The ideal cut: A consumer's guide

Everyone's talking about it, and the facts are getting muddled. Here's the straight dope!

Is there a platonic form for cutting a diamond, one set of proportions and angles that consistently produces the best possible results? In the last few years, a particular package of diamond proportions for the round brilliant called the "Ideal cut" has become very popular. The modern Ideal cut is based on the 1919 doctoral dissertation of diamond cutter Marcel Tolkowsky. Tolkowsky, using a two-dimensional model of a diamond, calculated that the best possible balance of brilliance and dispersion would result from a 53 percent table, 16.2 percent crown height, a 43.1 percent pavilion depth, no culet, and a knife-edge girdle.

These proportions used to be taught in United States gemological courses as the standard, and cuts deviating too far from the Ideal were penalized by appraisers. But the Ideal cut fell out of favor over the years proposed because it generally is uneconomical to cut and appears smaller than a standard cut diamond of the same weight. An Ideal cut diamond costs more than a standard cut and not everyone was convinced it was worth it.

But in the past few years, three important factors led to a revival of interest in the Ideal cut:
1) better technology to measure diamonds
2) a respected new lab that grades cut
3) the popularity of symmetry viewers

New Technology
The invention of quick and accurate diamond measuring instruments called Sarin Machines, which can give an instant readout on proportions, have made it easier and quicker to cut to precise proportions. Sarin also makes a countertop machine that prints out instant measurements: a diamond's vital stats. The machine-generated numbers seem official, but be aware that the machine's operator decides what proportions will be called "Ideal," and sets the machine accordingly.

A New Cut Grade
A new diamond grading laboratory was opened in 1996 by a prestigious association of retail jewelers called the American Gem Society. The members of AGS, who are all gemologists, have over the years been the strongest supporters of Ideal cuts. Because it was difficult to convince consumers to pay a premium for these proportions without independent confirmation, the association decided it would sponsor a lab to provide that documentation. The AGS Gem Lab's Diamond Quality Document overnight became the only documentation that mattered when it came to cut. The AGS lab uses a 0-10 grading scale, 0 being best. The AGS zero is now synonymous with the Ideal cut.

But the AGS 0 grade doesn't just address a diamond's proportions: it also means the diamond has excellent symmetry and polish. No machine can measure the quality of a diamondıs finish.

The Symmetry Viewer
The third factor that has contributed to the growth of appreciation for Ideal cut diamonds is a diamond viewing device called the Firescope, which directs a thin beam of red light into a diamond, creating a pattern of reflections off its facets. With the Firescope, a diamond's symmetry can easily be seen with a glance. When a diamond is cut perfectly symmetrically to slightly modified Ideal proportions, a pattern of eight arrow shapes, almost a mandala, is visible in the Firescope when the diamond is in the face up position. When viewed from the pavilion, the diamond will show eight hearts. The romantic association with cupid is irresistable and many people would no doubt buy these diamonds for the hidden message alone.

Does the pattern seen in a Firescope correspond with excellence in cutting? Many people in the industry feel that it does. It clearly demonstrates symmetry, and areas of the diamond where light is leaking out rather than reflecting back show up as dark shapes.

To show a perfect pattern in a Firescope or other symmetry viewer, a diamond is cut to a standard similar to, but not identical to, the traditional Ideal cut. Sometimes in order to display the pattern, the proportion must be tailored to the way an individual stone handles light. Does that make a stone less "Ideal"? It depends on whom you ask. Diamonds cut to display this pattern, sometimes referred to as "hearts and arrows" or "super Ideals" became the standard in Japan during its boom years. No doubt their growing popularity in recent years in the United States has much to do with the fact that suppliers needed to find a new market after the economy in Japan started to slow down.

The Plot Thickens
In the diamond world, the Gemological Institute of America is Merrill Lynch: when they speak, everyone listens. A GIA report is an essential accompaniment to any important diamond sale. But the GIA Gem Trade Laboratory does not grade cut.

And they are not likely to grade cut anytime soon: GIA president Bill Boyajian went out of his way in a recent editorial in GIA's gemological journal to say that there was no such thing as an Ideal cut and that the term should not be used.

He was writing in response to part one of a GIA study of how a diamond handles light. Part one, which addressed brilliance only, used a computer model of a diamond to measure light in virtual diamonds of different proportions. The study said that there were many sets of diamond proportions that performed well in returning light back to the eye. The Ideal cut was among them but not at the top of the list. So does that mean the Ideal cut is falling from favor? Well, not exactly, its supporters argue. GIA's study only measured brilliance, not dispersion. The proponents of the Ideal cut have never claimed that it was the most brilliant, but that it had the best balance of brilliance and dispersion. And the "best balance" is in the end an aesthetic judgement. And the GIA study does not disprove that an Ideal cut diamond is a beautiful diamond.

The Bottom Line
So what is a diamond buyer to do when experts disagree? A few things to remember:

1) It's the relation between table size, crown angle and pavilion depth that matters more than the measurements themselves. A diamond can fall within the accepted ranges for Ideal proportions and still not deliver light the way a well cut stone does. Don't look so hard at the numbers that you forget the whole point is the way the diamond handles light, creating beauty. The human eye is a pretty sophisticated measuring device too. At Alrashid Cyber Mall, we spend a lot of time looking at diamonds. When we see a stone that is exceptionally well cut, that sparkles with brilliance, we flag it in our database as a Alrashid Cyber Mall Top Selection. Many of these diamonds don't have strict Ideal proportions but they all handle light exceptionally well.

2) Symmetry and polish are just as important as proportions. In fact, some of the best deals in the market today are what are known as "double very goods," diamonds that the GIA has graded very good to excellent for both symmetry and polish. The quality of the finish of a diamond is a good indication of the level of care that has been taken in its craftsmanship.

3) The only "AGS 0" that matters is on an AGS report. Sarin machines can be set to print out a document that measures whether a stone conforms to Ideal proportions but tolerances are set by the user. And Sarin machines cannot measure the all-important symmetry and polish.

4) Ideal cuts are beautiful diamonds, no question. And with an AGS zero cut grade, you are assured that you are buying a well-cut and well crafted diamond. But Ideal cuts are not only more expensive because of the sacrifice of weight required to cut them, they also look smaller than a standard cut diamond. The proportions are tall and skinny, so less of the weight goes into diameter, which is how most visually judge size. For this reason, many people prefer well-cut stones that are wider. One such proportion is known as 60/60, but remember, just as with the Ideal cut, it is the relation of angles and proportions that matters, not any one number in itself.

5) Do what you need to do to make yourself feel confident. Does your stock portfolio contain Microsoft and AT&T? Go for an AGS zero, the blue chip of the cuts. If you feel confident enough to make your own choice--if you are a NASDAQ IPO kind of guy--you might find a well cut diamond without the label or paper that may be equally beautiful. Just don't scrimp on polish and symmetry!

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