123:(the lower half below the girdle), which has only the apex cut off to form the culet, around which 8 extra facets are sometimes added. Over time it has become usual for most girdles to be faceted. Many girdles have 32, 64, 80, or 96 facets; these facets are not counted in the total. While the facet count is standard, the actual proportions (crown height and angle, pavilion depth, etc.) are not standardised. Some gem cutters refer to an American brilliant cut or a Scandinavian brilliant cut. According to Green et al. 2001:
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loose under a gemscope to see the pattern very well. Although the hearts and arrows property is indicative of a top-tier cut, it does not always mean the diamond will be the most brilliant. Optimal facet placement is the key to brilliance and more important than facet patterning. Not all ideal round cuts will have the hearts and arrows effect either.
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the diamond. A diamond's panorama is three-dimensional. Although diamonds are highly symmetrical, light can enter a diamond from many directions and many angles. This factor further highlights the need to reevaluate
Tolkowsky's results, and to recalculate the effects of a diamond's proportions on its
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A diamond that has the top facet or "table facet" exactly perpendicular to the bottom of the diamond or "pavilion" and has its other facets precisely aligned with excellent symmetry, may show patterns that look like arrows from the top and hearts from the bottom. Generally it will need to be viewed
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Another important point to consider is that
Tolkowsky did not follow the path of a ray that was reflected more than twice in the diamond. However, we (Green et al.) now know that a diamond's appearance is composed of many light paths that reflect considerably more than two times within that diamond.
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Polish and symmetry are two important aspects of cut. The polish grade describes the smoothness of the diamond's facets and the symmetry grade refers to alignment of the facets. With poor polish, the surface of a facet can be dull and may create blurred or dull sparkle. The stone may look like it
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So-called "painted" girdles have thinner girdles where the main facets touch the girdle than where adjacent upper girdle facets touch the it. These stones (such as EightStar-brand diamonds) have less light leakage at the edge of the stone (for a given crown angle, pavilion angle, and table ratio).
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So-called "cheated" girdles have thicker girdles where the main facets touch the girdle than where adjacent upper girdle facets touch the girdle. These stones weigh more for a given diameter, average girdle thickness, crown angle, pavilion angle, and table ratio, and have worse optical performance,
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The GIA began grading cut on every grading report beginning in 2006, based on their comprehensive study of 20,000 proportions with 70,000 observations of 2,000 diamonds. The single descriptive words are as follows: Excellent, Very Good, Good, Fair, and
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The distance from the viewer's eye to the diamond is important. The 2005 AGS cut standards are based on a distance of 25 centimeters (about 10 inches). The 2004 HCA cut standards are based on a distance of 40 centimeters (about 16 inches).
131:. Just as a two-dimensional slice of a diamond provides incomplete information about the three-dimensional nature of light behavior inside a diamond, this two-dimensional slice also provides incomplete information about light behavior
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Several groups have developed diamond cut grading standards. These standards differ somewhat on which proportions make the best cut. There are certain proportions that are considered best by two or more groups, however.
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The
American Gem Society (AGS) standards changed in 2005 in order better to match Tolkowsky's model and Octonus' ray tracing results. The 2005 AGS standards penalize stones with "cheated" girdles. They grade from 0 to
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The relationship between the crown angle and the pavilion angle has the greatest effect on the look of the diamond. A slightly steep pavilion angle can sometimes be complemented by a shallower crown angle and
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The HCA (Holloway Cut
Adviser) changed several times between 2001 and 2004. As of 2004, an HCA score below two represented an excellent cut. The HCA distinguishes between brilliant, Tolkowsky, and fiery
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Once again, we can see that
Tolkowsky's predictions are helpful in explaining optimal diamond performance, but they are incomplete by today's technological standards.
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Figure 1 assumes that the "thick part of the girdle" is the same thickness at all 16 "thick parts". It does not consider the effects of indexed upper girdle facets.
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107:(if any—not part of Tolkowsky's original design) are cut from the ideal brilliant. The modern round brilliant consists of 58 facets (or 57 if the
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always results in a dramatic loss of weight; rarely is this loss less than 50%. The round brilliant cut is preferred when the crystal is an
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Some diamonds with painted girdles receive lower grades in the GIA's cut grading system, for reasons given in a 2005 GIA article.
