Emerald-cut diamond method

Abstract

Emerald-cut diamond with length/width of 1.35 to 1.40; table of 55 to 60 percent; corner ratio of 13.5 to 14.5 percent; girdle thickness up to 3 percent; crown main angle of 28 to 45 degrees; first crown break angle of 2 to 6 degrees; second crown break angle of 2 to 6 degrees; pavilion main angle of 43 to 48 degrees; first pavilion break angle of 2 to 5 degrees; and second pavilion break angle of 2 to 5 degrees. Diamonds cut in accordance with these parameters may have light performance 0-grade domains on a grade map with wide crown and pavilion mains ranges. A method cuts the diamond according to the parameters, and may include selecting crown and pavilion main angles from the map, and cutting the diamond sufficiently close to the selected cutting parameters to obtain the light performance grade of 0.

Claims

1. A method for cutting an emerald-cut diamond to avoid excessive light performance deductions, comprising: a. cutting the diamond in a generally rectangular plan with a ratio of length to width, measured at a girdle between a crown and a pavilion of the diamond, of from 1.345 to 1.405; b. forming corners on the diamond; c. forming a table on the crown of the diamond having a width of from about 54.5 to 60.5 percent of the girdle width; d. forming a thickness of the girdle of up to 3.5 percent of the girdle width; e. forming a crown main facet tier adjacent the girdle having an angle with respect to the table plane of from 27.75 to 45.25 degrees (±0.25); f. forming a crown second tier facet adjacent the crown main facet tier having a first crown break angle between the crown main and second tiers from 2.5 to 5.5 degrees; g. forming a crown third tier facet adjacent the second crown tier facet having a second crown break angle between the crown second and third tiers from 2.5 to 6.5 degrees (±0.5); h. forming a pavilion main facet tier adjacent the girdle having an angle with respect to the table plane of from 42.75 to 48.25 degrees (±0.25); i. forming a pavilion second tier facet adjacent the pavilion main facet tier having a first pavilion break angle between the pavilion main and second tiers from 1.5 to 5.5 degrees; and j. forming a pavilion third tier facet adjacent the pavilion second tier facet having a second pavilion break angle between the pavilion second and third tiers from 1.5 to 5.5 degrees.

2. The method of claim 1, further comprising: selecting the ratio of length to width, the corner ratio, the table percentage, first and second crown break angles, first and second pavilion break angles, and ranges of the crown main angle and pavilion main angle corresponding to a grade map of light performance deductions for combinations of the crown and pavilion main angles over said ranges; selecting cutting parameters comprising crown and pavilion main angles from the grade map corresponding to a 0-grade domain; and cutting the diamond sufficiently close to the selected cutting parameters to obtain a light performance grade of 0.

3. The method of claim 2, wherein the grade map comprises a 0-grade domain density equal to or greater than 0.25.

4. The method of claim 3, wherein the 0-grade domain density is equal to or greater than 0.35.

5. The method of claim 2, wherein the emerald-cut diamond obtained has light performance deductions less than 0.50.

6. The method of claim 1, wherein the pavilion third tier is terminated at a culet.

7. The method of claim 6, wherein the first and second crown break angles are 3.5-4.5 and 2.5-3.5 degrees, respectively.

8. The method of claim 7, wherein the crown main angle is from 34.75 to 45.25 degrees.

9. The method of claim 8, wherein the first and second pavilion break angles are from 2.5 to 5.5 degrees.

10. The method of claim 9, wherein the first pavilion break angle is 2.5-3.5 degrees, wherein the second pavilion break angle is 3.5-4.5 or 4.5-5.5 degrees, and wherein the pavilion main angle is from 42.75 to 46.75 degrees.

