Oh, patents! Wueste's brilliant-cut diamond

Copyright Françoise Herrmann

Robert J. Wueste's brilliant-cut diamond invention is recited in the lapsed US utility patent US6698239, titled Brilliant-cut diamond and method of forming thereof. 

The Wueste brilliant-cut diamond patent recites a varying number of facets. Per the abstract of the patent, the number of facets depends on how the facets are counted -- including or excluding the table;  in reference to the crown, or to both the pavilion and the crown.  Thus, for example, the brilliant-cut patent recites a preferred embodiment comprising a crown with 56 facets (excluding the table), and 114 facets including the pavilion. Whereas in another preferred embodiment, the patent recites a crown comprising with 64 facets (excluding the table) and 122 facets including the pavilion, per the following:

A brilliant-cut gemstone having a pavilion, a girdle, and crown is disclosed. The pavilion of the gemstone has 56 facets: specifically, 8 lower diamond-shaped facets, 16 middle kite-shaped facets, and 32 upper triangular facets. The girdle and table may be formed of one or more facets. In one preferred embodiment, the total number of crown facets (excluding the table) is 56, making a total of 114 facets (including the table). In another preferred embodiment, the total number of crown facets (excluding the table) is 64, making a total of 122 facets (including the table). [Abstract US6698239]

According to Wueste, the brilliant-cut sets the standard for diamond cuts, and accounts for 75% of diamonds sold worldwide. The brilliant-cut is also used for different sorts of gemstones, but it is specifically recited for diamonds in this patent.  

The patent discloses the significance of a diamond cut, which impacts the diamond’s appearance, giving it brilliance, fire and scintillation. Thus, the number of facets of a diamond is significant because facets can increase the brilliance of a diamond. The brilliance of a diamond is “how much it shines”. Brilliance is a function of the refractive index of diamonds, which is the highest of all gemstones, and of the geometry of the cut, which can maximize the amount of light reflected back out through the crown of the diamond, after it has entered the pavilion, through the table. Once light is reflected, it disperses into the seven rainbow colors of the visible light spectrum, resulting in what is called the fire of a diamond, also facilitated by the angle of the facets. Scintillation is the glittering effect of reflected light, when there is movement (of the diamond or the observer), in turn, a function of the size, cut, polish, and angle accuracy of the facets.

The theory of diamond optics, or of the impact of diamond cutting on the desirable characteristics of brilliance, fire and scintillation, is usually traced back to Marcel Tolkowsky’s Ideal Cut.  An Ideal Cut whose proportions were presented, in 1919, in a book titled Diamond Design:  A Study of the Reflection and Refraction of Light in a Diamond, itself part of Tolkowsky’s doctoral dissertation on diamond grinding, at the University of London. A book, which in turn would inform the American Gem Society (AGS) Standards for grading and evaluating diamonds, according to 4Cs: Cut, Color, Clarity and weight in Carats.

Notwithstanding the scientific optical foundation of diamond cutting, with explicit proportions and an Ideal Cut standard, diamond cutters are always striving to exceed the Tolkowsky-inspired AGS standards -- increasing the number of facets, and varying the angles at which the facets are cut, using new tools to streamline the process.  Robert J. Wueste’s brilliant-cut, as recited in US6698239, is no exception.  An ever more brilliant, scintillating and fiery diamond will always be needed.


The included extracted patent figures show a top view of the crown (fig. 3B) and a bottom view of the pavilion (fig. 2A) of one embodiment of Wueste's brilliant-cut diamond, together with the image of a brilliant-cut diamond. 

Reference

Tolkowsky, M. (1919) Diamond design: A Study of the Reflection and Refraction of Light in a Diamond.

http://www.folds.net/diamond_design/index.html