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Ideal Cut Diamonds Buying Guide

Ideal cut diamonds offer the highest degree of light return and superior light performance. There are  many definitions for ideal cut diamonds to be found online. The majority of those parameters seem to describe ideal cut diamonds which do not meet my selection criteria. They might have ideal proportions that fall within the spectrum defined for the zero ideal cut proportions rating. They might even have an overall cut grade of AGS Ideal-0 or GIA Excellent. But that does not necessarily mean that those “ideal cut diamonds” will exhibit the best light performance. The parameters for the ideal cut diamond classification are rather broad by my standards. The purpose of this diamond buying tutorial is to provide you with the knowledge necessary to select the best ideal cut diamonds available.

How to Pick the Best Ideal Cut Diamonds:

Ideal Cut Diamonds Brian Gavin SignatureContrary to what you might be led to believe, there is more to buying ideal cut diamonds than limiting your search to AGS Ideal or GIA Excellent cut diamonds. The degree of optical precision should also be taken into account. Unfortunately, optical precision is not part of the grading criteria for the AGS Ideal-0 or GIA Excellent cut grades. Thus it is up to you to judge the degree of optical precision. The only way to do that is to look at the diamonds as seen through reflector scopes designed for that purpose. This series of photographs show reflector scope images for a Brian Gavin Signature round hearts and arrows diamond. Brian Gavin provides Hearts and Arrows Scope, ASET Scope, and Ideal Scope images for all Signature diamonds. The hearts pattern appears to be picture perfect, thus we know that the degree of optical precision is exceptional. The ASET Scope image looks fantastic. The Ideal Scope images looks exceptional. This diamond will be bright, lively and vibrant!

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The proportions of a diamond are a critical component. The volume of light return exhibited by an ideal cut diamond is dictated by the pavilion angle. The pavilion is the lower portion of a diamond. The balance of brilliance (white sparkle) and dispersion (colored sparkle) is dictated by the crown angle. The crown is the upper half of the diamond. If the table diameter of the diamond is too large or too small, it can result in light leakage and poor light performance. The table facet is the large flat facet that appears on top of a diamond.

The best ideal cut diamonds exhibit a high volume of light return and a virtual balance of brilliance and dispersion. Brilliance is white light or white sparkle. Dispersion is colored sparkle or fire. The following set of proportions is most likely to deliver the highest volume of light return and a balance of brilliance and dispersion:

  • Total depth between 59 – 61.8%
  • Table diameter between 53 – 58%
  • Crown angle between 34.3 – 34.9 degrees
  • Pavilion angle between 40.6 – 40.9 degrees
  • Lower girdle facets between 75 – 78%
  • Star facets between 45 – 50%
  • Girdle thickness between thin and slightly thick
  • Culet: AGS pointed or GIA none

This set of proportions falls within the middle of the spectrum designated for the zero ideal cut proportions rating. Ideal cut diamonds with these proportions, and an overall cut grade of AGS Ideal-0 or GIA Excellent, which exhibit a crisp and complete pattern of hearts and arrows are often referred to as super ideal cut diamonds. There are other combinations of proportions that are acceptable. More information can be found in the article 15 Seconds to Diamond Buying Success.

Classifications of Ideal Cut Diamonds:

The term “ideal cut diamonds” is used to describe a wide variety of options. It has become kind of a catch phrase that is used to describe a lot of diamonds which are pretty far from what I consider to be ideal. Let’s try to straighten that out.

I don’t agree with the proportions parameters adhered to by the AGS and GIA gemological laboratories. I feel that they are much too broad. The conspiracy theorist in me is convinced that these organizations have succumbed to industry pressure to make it easier to hit the AGS Ideal-0 and GIA Excellent cut grades. The fact that GIA makes a practice of rounding off some of the measurements provided on their diamond grading reports, after averaging those measurements to begin with is patently absurd.

Classifying ideal cut diamonds as such when they have a polish or symmetry grade of very good is equally absurd. If a diamond has a polish or symmetry grade of very good, it is not ideal cut by my standards. Accept nothing less than AGS Ideal or GIA Excellent with proportions as outlined above.

Hearts and Arrows Super Ideal Cut Diamonds:

  • Super Ideal Proportions as outlined above.
  • AGS Ideal-0 or GIA Excellent cut.
  • AGS Ideal or GIA Excellent Polish and Symmetry.
  • Exhibits 8 Crisp, Symmetrical Hearts
  • Exhibits 8 Crisp, Symmetrical Arrows

I highly recommend reading this tutorial on the creation of hearts and arrows patterns in round diamonds. There is a lot that goes into the assessment of whether a diamond is hearts and arrows or not. Certainly too much to address in this article. Especially since it’s already been addressed in-depth there.

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AGS Ideal Light Performance grading report, image courtesy of AGSLAGS Ideal Cut Diamonds are explained thoroughly in that article. Once again, I strongly recommend adhering to the range of proportions outlined above. Stick with options graded on the AGS Light Performance grading platform which features the ASET scan. Without the ASET scan, you won’t be able to determine how evenly light is being reflected throughout the diamond. The insight provided by the ASET scan is portrayed on this image which is provided courtesy of the AGS Laboratory. The right side of the image shows how the diamond looks when viewed through an ASET Scope. It makes it possible to determine how evenly light is being distributed throughout the diamond. But also lets us know how bright the diamond will be. Where the diamond is gathering light from within the hemisphere. The degree of contrast being exhibited by the diamond. It even provides some insight as to the degree of light leakage. A lot of dealers hate this technology. The reason should be obvious.