11. The method of claim 10, further comprising: selecting the ratio of length to width, the corner ratio, the table percentage, first and second crown break angles, first and second pavilion break angles, and ranges of the crown main angle and pavilion main angle corresponding to a grade map of light performance deductions for combinations of the crown and pavilion main angles over said ranges; selecting cutting parameters comprising crown and pavilion main angles from the grade map corresponding to a 0-grade domain; and cutting the diamond sufficiently close to the selected cutting parameters to obtain a light performance grade of 0.

12. The method of claim 8, wherein the first and second pavilion break angles are 4.5-5.5 and 3.5-4.5 degrees, respectively, and wherein the pavilion main angle is from 43.25 to 48.25 degrees.

13. The method of claim 12, further comprising: selecting the ratio of length to width, the corner ratio, the table percentage, first and second crown break angles, first and second pavilion break angles, and ranges of the crown main angle and pavilion main angle corresponding to a grade map of light performance deductions for combinations of the crown and pavilion main angles over said ranges; selecting cutting parameters comprising crown and pavilion main angles from the grade map corresponding to a 0-grade domain; and cutting the diamond sufficiently close to the selected cutting parameters to obtain a light performance grade of 0.

14. The method of claim 9, wherein the first and second pavilion break angles are each 4.5-5.5 degrees, wherein the pavilion main angle is from 44.25 to 48.25.

15. The method of claim 14, further comprising: selecting the ratio of length to width, the corner ratio, the table percentage, first and second crown break angles, first and second pavilion break angles, and ranges of the crown main angle and pavilion main angle corresponding to a grade map of light performance deductions for combinations of the crown and pavilion main angles over said ranges; selecting cutting parameters comprising crown and pavilion main angles from the grade map corresponding to a 0-grade domain; and cutting the diamond sufficiently close to the selected cutting parameters to obtain a light performance grade of 0.

16. The method of claim 1, further comprising forming a pavilion fourth tier facet adjacent the pavilion third tier facet having a third pavilion break angle between the pavilion third and fourth tiers from 1.5 to 5.5 degrees (±0.5).

17. The method of claim 16, wherein the pavilion fourth tier is terminated at a culet.

18. The method of claim 17, wherein the first pavilion break angle is from 1.5 to 4.5 degrees, wherein the second pavilion break angle is from 1.5 to 4.5 degrees, and wherein the third pavilion break angle is from 1.5 to 4.5 degrees.

19. The method of claim 18, further comprising: selecting the ratio of length to width, the corner ratio, the table percentage, first and second crown break angles, first, second, and third pavilion break angles, and ranges of the crown main angle and pavilion main angle corresponding to a grade map of light performance deductions for combinations of the crown and pavilion main angles over said ranges; selecting cutting parameters comprising crown and pavilion main angles from the grade map corresponding to a 0-grade domain; and cutting the diamond sufficiently close to the selected cutting parameters to obtain a light performance grade of 0.

20. The method of claim 19, wherein the grade map comprises a 0-grade domain density equal to or greater than 0.50.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

(2) FIG. 1 is a top plan view of an emerald-cut diamond showing parameters according to an embodiment of the present invention.

(3) FIG. 2 is a bottom plan view of an emerald-cut diamond showing parameters according to an embodiment of the present invention.

(4) FIG. 3A is a side sectional view of an emerald-cut diamond as seen along the view lines 3-3 of FIGS. 1 and 2 showing parameters according to an embodiment of the present invention described in Example 4 below.

(5) FIG. 3B is a side sectional view of a four-tier pavilion, emerald-cut diamond according to an embodiment of the present invention described in Example 6 below.

(6) FIG. 4 is a map of the light performance grades of an emerald-cut diamond according to the “old time” parameters with an L/W ratio of 1.4, corner ratio of 0.14, a table % of 55, crown breaks of 5.5-2.5 and pavilion breaks of 11.5-4.5 over ranges of crown main angles of 39-41 and pavilion main angles of 11-5.

(7) FIG. 5 is an ASET image of the old time emerald-cut diamond of FIG. 4 for a crown main angle of 40 and a pavilion main angle of 53.5.

