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Brilliant
(diamond cut) 7195
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Brilliant
is one of the most used cuts for diamonds.
Even with modern techniques, the cutting and polishing
of a diamond crystal always results in a dramatic loss
of weight; rarely is it less than 50%. The round brilliant
cut is preferred when the crystal is an octahedron, as
often two stones may be cut from one such crystal. Oddly
shaped crystals such as macles are more likely to be cut
in a fancy cut—that is, a cut other than the round
brilliant—which the particular crystal shape lends
itself to.
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History
Item #
p6808
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The brilliant
cut was introduced in the middle of the 17th century.
The first brilliants were known as Mazarins. They had
seventeen facets on the crown (upper half) and are called
double-cut brilliants.
Vincent Peruzzi, a Venetian polisher, increased the number
of crown facets from 17 to 33 (triple-cut brilliants),
thereby dramatically increasing the fire and brilliance
of the cut gem — already much better in the double-cut
brilliant than in the rose cut. When seen today, diamonds
of that cut seem quite dull compared to modern-cut ones.
Around 1900, the development of diamond saws and good
jewellery lathes enabled the development of modern diamond
cuts, chief among them the round brilliant cut. In 1919,
Marcel Tolkowsky analyzed this cut. His calculations took
both brilliance (the amount of white light reflected)
and fire (flashes of spectral colors) into consideration,
creating a delicate balance between the two. His geometric
calculations can be found in his book on Diamond Design.
In the 1970s, Bruce Harding developed another mathematical
model for gem design. Since then, several groups have
used computer models (e.g., MSU, OctoNus, GIA, and folds.net)
and specialized scopes to optimize the round brilliant
cut.
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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 be complemented by a shallower
crown angle, and vice versa.
Other proportions also affect the look of the diamond:
• The table ratio is highly significant.
• The length of the lower girdle facets affects
whether Hearts and arrows can be seen in the stone, under
certain viewers.
• Indexing the upper girdle facets
o Most round brilliant diamonds have roughly the same
girdle thickness at all 16 "thick parts".
o 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 (their upper
girdle facets appear dark in some lighting conditions).
o So-called "painted" girdles have thinner
girdles where the main facets touch the girdle than
where adjacent upper girdle facets touch the girdle.
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).
Several groups have developed diamond cut grading standards.
• The AGA standards may be the strictest. David
Atlas (who developed the AGA standards) has suggested
that they are overly strict.
• The HCA 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 cuts.
• The AGS standards changed in the summer of 2005
to better match Tolkowsky's model and Octonus' ray tracing
results. The 2005 AGS standards penalize stones with
"cheated" girdles.
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).
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Anniversary symbols
7154
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The modern
round brilliant consists of 58 facets (or 57 if the culet
is excluded); 33 on the crown (the top half above the
middle or girdle of the stone) and 25 on the pavilion
(the lower half below the girdle). In recent decades,
most girdles are 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
universally agreed upon. One may speak of the American
cut or the Scandinavian standard (Scan. D.N.), to give
but two examples.
Figures 1 and 2 show the facets of a round brilliant diamond.
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.
Figure 2 is adapted from Figure 37 of Marcel Tolkowsky's
Diamond Design, which was originally published in 1919.
Since 1919, the lower girdle facets have become longer.
As a result, the pavilion main facets have become narrower.
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Item # 6978
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There may
exist variations in national traditions.
Furthermore, there exist rather confusingly only partially
overlapping, partially contradictory lists of anniversary
gifts (such as wedding
stones), separate from the 'traditional' names.
The concepts of a person's birthday stone, birth stone
and zodiac stone, by contrast, are fixed for life according
to the day of the week, month or astrological sign corresponding
to the recipient's birthday.
View our beautiful Cubic Zirconia CZ Platinum Jewelry
Anniversary
Rings Collection |
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