Category Archives: Ideal Cut Diamonds

Ideal Cut Diamonds – What is it all about?


“The notion that there’s something special about one set of proportions which is not produced by another set, just doesn’t hold up.” Dr. Mary Johnson, Manager of GIA Research and Development in Carlsbad, CA.

Hi again,

The issue of “Ideal Cut” diamonds is a complicated one and one which the average consumer can focus on to the exclusion of other factors in a diamond which are really much more important.  To put it simply, the phrase “ideal cut” refers to a set of statistics to which a diamond is cut and implies that this set of statistics produces the best looking diamond. As you read on, you will begin to understand why, instead of focusing on the term “ideal,” you should be letting your EYES speak to you. You should be looking at the diamond itself and not just its statistics. At A. Fishman & Son, we focus on offering our customers “well cut” diamonds that are pretty and reflect full brilliance and fire.

What do we mean by “well-cut” and how do we distinguish our cut from “ideal” cut (or “ultra ideal”) diamonds?  While we own and offer many diamonds which have proportions which would be considered “ideal” cut, they are all very fine cut diamonds.  However, unlike our diamonds which fall within the “ideal cut” proportions, there are many diamonds which fall within those “numbers” but whose cut is in fact poor and those diamonds are not pretty diamonds.  Like the Gemological Institute of America (“GIA”) (see below), we do not feel it is appropriate to use the term “ideal,” as it reflects the concept of “perfect.”  And we do not believe that all diamonds which fall within the “ideal” cut proportions deserve the connotation that the term implies.

Ideal Cut

An “ideal” cut diamond refers to a round diamond cut to a specific set of cutting guidelines that delineate the proportions that are assumed to give a round diamond the greatest amount of fire and brilliance.  There is a tremendous amount of information, some good and some very misleading, regarding what an “ideal” cut diamond should look like and what proportions it should be cut to.

One of my biggest issues with the concept of “ideal” cuts is this. If an “ideal” cut diamond reflects a single set of cutting proportions which are “perfect,” how is it that the depth and table percentages can have such a wide range?  The traditional proportions often quoted for ideal cut – and “established” by the American Gem Society (“AGS“) is a table percentage of 52.4-57.5% and a depth percentage of 58.4-62.9%.  This set of proportions assumes that any two diamonds whose proportions are cut within these ranges is equally pretty and look alike.  Is this really possible?  Is it possible that two diamonds which fall within this range, but at the extremes, really look the same?  In our opinion, and the opinion of the GIA, this is patently false.  A diamond of 60% depth and 57% table may be a pretty diamond, but, in our opinion, a diamond of 62.9 depth and 53 table is not.  And it is obvious to any one who thinks through the issue that these two diamond will not look the same to the eye.

GIA Research and Conclusions

Recently, the GIA has undertaken research to determine whether the noted cutting proportions of “ideal” cut stones actually produce the maximum fire and brilliance in a round diamond compared to other cutting proportions.

In the Fall 1998 Issue of the GIA’s Gems and Gemology, the GIA published the first of its articles regarding cut in its landmark The synopsis of this article states in relevant part:

“The results of this study suggest that there are many combinations of proportions with equal or higher WLR (weighted light return) than the traditional ‘Ideal’ cuts. In addition, they do not support analyzing cut by examining each proportion parameter independently.”

In fact, the research in this case showed that round diamonds with larger tables (64-66%) and with shallower crown and pavilion angles (not the 35.8 degrees on the crown and the 43 degrees on the pavilion often mentioned), delivered MORE light return than traditional “ideal” cut proportions.

In an editorial in the same issue (see Demystifying Diamond Cut) the President of the GIA, William E. Boyajian, made a very important statement regarding the use of the term “ideal cut.”  He stated:

“We also know that there are many combinations of proportions that yield equally attractive round-brilliant-cut diamonds. In fact, we know that diamonds can be cut in a fairly wide range of proportions to yield the same high light return, which can lead to better utilization of the rough and a better fit with the myriad tastes that exist in the global marketplace.