(8) FIG. 6 is a map of the light performance grades of an emerald-cut diamond according to the AGS Guidelines at [[https//www.]] cdn.ymaws.com/www.americangemsociety.org/resource/collection/BCC3840-BEFB-48B7-A29D-61E4068B85F6/lpt4_14.pdf for a diamond with an L/W ratio of 1.4, corner ratio of 0.14, a table % of 55, crown breaks of 7-7, and pavilion breaks of 11-7, over ranges of crown main angles of 35.5-46 and pavilion main angles of 43.5-56.5.

(9) FIG. 7 is a map of the light performance grades of an emerald-cut diamond according to the AGS Guidelines at [[https//www.]] cdn.ymaws.com/www.americangemsociety.org/resource/collection/SBCC3840-BEFB-48B7-A29D-61E4068B85F6/lpt4_14.pdf for a diamond with an L/W ratio of 1.4, corner ratio of 0.14, a table % of 60, crown breaks of 7-7 and pavilion breaks of 11.7 over ranges of crown main angles of 35.5-44 and pavilion main angles of 43.5-59.5.

(10) FIG. 8A is a map of the light performance grades of an emerald-cut diamond according to an embodiment of the present invention for a diamond with L/W ratio 1.35, corner ratio 14%, a table % of 55, crown breaks of 4-3 and pavilion breaks of 3-4 over ranges of crown main angles of 35.0-45.0 and pavilion main angles of 43.0-48.0.

(11) FIG. 8B is a chart of ASET images for the emerald-cut diamonds of FIG. 8A.

(12) FIG. 9A is a map of the light performance grades of an emerald-cut diamond according to an embodiment of the present invention for a diamond with L/W ratio 1.35, corner ratio 14%, a table % of 55, crown breaks of 4-3 and pavilion breaks of 3-5 over ranges of crown main angles of 35.0.45.0 and pavilion main angles of 43.0-48.0.

(13) FIG. 9B is a chart of ASET images for the emerald-cut diamonds of FIG. 9A.

(14) FIG. 10A is a map of the light performance grades of an emerald-cut diamond according to an embodiment of the present invention for a diamond with L/W ratio 1.35, corner ratio 14%, a table % of 55, crown breaks of 4-3 and pavilion breaks of 4.5 over ranges of crown main angles of 35.0-45.0 and pavilion main angles of 43.0-48.0.

(15) FIG. 10B is a chart of ASET images for the emerald-cut diamonds of FIG. 10A.

(16) FIG. 11A is a map of the light performance grades of an emerald-cut diamond according to an embodiment of the present invention for a diamond with L/W ratio 1.35, corner ratio 14%, a table % of 55, crown breaks of 4-3 and pavilion breaks of 5-4 over ranges of crown main angles of 35.0.45.0 and pavilion main angles of 43.0-48.0.

(17) FIG. 11B is a chart of ASET images for the emerald-cut diamonds of FIG. 11A.

(18) FIG. 12A is a map of the light performance grades of an emerald-cut diamond according to an embodiment of the present invention for a diamond with L/W ratio 1.35, corner ratio 14%, a table % of 55, crown breaks of 4-3 and pavilion breaks of 5-5 over ranges of crown main angles of 35.045.0 and pavilion main angles of 43.0-48.0.

(19) FIG. 12B is a chart of ASET images for the emerald-cut diamonds of FIG. 12A.

(20) FIG. 13 is a map of the light performance grades of an emerald-cut diamond according to an embodiment of the present invention for a diamond with L/W ratio 1.35, corner ratio 14%, a table % of 55, crown breaks of 4-3 and pavilion breaks of 3-3-3 (4-tier) over ranges of crown main angles of 33.0-45.0 and pavilion main angles of 43.0-48.0.

(21) FIG. 14 is a map of the light performance grades of an emerald-cut diamond according to an embodiment of the present invention for a diamond with L/W ratio 1.35, corner ratio 14%, a table % of 55, crown breaks of 4-6 and pavilion breaks of 3.3-3 (4-tier) over ranges of crown main angles of 35.0-45.0 and pavilion main angles of 43.0-48.0.

