in a higher calculated depth!
Bear in mind that these are well cut diamonds for light performance and have top notch cut precision. There’s nothing wrong with these stones and both pass my standards to be purchase-worthy.
When Fred Cueller uses the term warped to label diamonds with these discrepancies, that’s only one man’s view of selecting diamonds and it isn’t very accurate. The truth is, Fred Cueller doesn’t even take a scientific approach to associate “warpage” with a diamond’s light performance. The point I am trying to bring across here is that even if the numbers do match up, it doesn’t guarantee a diamond’s beauty.
By the way, it’s no coincidence that other diamonds are “warped” in his view except for those sold by him. There’s a more sinister agenda at work here to scare people away from buying diamonds from other honest jewelers!
Lastly, there are ideally cut diamonds with nice optical symmetry and superb light return that would often fall under Cueller’s classification of ‘bad’ diamonds. If you followed his advice blindly, you could be passing up on some really great stones!
With the example that I had shown above, I hope this clears up the questions on why numbers don’t add up. They sometimes don’t because of the way GIA reports measurements and NOT because there are issues with the diamond.
With a little common sense, you probably know you need to avoid stones with large girdle variations like “very thin – extremely thick”. Such huge variations are tell-tale signs of poorly cut stones and weight retention tricks employed by cutters. Obviously, you don’t need an expert to tell you they aren’t good choices.
Here’s my last piece of advice, don’t get too caught up with numbers. At the end of the day, what you (as a consumer) want is a nice looking diamond and the best way to achieve that is to utilize tools like the Idealscope/ASET scope when making buying decisions.