Great question, you'd think there would be a quick and easy answer. But, no.
The term "ideal" has often been used to describe only the best cut diamonds, but it’s also been confused and abused over the years. After 300 years of experimentation and refinement, experts now agree that there's more than one simple way to describe the cut of a round brilliant diamond.
Although he never used the word "ideal" in his proof of Diamond Design (1919), Marcel Tolkowsky argued that a very tight range of proportions – based on Table Percentage = 53%, Crown Angles = 34.5 degrees, and Pavilion Angles = 40.75 degrees – produces optimal fire and brilliance in a finished gem diamond. Like most basic mathematics and physics, his numbers have withstood the test of time. They still hit the "sweet-spot" of most modern ideal standards.
After teaching 1000’s of gemologists about these “ideal” proportions over many years, the Gemological Institute of America (GIA) did not issue proportion-based cut grades on their diamond reports. However, they did recently introduce a performance-based grading system for cut that defines five levels of cut quality - Excellent, Very Good, Good, Fair, and Poor - with the top two grades being the most prevalent.
For the past decade, the American Gem Society (AGS) has pioneered and strongly endorsed the use of “ideal” in conjunction with a consumer-friendly numeric scale of 0 - 10 (with “0” being Ideal) to quantify multiple factors affecting cutting quality. Their Zero Ideal Cut Grade is based on an overall combination of ideal light performance, ideal proportions, and ideal finish – which includes ideal polish and ideal symmetry. This top grade represents just 3% of round diamonds in the marketplace.
There are diamonds that also exhibit extra “ideals" when viewed in various viewing devices. Some show ideal patterns of optical symmetry when you view diamonds directly under specialized filters and lighting environments. Others generate ideal computer-generated numbers, scales, images and guides that compare one "virtual" diamond with another.
But, diamond reports and viewing devices will only ever tell you so much. In the final analysis, I always recommend looking at any diamond you may consider owning. That’s what all the experts I've ever met do.
Why? Because, diamonds are dynamic 3-D works of art! They express their beauty in motion. Their true nature and appeal is impossible to reveal with a mere snapshot. It should not come as a big surprise to find that they often look very different in reality than they do “on paper”.
Monday, April 23, 2007
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6 comments:
Marteen...
Thanks for clarifying the overused (and often abused) diamond term "ideal cut". Ideal cut diamonds are reminiscent of beautiful women; one could be chosen based upon measurements (proportions, percentages, etc.), color (of hair, eyes, etc.), clarity (of thinking, skin, etc.) and the like... but what cannot be measured in life (or in a diamond grading report) is that special "eye connection" that occurs between two individuals. This is the real "sweet spot", and few understand it better than a diamond cutter! Thanks again!
What is an ideal depth/table for a princess cut diamond?
The princess cut has until recently been a generic style. However, the AGS has just published the first "ideal" performance charts for different configurations of princess cuts that include a variety of depth/table ratios, you can contact them through the Wiz's Favorite Links - American Gem Society (AGS).
Maarten, you could not be more correct! My husband and I bought a hearts of fire milgrain cathedral wedding set in Belize City, with a dazzlingly beautiful .77 center stone. While this stone is an I1, it way out-sparkles and actually LOOKS larger than a 1.12 carat VVS1 diamond I already have that cost substantially more! This is the first time I have had people NOTICE a ring and comment on it.
Is the new AGS 0 Ideal report based on firescope or idealscope
And does AGS comment on light leakage?
How do you feel about eightstar diamonds? I understand you used to work with them a long time ago.
Thanks
Hi Casey,
The new AGS Zero Report is not based on the Firescope or the Idealscope. It is based on the ASET (Angular Spectrum Analysis Tool) which is a highly refined and more comprehensive version of both these earlier tools.
I've always said that seeing beauty in diamonds isn't rocket science, but it is necessary to understand brightness, fire and sparkle - not simply "100% light return" (whatever that means).
It is no longer sufficient to report whether or not light "leaks" through a diamond. It is far more important to know where and how the diamond derives its light and how intensely it is returned to the viewer's eye.
For this reason the AGS also uses both forward and reverse light ray tracing technology to analyze fire, and dynamic modelling to analyze scintillation.
AGS analyzes 3 separate categories with a total of 11 distinct factors in its Zero Ideal Cut grade. Light performance is subdivided into brightness, dispersion, leakage and contrast. Proportion factors include tilt, durability, weight ratio, culet size and girdle thickness. Finish includes polish and symmetry. It is the most robust and thorough methodology that I know of that's in use today.
And finally, yes I used to work with EightStar. The operative words are "used to". I believe that action speaks louder than words.
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