(22) FIG. 15 is a map of the light performance grades of an emerald-cut diamond according to an embodiment of the present invention for a diamond with L/W ratio 1.35, corner ratio 14%, a table so of 55, crown breaks of 4-3 and pavilion breaks of 4-2-2 (4-tier) over ranges of crown main angles of 35.0-45.0 and pavilion main angles of 43.0-48.0.

DETAILED DESCRIPTION

(23) In the following description and claims, the diamond components, angles, lengths, widths, thicknesses, grades, etc., are determined in accordance with the American Gem Society Laboratories (“AGS”) definitions and standards in effect on the filing date of this application. Percentages and ratios are based on the width of the diamond measured at the girdle (“girdle width”), unless otherwise indicated.

(24) As used herein and in the claims, light performance grades and components thereof are determined in accordance with the AGS grading standards in effect on the filing date of this application. The AGS grades are determined by evaluating deductions from perfect or Ideal (AGS) and rounded to the nearest whole number, e.g., a stone with deductions of 0.49 would be assigned an AGS 0-grade, while a stone with deductions of 1.51 would be assigned an AGS grade of 2. Thus, the lower the grade, the better the light performance. Unless otherwise indicated, as used herein “grade” refers to the AGS light performance grade.

(25) “Grade map” as used herein is any tool that provides light performance deductions or grades as a function of one or more cutting parameters. The maps may be in the form of charts or tables as in the AGS Cutting Chart Guidelines mentioned above, or may be a mathematical model.

(26) The “0-grade domain density” of a grade map, as used herein, represents the fraction of pavilion main/crown main angle combinations that obtain a grade of 0 out of the total pavilion main/crown main angle combinations in a grade map or portion thereof. For example, FIG. 6 shows 30 pavilion/crown main angle combinations having a light performance grade of 0, and a total of 594 total pavilion/crown main angle combinations, for a 0-grade domain density of 0.051 (or 5.1%). Similarly, FIG. 4 shows a 0-grade domain density of 0.156, and FIG. 7 shows a 0-grade domain density of 0.077.

(27) As used herein, all numbers and values have a range of accuracy that is plus or minus one-half of the significant digit provided, unless otherwise indicated. For example, an angle given as 41.00 degrees is ±0.005 degrees; or a range of angles given as “28 to 45 degrees (±0.25)” is 27.75 to 45.25. The parenthetical indication of plus or minus following a list of values or ranges of values is intended to apply to each non-zero value and each of the non-zero range endpoint values, whereas the non-zero values may be up to or equal to the indicated plus value.

(28) In an embodiment, an emerald-cut diamond comprises a ratio of length to width, measured at a girdle between a crown and a pavilion (“the girdle width”), of from about 1.35 to 1.40 (±0.025); a table having a width of from about 55 to 60 percent (±0.5) of the width of the diamond measured at the girdle; a corner ratio of from about 13.5 to 14.5 percent, preferably about 14.0 percent (±0.25) of the girdle width; a girdle thickness of up to about 3 percent, preferably from greater than 0 up to about 3 percent (±0.5) of the girdle width; a crown main facet tier adjacent the girdle having an angle with respect to the table plane of from about 28 to 45 degrees (±0.25); a first crown break angle between the crown main tier and an adjacent crown second tier from about 2 to 6 degrees, preferably about 3 to 5 degrees (±0.5); a second crown break angle between the crown second tier and an adjacent crown third tier from about 2 to 6 degrees, preferably about 3 to 6 degrees (±0.5); a pavilion main facet tier adjacent the girdle having an angle with respect to the table plane of from about 43 to 48 degrees (±0.25); a first pavilion break angle between the pavilion main tier and an adjacent pavilion second tier from about 2 to 6 degrees, preferably about 3 to 5 degrees (±0.5); and/or a second pavilion break angle between the pavilion second tier and an adjacent pavilion third tier from about 2 to 6 degrees, preferably about 2 to 5 degrees (±0.5).