Note that I’m not rubber stamping the AGS Ideal-0 cut grade. I think that the proportions parameters are too broad, and I’ve seen a lot of ASET images that give me pause. Sometimes I stare at the ASET image provided and wonder how that diamond possibly qualified as an ideal cut diamond. I’m not alone on this… Sometimes I shoot a copy of the lab report over to friends of mine who share my insane passion for truly well cut diamonds and ask for their opinion. They usually shoot back a response expressing their frustration with the ever-expanding range for what is deemed to be ideal cut theres

GIA Excellent Cut: It is questionable whether diamonds with an overall cut grade should be referred to as ideal cut diamonds. The majority of diamond dealers who I’ve spoken with who prefer the grading platform of the AGS Laboratory do not consider GIA Excellent cut diamonds to be comparable. They adamantly reject the idea of referring GIA Excellent cut diamonds as ideal cut. They simple refer to them as GIA Excellent cut diamonds.

The fact of the matter is that a lot of diamonds graded as GIA Excellent would not receive an overall cut grade of AGS Ideal-0 if they were submitted to the AGS Laboratory. The stumbling block that trips up a lot of diamonds is the ASET scan. Plus the proportions parameters adhered to by the AGS Laboratory is a bit tighter than those relied upon by the GIA. Then there is the fact that the GIA rounds off some of the measurements provided on their diamond grading report, while the AGS does not.

I do not feel that this necessarily eliminates GIA Excellent cut diamonds from the ideal cut classification. The standards for polish and symmetry are comparable, and there are a lot of GIA graded diamonds with the proportions outlined above. The problem is that the GIA rounds off some of the measurements provided on their diamond grading reports. Thus in order to know the proportions for certain, you’d need to obtain a manufacturers Sarin | OGI | Helium report. Unfortunately the majority of online dealers and retail jewelers will not be able to provide you with more than the basic version of the report. That version of the report is essentially useless.

If I were considering ideal cut diamonds graded by the GIA, then I would only consider options with an overall cut grade of GIA Excellent and proportions within the range outlined above. I wouldn’t even consider anything cut with broader proportions. I’d want to see images of the diamond as seen through an ASET Scope, a Hearts and Arrows Scope, and and Ideal Scope. And I mean actual images, actual photographs, not the picture perfect computer generated renderings that I see popping up all over the place! Those are not accurate representations of the diamond! They are based solely upon the proportions, and those can be manipulated to improve image quality.

EGL Tolkowsky Cut: Generally not be ideal cut diamonds by my standards. Not only is the range of proportions that they adhere to well beyond the range defined by Marcel Tolkowsky’s Diamond Design, but there is a lot of debate about whether the grading standards of this laboratory are even close to being accurate. The RapNet Diamond Exchange Banned EGL Graded Diamonds in October of 2014. And there is a series of class action lawsuits that have been filed against jewelers who sold EGL graded diamonds. The claim being that the diamonds were mis-represented due to being over-graded. Several of the jewelers being targeted by this lawsuit refer to it as extortion. We’ll leave that for the courts to decide.

60 60 Ideal Cut Diamonds MythThe 60/60 Ideal Cut Diamond: The mythical unicorn is explored in great detail here. The belief that a diamond is ideal cut simply because it has a 60% table diameter and a 60% total depth is patently absurd. So called diamond experts who promote the idea of the 60/60 ideal cut diamond say that the crown and pavilion sections of a diamond will (somehow magically) properly proportioned if the table diameter and total depth are both 60%. This is just plain stupid. The fact of the matter is that I’ve seen there are a wide range of crown heights and pavilion depths.

Proving my point is as simple as conducting a search for AGS Ideal Cut Diamonds and GIA Excellent cut diamonds with a total depth and table diameter of 60% and then running through the options presented.

This GIA Excellent cut diamond has a total depth and table diameter of 60% and thus it falls into the classification of what is commonly referred to as the 60 / 60 ideal cut diamond. Technically I suppose that statement is accurate, since a diamond with these proportions does fall within the ideal cut range designated on the 2012 AGS proportions guidelines for diamonds with a 60% table diameter. But that doesn’t really make the diamond Ideal Cut by my standards.

Does this photograph of the diamond show a pattern of light return which is evenly distributed throughout the diamond? Does light appear to be reflecting evenly off the facets? Does the diamond exhibit excellent contrast brilliance? The answer to all those questions is no. The crown angle is too shallow and the pavilion angle is too steep. A pavilion depth of 43.5% happens to be the critical tipping point where light begins not to strike fully off the pavilion facets.

The pavilion depth of this diamond is 44.5% which is one full percent past that point. Clearly the crown and pavilion sections of a diamond will not automatically be correct, simply because the diamond has a total depth and table diameter of 60%. So much for the ideal of 60/60 ideal cut diamonds. Just like every other diamond cut in the world, it is a matter of finding one with the right proportions. I can tell you from experience, it’s like looking for the infamous needle in a haystack. The odds of finding ideal cut diamonds that fall within the range of parameters outlined above is significantly higher.

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Obviously there is a lot to know about buying a diamond. I hope that the information contained in this ideal cut diamonds buying guide was helpful. I’d like you to know that you’re not alone on this journey. I’m happy to assist you with your search and answer any questions that you might have. Feel free to take advantage of my Diamond Concierge Service. There is no charge for this service. I’m compensated for my time via affiliate agreements with various vendors online. This does not affect your price on the diamond. The price on the diamond will be the same whether you find it on your own, or I locate it for you. I also don’t care whether you happen to be working with one of the companies I’m affiliated with, or buying from another online dealer or local jewelry store. It all comes out in the wash as they say…