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The AGA standards may be the strictest. David Atlas, who developed the AGA standards, has suggested that they are overly strict.
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Blodgett, Troy; Gilbertson, Al; Geurts, Ron; Green, Barak; Johnson, Mary; Reinitz, Ilene; Yantzer, Phil (June 3, 2005).
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needs to be cleaned. Because of the lack of symmetry, light can be misdirected as it enters and exits the diamond.
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in 1919. The ideal proportions are 100% diameter, 53% table, 43.1% pavilion and 16.2% crown. The girdle and
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Green, Barak; Gilbertson, Al; Reinitz, Ilene; Johnson, Mary; Shigley, James (August 17, 2001).
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427:"OctoNus Software, Moscow State University, Bruce Harding, and others have posted work there"
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Most round brilliant diamonds have roughly the same girdle thickness at all 16 "thick parts".
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402:"HCA: defining ideal cut diamonds (a detailed explanation of the "Holloway Cut Advisor")"
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is excluded), ordinarily today cut in two pyramids placed base to base: 33 on the
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of the stone), truncated comparatively near its base by the table, and 25 on the
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Diamond Design: A Study of the
Reflection and Refraction of Light in a Diamond.
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Diamond Design - A Study of the
Reflection and Refraction of Light in a Diamond
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Diamond Design - A Study of the
Reflection and Refraction of Light in a Diamond
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Because every facet has the potential to change a light ray's plane of travel,
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Video: How a
Diamond is Cut and Polished at Eurostar Diamonds International
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353:. London: E. & F. N. Spon, Ltd., New York: Spon & Chamberlain.
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332:. London: E. & F. N. Spon, Ltd., New York: Spon & Chamberlain.
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every facet must be considered in any complete calculation of light paths
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i.e., their upper girdle facets appear dark in some lighting conditions.
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Figures 1 and 2 show the facets of a round brilliant diamond.
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Diamond proportions and facets, for the round brilliant cut.
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Other proportions also affect the look of the diamond:
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Figure 2 is adapted from Figure 37 of Marcel
Tolkowsky's
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Gemstone cut with many facets to increase the brilliance
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so as to have exceptional brilliance. The underside is
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The length of the lower girdle facets affects whether
347:Tolkowsky, Marcel (1919) . Paulsen, Jasper (ed.).
99:The original round brilliant-cut was developed by
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459:Antique Jewelry University - Brilliant Cut
476:edited by Jasper Paulsen, Seattle, 2001.)
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169:Solitary ring and diamond before mounting
311:from the original on September 30, 2012.
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299:"What did Marcel Tolkowsky really say?"
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185:The table ratio is highly significant.
38:shows off the many reflecting facets.
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472:London: E. & F.N. Spon, Ltd. (
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357:from the original on 2023-03-12.
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34:A scattering of "brilliant" cut
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77:are more likely to be cut in a
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326:. In Paulsen, Jasper (ed.).
239:Hearts and arrows phenomenon
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380:GIA Rapaport Diamond Report
322:Tolkowsky, Marcel (1919) .
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87:Facet proportions and names
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468:Tolkowsky, Marcel (1919).
373:"Painting and Digging Out"
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400:Garry Holloway (2001).
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136:appearance aspects.
389:on August 29, 2006.
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245:Hearts and arrows
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16:(Redirected from
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495:Gemstone cutting
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18:Round brilliant
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270:Princess cut
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474:Web edition
324:"Figure 37"
260:Diamond cut
161:Cut grading
484:Categories
437:2013-01-28
412:2005-03-19
281:References
176:vice versa
71:octahedron
80:fancy cut
50:or other
44:brilliant
431:Archived
406:Archived
355:Archived
334:Archived
306:Archived
254:See also
121:pavilion
52:gemstone
36:diamonds
133:outside
67:crystal
63:conical
48:diamond
117:girdle
75:macles
59:facets
387:(PDF)
376:(PDF)
309:(PDF)
302:(PDF)
226:Poor.
218:cuts.
113:crown
109:culet
105:culet
46:is a
139:...
222:10.
55:cut
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363:^
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42:A
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