Finally, we know from our extensive historical research on cut that there have been numerous claims to a single set of ‘Ideal’ proportions in round-brilliant-cut diamonds. The derivation and use of the term ‘Ideal’ is thus confusing at best, but not unlike that of ‘blue-white’ and ‘perfect’ decades ago. Although it is not GIA’s role to discredit the concept of an ‘Ideal’ cut, on the basis of our research to date we cannot recommend its use in modern times.” (emphasis added)

In the Fall 2001 Issue of the GIA’s Gems and Gemology, the GIA published its second article regarding cut in its article Modeling the Appearance of the Round Brilliant Cut Diamond: An Analysis of Fire, and More About Brilliance. As Mr. Boyajian states in his editorial summarizing this article:
“The authors conclude that there is no easy way to characterize the “best” cut in round brilliants for either brilliance or fire. Rather, it is the complex interaction of multiple proportions, involving all of a diamond’s facets, that must be considered in the assessment of these key appearance aspects. Furthermore, there is now even more evidence to support the conclusion that there is no one “best” cut for a round brilliant diamond.” (emphasis added)

In the Spring 2002 issue of the GIA’s The Loupe, the GIA published an article entitled The Science of Cut. This article, following up on the two previously mentioned articles, confirms that there really is no single best cutting proportions for a round diamond.  This article states in relevant part:

“All of a diamond’s quality factors play a part in a polished round brilliant’s overall appearance, but the role proportions play in the quality of diamond cut has historically been the least understood….

Early on, researchers at GIA expected their results to corroborate one or more of the existing cut grading systems, but their work to-date indicates the underlying approaches of most existing systems are not substantiated by the data.

The industry has for decades embraced the concept that an extremely limited set of round brilliant diamond proportions produce maximum brilliance and fire so, in terms of an evaluation of cut, any deviation from this set of proportions would impact the appearance materially.  It believed that the further the proportions deviated from this limited set of proportions, the greater the impact was on the appearance of the diamond.

Preliminary findings of the GIA’s diamond cut research indicate otherwise...They discovered that there are many proportion combinations that can yield equally strong-performing diamonds…The notion that there’s something special about one set of proportions which is not produced by another set, just doesn’t hold up.” (emphasis added)

Finally, in the Fall 2004 Issue of the GIA’s Gems and Gemology, the GIA published its third article regarding cut in its article A Foundation for Grading the Overall Cut Quality of Round Brilliant Cut Diamonds. In this article, the author ties the various elements of the GIA’s studies together.  Some of the main findings from the GIA’s research discussed in the new article, as summarized in the GIA’s editorial, Unlocking the Secrets of the Fourth C are:

  • Proportions need to be considered in an interrelated manner.  The combination of proportions is more important than any individual proportion value.  Individual proportions must not be assessed on their own. It is the complex interrelationship of individual proportions that matters most in the face-up cut appearance and overall cut quality of a diamond.
  • There is no one set of proportions that yields the most beautiful diamond. Similarly, the long-held view that expanding deviations from a fixed, arbitrary set of proportion values produces diamonds with increasingly poorer appearances is simply not valid.
  • Attractive diamonds can be manufactured in wider range of proportions than would be suggested by historical practice or traditional trade perception.
  • Viewing environment plays an important role in diamond appearance — to be attractive, a diamond should look good in realistic environments.
  • Personal and international market preferences should be accounted for.  Diamonds with different appearances can be found within each cut grade, so individuals need to look at the diamond itself, not just the grade — to choose the one they like best.

What does all of this mean to you, the consumer?  It means that you need to rely on the expertise of a diamond source that understands what diamonds are all about, that can evaluate the merits of a diamond beyond the mere statistics that appear on a certificate, and that can guide you to the right diamond for you.  That diamond source has to have the experience which only time and generations of buying diamonds can give you.  After all, if you never have to put your own money down (like the hundreds of internet sites who simply collect nationally available diamond lists), how can one really understand which diamond is desirable and which one is not!Whew, that was a long discussion but very important.

So, in the meantime, until next time, Mind Your Diamonds!

Josh Fishman