(29) In a preferred embodiment, the first crown break angle is from about 3 to 5 degrees (±0.5); the second crown break angle is from about 3 to 6 degrees (±0.5); the first pavilion break angle is from about 3 to 5 degrees (±0.5); and the second pavilion break angle is from about 2 to 5 degrees (±0.5).

(30) The emerald-cut diamond may have a light performance grade of 1, preferably a light performance grade of 0. For example, the emerald-cut diamond may preferably have light performance deductions less than about 1.50, or less than about 1.00, or more preferably AGS light performance deductions less than about 0.50, or less than about 0.40, or less than about 0.30, or less than about 0.20, or less than about 0.10, or about 0.00 (±0.005).

(31) The pavilion third tier of the emerald-cut diamond may terminate at a culet, e.g., the diamond may be a “three-tier” emerald-cut. In a preferred embodiment, the emerald-cut diamond may have first and second crown break angles of about 4 and 3 degrees (±0.5), respectively. The crown main angle is preferably from about 35 to 45 degrees (±0.25). Preferably, the first and second pavilion break angles are from about 3 to 5 degrees (±0.5), and more preferably as follows: the first pavilion break angle is about 3 degrees, the second pavilion break angle is about 4 or 5 degrees (±0.5), the pavilion main angle is from about 43.0 to 46.5 degrees (±0.25), and especially where an AGS light performance grade is 0; or, the first and second pavilion break angles are about 5 and 4 degrees (±0.5), respectively, the pavilion main angle is from about 43.5 to 48.0 degrees (±0.25), and especially where the AGS light performance grade is 0; or, the first and second pavilion break angles are each about 5 degrees (±0.5), the pavilion main angle is from about 44.5 to 48.0 degrees (±0.25), and especially where the AGS light performance grade is 0.

(32) In an embodiment, the emerald-cut diamond may further comprise a third pavilion break angle between the pavilion third tier and an adjacent pavilion fourth tier from about 2 to 6 degrees, preferably about 2 to 5 degrees (±0.5), e.g., the diamond may be a “four-tier” emerald-cut where the fourth tier terminates at a culet, or it may have 5 or more tiers. Preferably, the four-tier emerald-cut may have a first pavilion break angle from about 2 to 4 degrees, preferably about 3 to 4 degrees (±0.5), a second pavilion break angle from about 2 to 4 degrees, preferably about 2 to 3 degrees (±0.5), and a third pavilion break angle from about 2 to 4 degrees, preferably about 2 to 3 degrees (±0-5). The four-tier emerald-cut diamond may have a light performance grade of 1, preferably 0.

(33) In another aspect, the present invention provides a method for cutting an emerald-cut diamond with Excellent or preferably Ideal light performance characteristics. The method may allow selection of crown and pavilion mains angles from a relatively wide range that may facilitate achieving a light performance grade of 1 or preferably 0, for example. By selecting from within these parameters in a 0-grade domain of a grade map, the cutter has improved flexibility for the selection, and greater forgiveness in deviations from the selected parameters during cutting, to obtain an emerald-cut diamond with a light performance grade of 1 or preferably 0, for example.

