Cut design of diamond for ornamental use

Details Cut design of diamond for ornamental use Cut design of diamond for ornamental use

2001-06-12

2004-02-24

Chop, Andrea (Department: 3677)

Jewelry

Gem

CD11S089000, CD11S090000

Reexamination Certificate

active

06694778

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cut design of diamonds and jewelry, and more particularly to a novel cut design capable of providing diamonds and jewelry with brilliancy and scintillation excelling in both quality and quantity over conventional cut designs.
2. Description of the Related Art
In order to provide brilliant diamonds and jewelry by cutting diamonds for use in ornaments, diamonds for ornamental use in the brilliant cut having 58 facets each and jewelry using such diamonds have been obtained.
Four criteria used in evaluating diamonds, commonly known as 4C's, are as follows:
1. Carat (unit of weight);
2. Color;
3. Cut (proportion, symmetry and polish);
4. Clarity (quality and quantity of inclusions).
Regarding the weight expressed in carats, the value of a diamond has traditionally been determined by the size, which is measured by the weight. The color depends on the gemstone; colorless and transparent stones are scarce and highly valued. The Gemological Institute of America (GIA) assigns D, E and F grades to colorless and transparent diamonds, and incidentally yellowish, if only slightly, ones are graded K or even lower. Cut design gives brilliancy and scintillation to a gem. The relative clarity, determined by inherent impurities and/or flaws, is also determined at the raw stone stage.
Since the color and clarity are intrinsic to the gemstone, the only factor permitting artifice is the cut design, which determines brilliancy and scintillation. Therefore, studies have been continued to find cut designs which can enhance these attributes.
Mathematician Tolkowsky proposed what is known as the GIA system of cut design to increase the brilliancy and scintillation of diamonds. The ideal cut according to the GIA system has a pavilion angle of 40.75 degrees, a crown angle of 34.50 degrees and a table diameter corresponding to 53% of the girdle diameter. Essentially, a cut should be evaluated according to its contribution to beauty, but more importance tends to be attached to the yield from the gemstone.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a cut design which can further enhance the brilliancy and scintillation of diamonds.
Another object of the invention is to provide a cut design which, when a diamond so cut is radiated from a specific direction, results in extremely enhanced brilliancy and scintillation, the diamond in that cut design, when observed under light, permitting perception of the relative degree of its brilliancy and scintillation by the twinkling of the reflected light.
Still another object of the invention is to provide a cut design having a spectral effect, capable of causing lights coming into a diamond to separate into its spectral components in the diamond and to reflect bluish lights from table facets and crown facets.
Since the upper portion of a cut diamond from the girdle level is usually extruded over its setting and exposed to the illumination, directions of the emerging lights from the table facet and crown facets (including star facets, main facets and upper girdle facets) have important meaning among the lights derived from the incident ones on the table and crown facets. As a result of examining the directions of emerging lights, it has been found that lights emerging from crown facets are originated from incident lights both on the table facet and crown facets and lights emerging from the table facet are from the crown facets. The invention has been made from this discovery.
A cut design of diamonds for ornamental use according to the invention has a crown portion above and a pavilion portion underneath, permitting simultaneous observation of lights coming into crown facets and emitted from crown facets, lights coming into the table facet and emitted from crown facets, and lights coming into crown facets and emitted from the table facet, when viewed above the table facet of the diamond. To realize this feature, in the cut design according to the invention, the pavilion angle p ranges from 45 degrees to 37.5 degrees, and the crown angle c in degrees is within a range of satisfying the following equation:
−3.5×
p+
163.6≧
c≧−
3.8333×
p+
174.232.
The cut design of diamonds for ornamental use according to the invention comprises a crown having substantially a frustum shape and substantially a conic pavilion below the frustum portion. When the pavilion angle p ranges from 45 degrees to 37.5 degrees, and the crown angle c in degrees satisfies the following equation:
−3.5×
p+
163.6≧
c≧−
3.8333×
p+
174.232,
the cut design results that the angles between an incident light and an emitted light are substantially equal to each other among lights coming in the crown facets and emitted from crown facets, lights coming in the table facet and emitted from the crown facets, and lights coming in the crown facets and emitted from the table facet.
The diameter of the table facet in cut design of diamonds for ornamental use according to the invention is from 0.60 to 0.33 in its ratio to the diameter of the girdle, and more preferably should be between or equal to 0.55 and 0.38.
In the foregoing dimensional feature, it is preferable for the pavilion angle p to be between or equal to 45 degrees and 37.5 degrees and for the crown angle c in degrees to be within a range of satisfying the following equation:
−3.75427×
p+
172.8166≧
c≧−
3.74167×
p+
171.4883.
In order to make three focal angles coincide with each other in the wavelength range from violet lights to dark blue lights and to strengthen reflected bluish lights, it is preferable that the crown angle c in degrees is within a range of satisfying the equation of −3.7239×p+171.4315≧c≧−3.74167×p+171.4883. It is further preferable for the pavilion angle p to be not greater than 40 degrees.
In the cut design of diamonds for ornamental use according to the invention, the projection Gd (expressed in the ratio to the radius of girdle) of the distance from the central axis of the diamond to the culet side apex of lower girdle facets in the pavilion onto a plane, passing the girdle side apex of main facets in the pavilion and the central axis of the diamond, advisably should be not more than about 0.3. More preferably, it should be not more than 0.25, and a particularly preferable Gd value is around 0.2.
A diamond of a cut design having a pavilion angle and a crown angle conforming to the present invention has more powerful reflected light rays than any conventional cut design, and shines brilliantly as a whole. Furthermore, by reducing the table facet size and expanding the crown facet size, reflected lights from crown facets and incident lights on crown facets can be more effectively utilized, resulting in more effective diamonds for ornamental use.
When the angles between an incident light and an emitted light are substantially equal to each other among lights coming in the crown facets and emitted from the crown facets, lights coming in the table facet and emitted from the crown facets, and lights coming in the crown facets and emitted from the table facet, the reflected lights provide in intermittent shinning and diminishing directions. For this reason, as the direction of observation or the inclination of an axis of the diamond (the axis normal to the table facet) is varied while irradiating the diamond with light, angles at which reflected lights are powerful and angles at which reflected lights are weak bring about intermittently twinkling, and different intensities of brilliancy and scintillation are observed. This feature, together with powerful reflected lights, accentuates the brilliancy and scintillation of the diamond.
Furthermore, as the patterns of lights coming in and reflected by the diamond are finer, the glitter can be intensified. It is also made possible to separate the lights coming in the diamond into its spectral components, enabling the color q

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