Jewelry – Gem
Reexamination Certificate
2002-05-31
2004-06-08
Sandy, Robert J. (Department: 3677)
Jewelry
Gem
Reexamination Certificate
active
06745596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to faceted gemstone construction and, specifically, to the faceted construction of a princess cut diamond, where said faceted construction provides improved luster and appearance.
2. Description of the Related Art
Diamonds have fascinated and beguiled mankind for thousands of years, yet the exact history of the precious stone is unknown. The word “diamond” is derived from an ancient Greek verb meaning “I tame” or “I subdue”. The ancient Greeks used this word for the hardest substance known, but it is difficult to tell what that substance was at that point in time—some believe the ancient Greeks may have been referring to the second hardest mineral, corundum (the gem variety of corundum is sapphire). Tracing the history of diamonds is complicated by this ambiguity with names.
The first diamonds were probably discovered around 800 BCE in riverbeds in India, and these alluvial deposits were rich enough to supply most of the world's supply until the eighteenth century, when India's dwindling supply probably spurred the exploration that led to the discovery of diamonds in Brazil, which became the next most important diamond source. In 1866, South Africa's massive diamond deposits were discovered, and a world-wide diamond rush was on. Currently, western Canada is the site of the world's newest diamond rush.
The cutting of diamonds into the complex formatted shapes we now associate with gems is a relatively recent practice. Although polishing and grinding with diamond dust was known from the thirteenth century, the first reference to diamond cutting is in 1550 in Antwerp, the most important diamond center of the period. Before the 1900's, the various shaped cuts of diamonds, such as the Table Cut, the Old Single Cut, the Rose Cut, and the European or Old Mine cut, varied widely in appearance. Because of the limitations of technology, these diamonds had very small tables, large culets, and short pavilion facets (definitions of these below); but there was no single widely-recognized or agreed-upon standard of cutting them. Until recently, a unified science and theory of facet proportion did not truly exist.
In 1919, diamond cutter Marcel Tolkowsky wrote a doctoral dissertation that essentially established the modern standard of a “brilliant-cut” diamond. Using only his own visual assessments of different variations of diamond cuts, Tolkowsky posited a theory of what cutting angles would produce the most proportionate balance of brilliance, scintillation, and dispersion in a gem-quality diamond. His measurements for achieving this balance were exact and strict. Fortuitously, improved cutting techniques and technology were being developed at the same time that finally allowed cutters to achieve more precise and stream-lined designs. Since that time, Tolkowsky's measurements have evolved into the looser “Ideal Cut” standard promulgated by the American Gem Society (AGS).
The round brilliant-cut diamond sets the standard for all other diamond shapes, and accounts for more than 75% of diamonds sold today. The “Ideal Cut” brilliant-cut diamond has 58 facets (or 57, if there is no culet), which are broken down as shown in
FIGS. 1A
(side view),
1
B (top view), and
1
C (bottom view). The terminology used for describing the parts of the brilliant-cut diamond is used for describing the basic components of all the cuts of diamonds.
As shown in the brilliant-cut diamond profile of
FIG. 1A
, there are three basic sections to a diamond: the crown
110
, the girdle
120
, and the pavilion
130
. The girdle
120
is the narrow rim of the gemstone that separates the crown
110
from the pavilion
130
. It is the section with the largest diameter of any part of the stone. Usually it is left in an unpolished state with a matte finish. However, to achieve more overall brilliance (described below), girdle
120
is often ground. Crown
110
and pavilion
130
can be understood as the “top” and “bottom”, respectively, of the brilliant-cut diamond. The tiny facet on the pointed bottom of pavilion
130
is the culet
135
. The large, flat top facet of crown
110
is the table
115
.
As shown in the top view of
FIG. 1B
, the brilliant-cut diamond has 16 Upper Girdle facets
111
, 8 Star facets
112
, 8 Bezel facets
113
, and 1 Table facet
115
in the crown
110
, which totals 33 crown facets in all. As shown in the bottom view of
FIG. 1C
, the brilliant-cut diamond has 16 Lower Girdle facets
131
, 8 Main Pavilion facets
132
, and 1 culet
135
in the pavilion
130
, which totals 24 pavilion facets in all. The culet
135
is merely the point at the bottom tip of pavilion
130
, although the culet may sometimes be much larger. As seen from
FIGS. 1A
,
1
B, and
1
C, as well as Tables 1A and 1B below, the brilliant-cut diamond has 58 facets. These facets are further described in Tables 1A and 1B by the angle each of their flat planar surfaces form with a the horizontal plane of girdle
120
.
TABLE 1A
Brilliant-Cut Diamond Crown Facets
Ref. No.
Facet
Shape
Number
Angle
111
Upper Girdle
Triangle
16
~32.2° to 36.8°
112
Star
Triangle
8
~32.2° to 36.8°
113
Bezel
Kite
8
~32.2° to 36.8°
115
Table
8-sided polygon
1
0°
TABLE 1B
Brilliant-Cut Diamond Pavilion Facets
Ref. No.
Facet
Shape
Number
Angle
131
Lower Girdle
Triangle
16
~40.5° to 41°
132
Main Pavilion
Kite
8
~40.5° to 41°
135
Culet
Point
1
~98.5°
There are certain dimensional characteristics of a any gemstone that are useful for ascertaining its overall value. Many of these characteristics are based in the proportions the various parts of the gemstone have to the overall width of the gemstone. Using the brilliant-cut diamond in
FIG. 1A
as an example, the crown height (or crown height percentage) is calculated by dividing the height of the crown
150
by the overall width
160
of the diamond. The table percentage (or table) is calculated by dividing the table's width
170
by the overall width
160
of the diamond. A table that is too large or too small will reduce the overall dispersion of a diamond's brilliance (these qualities will be described below). The depth percentage (or depth) is calculated as the ratio of the overall depth
180
of the diamond by the overall width
160
of the diamond. A depth that is too shallow or too deep will allow light to escape through the bottom of the stone, reducing the stone's overall brilliance and dispersion.
These various characteristics will be defined and described differently, depending on the type and shape of the stone being discussed. For example, the “Ideal Cut” characteristics of a brilliant-cut diamond are listed in Table 1C below.
TABLE 1C
Brilliant-Cut Diamond Dimensions
Name
Dimensions
Value
Crown Height
Percentage of crown's height to the
~15%-16.2%
(Percentage)
overall width of the diamond
Table Percentage
Percentage of table's width to the
~52.4%-57.5%
overall width of the diamond
Depth Percentage
Ratio of the overall depth of the
~59%-63%
diamond to the overall width of
the diamond
The features that describe the optical beauty of a diamond are: brilliance, dispersion, and scintillation. For a cut diamond, a feature of primary importance is its brilliance, which is essentially how much it shines. A diamond has a refractive index of 2.42, which is a very high value compared with that of other jewels (the index of crystal is 1.55; rubies and sapphires, 1.77). As a result (using the brilliant-cut diamond of
FIG. 1A
as an example), when rays of light incident on table
115
reach pavilion
130
, most of the rays are reflected totally (i.e., the rays of light do not escape the diamond through pavilion
130
, but are reflected inward again), and escape upon reaching crown
110
, thereby reaching the observer's eyes as brilliance. The angles
131
,
132
, and
135
of pavilion
130
are important to total reflection, and thusly is important to the brilliance of a diamond.
The refractive index of the diamond also gives rise to the dispersion of the tota
Cohen & Pontani, Lieberman & Pavane
Samuel Aaron, Inc.
Sandy Robert J.
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