(34) In one embodiment, a method for cutting a diamond to have emerald-cut parameters comprises cutting the diamond in a rectangular plan with a ratio of length to width, measured at a girdle between a crown and a pavilion of the diamond, of from about 1.35 to 1.40 (±0.025); forming corners on the diamond having a ratio of from about 14.0 to 14.5 percent (±0.25) of the girdle width; forming a table on the crown of the diamond having a width of from about 5; to 60 percent (±0.5) of the girdle width; forming a thickness of the girdle from greater than 0 up to about 3 percent (±0.5) of the girdle width; forming a crown main facet tier adjacent the girdle having an angle with respect to the table plane of from about 28 to 45 degrees (±0.25); forming a crown second tier facet adjacent the crown main facet tier having a first crown break angle between the crown main and second tiers from about 2 to 6 degrees, preferably about 3 to 5 degrees (±0.5); forming a crown third tier facet adjacent the second crown tier facet having a second crown break angle between the crown second and third tiers from about 2 to 6 degrees, preferably about 3 to 6 degrees (±0.5); forming a pavilion main facet tier adjacent the girdle having an angle with respect to the table plane of from about 43 to 48 degrees (±0.25); forming a pavilion second tier facet adjacent the pavilion main facet tier having a first pavilion break angle between the pavilion main and second tiers from about 2 to 6 degrees, preferably about 3 to S degrees (±0.5); and forming a pavilion third tier facet adjacent the pavilion second tier facet having a second pavilion break angle between the pavilion second and third tiers from about 2 to 6 degrees, preferably about 2 to 5 degrees (±0.5). In an embodiment, the method may comprise polishing the diamond to at least an Excellent polish and at least Excellent symmetry (AGS), preferably Ideal polish and Ideal symmetry (AGS).

(35) In any embodiment, the method may further comprise selecting cutting parameters comprising crown and pavilion main tier facet angles from a 1- or preferably 0-grade domain of a grade map, and cutting the diamond according to the selected cutting parameters, preferably to obtain a light performance grade of 1 or more preferably 0. In any embodiment, the method may comprise selecting the ratio of length to width, the corner ratio, the table percentage, first and second crown break angles, first and second pavilion break angles, and ranges of the crown main angle and pavilion main angle corresponding to a grade map of light performance deductions for combinations of the crown and pavilion main angles over said ranges; selecting cutting parameters comprising crown and pavilion main angles from the grade map corresponding to a 0-grade domain; and cutting the diamond sufficiently close to the selected cutting parameters, preferably within 0.25 degrees of each of the selected crown and pavilion main tier and first and second break angles, to obtain a light performance grade of 0. For example, the emerald-cut diamond may preferably have light performance deductions less than about 1.50, or less than about 1.00, or more preferably light performance deductions less than about 0.50, or less than about 0.40, or less than about 0.30, or less than about 0.20, or less than about 0.10, or about 0.00 (±0.005). In any embodiment, the grade map may comprise a 0-grade domain density equal to or greater than 0.25, preferably greater than or equal to 0.30, 0.35, 0.40, 0.50, or 0.60.

(36) The pavilion third tier of the emerald-cut diamond may be terminated at a culet, e.g., the diamond may be a “three-tier” emerald-cut. In a preferred embodiment, the emerald-cut diamond may be formed with first and second crown break angles of about 4 and 3 degrees (±0.5), respectively. The crown main angle is preferably formed at from about 35 to 45 degrees (±0.25). Preferably, the first and second pavilion break angles are formed at from about 3 to 5 degrees (±0.5), and more preferably as follows. the first pavilion break angle is formed at about 3 degrees, the second pavilion break angle is formed at about 4 or 5 degrees (±0.5), the pavilion main angle is formed at from about 43.0 to 46.5 degrees (±0.25), and especially where an AGS light performance grade is 0; or, the first and second pavilion break angles are formed at about 5 and 4 degrees (±0.3), respectively, the pavilion main angle is formed at from about 43.5 to 48.0 degrees (±0.25), and especially where the AGS light performance grade is 0; or, the first and second pavilion break angles are each formed at about 5 degrees (±0.5), the pavilion main angle is formed at from about 44.5 to 48.0 degrees (±0.25), and especially where the AGS light performance grade is 0.

