Cowing Talk Highlights Ideal Cut ‘Sweet Spot’

JCK gemstone editor Gary Roskin, playing Boswell to Michael Cowing’s Johnson, presented a seminar on Thursday titled “Looking for Beauty: Perspectives of Michael Cowing,” during which he said, “Michael Cowing could very well be the next Marcel Tolkowsky.”

Cowing, a small independent jeweler, appraiser, gemologist, and gem cutter based outside Annapolis, Md., who also has a research and development engineering degree and is educated in computer science, plays devil’s advocate in the world of cut grading. In an article titled “Describing Diamond Beauty: Assessing the Optical Performance of a Diamond” in the January/April 2000 issue of Journal of Gemmology, Cowing focused on simplifying for the jewelry industry and the consumer the science and understanding of a diamond cut’s “light performance” and its resulting beauty.

“In the round brilliant cut, the finest cut quality or ‘make’ brings out the best in the attributes of diamond beauty,” writes Cowing. “Those three attributes are brilliance, fire, and sparkle.” But the labs are more focused on the numbers—the proportions that affect the beauty attributes.

“In tennis,” says Cowing, “the best athletes use a racket with the largest sweet spot and aim to hit its center. In diamond design, the evolution of the Ideal has led cutters to that center of the largest sweet spot in round-brilliant diamond cutting. The cutter’s sweet spot is that range of diamond proportions and angles having the best optical performance and beauty.”

The factors that characterize the contrast quality of brilliance are the sharpness, number, sizes, and uniformity of the distribution of the diamond’s mosaic-appearing pattern of reflections.

“Every diamond has dispersion,” says Cowing. “It’s a mineralogical property. But not every diamond has fire. It is the quality of the cutting—and the right contrasting illumination that brings out the fire.”

Cowing defines scintillation as “the diamond’s sparkle, occasioned by movement of either the diamond, the illumination, or the observer. This quality of light return is the sharp, on-off, bright-dark sparkle or flashes of light ‘dancing’ from the crown of the diamond.”

The Numbers

Because of the historical overemphasis on Tolkowsky’s theoretical pavilion and crown angles of 40.75 degrees and 34.5 degrees in association with “Ideal,” it is important to know that the five diamonds that Tolkowsky listed in his book as examples of maximally brilliant diamonds had pavilion angles from 40 degrees to 41 degrees, and crown angles from 33 degrees to 35 degrees. Additionally, Tolkowsky notes in his book that American writers credit Henry D. Morse with first cutting for “maximum brilliancy.” Morse used 41 degrees and 35 degrees for his ideal cut.

Differences of opinion between GIA and AGS principally concern the amount of variation in angles and proportions from those of Morse and Tolkowsky that retain ideal brilliance, fire, and sparkle. The chart of GIA cut grade estimation for the 56 percent table shows that the “sweet spot” of potentially excellent combinations of crown and pavilion angles has as its center a pavilion main angle of 41.2 degrees and a crown main angle of 34 degrees. Again, Tolkowsky angles are 40.75 degrees and 34.5 degrees and the Morse angles are 41 degrees and 35 degrees.

The AGS cut grade estimation for a 56 percent table shows that the “sweet spot” of potential AGS 0 and 1 combinations of crown and pavilion angles has as its center a pavilion main angle of 41.1 degrees and a crown main angle of 33.75 degrees.

Why is this important? What do our eyes see with these angles? They should see beauty—a great combination of brilliance, fire, and sparkle.

“In the late 19th century, the pavilion was predominantly pavilion main facets,” says Cowing. “These are the facets not only responsible for returning light—or brilliance—but also for big flashes of color—the fire of the diamond.”

But during the 20th century the pavilion mains got skinnier, and therefore showed more lower halves, increasing scintillation. However, the decrease in the size of the mains meant less fire.

Cowing says, “An attractive balance between the pavilion mains and halves is necessary for the ideal cut to retain, on one hand, the large flash sparkle and fire that was the hallmark of the early ideal, and on the other hand, benefit from the greater scintillation of the modern round brilliant.” This is exactly what you get inside the sweet spot. In the end, says Cowing, “the worth of a measure of diamond beauty depends upon how well it agrees with human judgment. Perception of beauty is everything.” For more information on judging beauty in a diamond, visit Cowing’s Web site at www.acagemlab.com.