(37) In any embodiment of the method for cutting the three-tier emerald-cut diamond, the method may further comprise selecting the ratio of length to width, the corner ratio, the table percentage, first and second crown break angles, first and second pavilion break angles, and ranges of the crown main angle and pavilion main angle corresponding to a grade map of light performance deductions for combinations of the crown and pavilion main angles over said ranges; selecting cutting parameters comprising crown and pavilion main angles from the grade map corresponding to a 0-grade domain; and cutting the diamond sufficiently close to the selected cutting parameters, preferably within 0.25 degrees of each of the selected crown and pavilion main and first and second break angles, to obtain a light performance grade of 0.

(38) In an embodiment, the method may further comprise forming a third pavilion break angle between the pavilion third tier and an adjacent pavilion fourth tier from about 2 to 6 degrees, preferably about 2 to 5 degrees (±0.5), e.g., the diamond may be a “four-tier” emerald-cut where the fourth tier terminates at a culet, or it may have 5 or more tiers. Preferably, the four-tier emerald-cut may be formed with a first pavilion break angle from about 2 to 4 degrees, preferably about 3 to 4 degrees (±0.5), a second pavilion break angle from about 2 to 4 degrees, preferably about 2 to 3 degrees (±0.5), and a third pavilion break angle from about 2 to 4 degrees, preferably about 2 to 3 degrees (±0.5). In any embodiment, the method may further comprise selecting the ratio of length to width, the corner ratio, the table percentage, first and second crown break angles, first, second, and third pavilion break angles, and ranges of the crown main angle and pavilion main angle corresponding to a grade map of light performance deductions for combinations of the crown and pavilion main angles over said ranges; selecting cutting parameters comprising crown and pavilion main angles from the grade map corresponding to a 0-grade domain; and cutting the diamond sufficiently close to the selected cutting parameters, preferably within 0.25 degrees of each of the selected crown and pavilion main and first and second break angles and the third pavilion break angle, to obtain a light performance grade of 0.

(39) In any embodiment, the method may further comprise selecting cutting parameters comprising crown and pavilion main tier facet angles from an AGS an AGS 0 area of an ASET map; and cutting the diamond according to the selected cutting parameters to obtain an AGS light performance grade of 1, or preferably 0. Preferably, the ASET map comprises a continuous AGS 0 area having extents of at least 1.5 degrees, preferably at least 2.0 degrees, more preferably at least 2.5 degrees over domains of the crown and pavilion mains angles.

(40) The invention is illustrated by the following examples.

Examples

(41) In the following examples, ASET images for virtual diamonds were simulated, and the light performance deductions, grades and maps, calculated by the American Gem Society Laboratories.

(42) Example 1: Light performance deductions and ASET images were determined for a virtual emerald-cut diamond having a table % of 55, L/W ratio 1.35, corner ratio 14%, crown breaks of 4-3 and pavilion breaks of 3-4 over ranges of crown main angles of 35.0-45.0 degrees and pavilion main angles of 43.0-48.0 degrees. The light performance deductions are shown in the map of HG. SA and the corresponding ASET images in FIG. 8B. The 0-grade domain density is 0.411.

(43) Example 2: Light performance deductions and ASET images were determined for a virtual emerald-cut diamond having a table % of 55, L/W ratio 1.35, corner ratio 14%, crown breaks of 4.3 and pavilion breaks of 3-5 over ranges of crown main angles of 35.0-45.0 degrees and pavilion main angles of 43.0-48.0 degrees. The light performance deductions are shown in the map of FIG. 9A and the corresponding ASET images in FIG. 9B. The 0-grade domain density is 0.472.

(44) Example 3: Light performance deductions and ASET images were determined for a virtual emerald-cut diamond having a table % of 55, L/W ratio 1.35, corner ratio 14%, crown breaks of 4-3 and pavilion breaks of 4.5 over ranges of crown main angles of 35.0-45.0 degrees and pavilion main angles of 43.0-48.0 degrees. The light performance deductions are shown in the map of FIG. 10A and the corresponding ASET images in FIG. 10B. The 0-grade domain density is 0.450.

(45) Example 4: Light performance deductions and ASET images were determined for a virtual emerald-cut diamond having a table % of 55, L/W ratio 1.35, corner ratio 14%, crown breaks of 4-3 and pavilion breaks of 5-4 over ranges of crown main angles of 35.0-45.0 degrees and pavilion main angles of 43.0-48.0 degrees. The light performance deductions are shown in the map of FIG. 11A and the corresponding ASET images in FIG. 11B. The 0-grade domain density is 0.441. FIG. 3A is a side sectional view of an Example 4 diamond with a crown main angle of 35.0 degrees and a pavilion main angle of 48.0 degrees, which has 0.00 performance deductions (FIG. 11A) and the ASET image 200 (FIG. 11B).

(46) Example 5: Light performance deductions and ASET images were determined for a virtual emerald-cut diamond having a table % of 55, L/W ratio 1.35, corner ratio 14%, crown breaks of 4-3 and pavilion breaks of 5-5 over ranges of crown main angles of 35.0-45.0 degrees and pavilion main angles of 43.0-48.0 degrees. The light performance deductions are shown in the map of FIG. 12A and the corresponding ASET images in FIG. 12B. The 0-grade domain density is 0.372.

(47) Example 6: Light performance deductions were determined for virtual emerald-cut diamonds having a table % of 55, L/W ratio 1.35, corner ratio 14%, crown breaks of 4-3 and pavilion breaks of 3-3-3 (4-tier) over ranges of crown main angles of 35.045.0 degrees and pavilion main angles of 43.0-48.0 degrees. The light performance deductions are shown in the map of FIG. 13. The 0-grade domain density is 0.693. FIG. 3B is a side sectional view of an Example 6 diamond with a crown main angle of 40.0 degrees and a pavilion main angle of 45.0 degrees, which has 0.00 performance deductions (FIG. 13).

(48) Example 7: Light performance deductions were determined for virtual emerald-cut diamonds having a table % of 55, L/W ratio 1.35, corner ratio 14%, crown breaks of 4-6 and pavilion breaks of 3-3-3 (4-tier) over ranges of crown main angles of 35.045.0 degrees and pavilion main angles of 43.0-48.0 degrees. The light performance deductions are shown in the map of FIG. 14. The 0-grade domain density is 0.571.

(49) Example 8: Light performance deductions were determined for virtual emerald-cut diamonds having a table % of 55, L/W ratio 1.35, corner ratio 14%, crown breaks of 4-3 and pavilion breaks of 4-2-2 (4-tier) over ranges of crown main angles of 35.0-45.0 degrees and pavilion main angles of 43.0-48.0 degrees. The light performance deductions are shown in the map of FIG. 15. The 0-grade domain density is 0.420.

(50) As seen in Table 2 below, the 0-grade domain areas are unexpectedly more extensive than in the published guidelines, with higher densities of the 0-grade domains.

(51) TABLE-US-00002 TABLE 2 0-Grade Domain Density Comparison 0-Grade Pavilion Corner Table Crown Pavilion Domain FIG. Tiers L/W Ratio % Breaks Breaks Density  4 3 1.40 0.14 55 5.5-2.5 11.5-4.5  0.156 (Prior art)  6 3 1.40 0.14 55 7-7 11-7  0.051 (Prior art)  7 3 1.40 0.14 60 7-7 11-7  0.077 (Prior art)  8A 3 1.35 0.14 55 4-3 3-4 0.411  9A 3 1.35 0.14 55 4-3 3-5 0.472 10A 3 1.35 0.14 55 4-3 4-5 0.450 11A 3 1.35 0.14 55 4-3 5-4 0.441 12A 3 1.35 0.14 55 4-3 5-5 0.372 13 4 1.35 0.14 55 4-3 3-3-3 0.693 14 4 1.35 0.14 55 4-6 3-3-3 0.571 15 4 1.35 0.14 55 4-3 4-2-2 0.420

(52) Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. It is the express intention of the applicant not to invoke 35 U.S.C. § 112(f) for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function and without any recitation of structure.