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9/3/2010
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| In modern round brilliant cut diamonds larger than melee sizes, this is
not very common, as most round brilliants are cut from a roughly pyramid
shaped piece of rough (half the octahedral crystal) which is usually
slightly steeper angled than needed for correct pavilion angles. Thus
its far more common to see pavilion angles that are too deep, than too
shallow. Those distorted crystals which might tend to produce fisheye
proportions are more often cut into fancy shapes, so as to avoid that
problem. But you DO see the fisheye look in some of the old european cut
stones, and in occasional melee diamonds. |
| The big gotchas with regard to princess cut proportions is that the
usually desired numbers go right out the window... Normally, one wants a
43 percent pavilion in a round brilliant cut, in order to achieve maximum
internal reflection, and thus, maximum brilliance. The measurement is
usually made as depth of the pavilion divided by the width (narrowest
dimension). In practice, its usually determined with an optical
comparator, either a GIA proportionscope, or a similar eyepiece reticle
used in a microscope. In either case, the number is related by convention
to the width of the stone. In princess cuts, however, that narrow
dimension, the width, is not the optically important or active direction.
Most of the pavilion facets radiate from the corners of the stone, and the
sides are simply squared up, with facets that have little effect on
overall brilliance. So one usually finds depth percentages that seem to
be far too deep. In fact, if you measure those pavilions using a corner. |
| As the pavilion angles get too deep (above about 43 to 44 percent), the
table reflection gets darker, and larger. As this effect increases, the
diamond starts to look more like a donut, with a brilliant periphery, and
a mostly non-brilliant dark area filling up the table region. If this is
so extreme as to really just look like a black table area (sometimes
extending to the star facets as well), then its nicknamed a nailhead.
While this degree of deep pavilion, like the fisheye degree of shallow
pavilion, is not very common (The stones are quite ugly and hard to sell,
so few cutters push the limits that far), an intermediate range of deep
pavilion is quite common. More so, in fact, than truly well cut stones. |
|
%T Diamond Cut Audio Restoration Tools 32
%T Enhance CD/R
%A Diamond Cut Productions, Inc.
%I PO Box 305, Hibernia NJ 07842
%C www.diamondcut.com or www.tracertek.com (888-8TRACER)
%D v3.0 1998 |
| Black Diamond Diamonds in the Rough 92 Lundmark Jamie
Black Diamond Diamonds in the Rough 93 Beech Kris
Black Diamond Diamonds in the Rough 94 Zigomanis Michael
Black Diamond Diamonds in the Rough 95 Mezei Branislav
Black Diamond Diamonds in the Rough 96 Keefe Sheldon
Black Diamond Diamonds in the Rough 99 Shvidki Denis
Black Diamond Diamonds in the Rough 100 Jackman Barret
Black Diamond Diamonds in the Rough 101 Ouellet Maxime
Black Diamond Diamonds in the Rough 102 Kraft Milan
Black Diamond Diamonds in the Rough 103 Ralph Brad
Black Diamond Diamonds in the Rough 104 Volkov Alexei
Black Diamond Diamonds in the Rough 106 Bell Mark
Black Diamond Diamonds in the Rough 107 Jardine Ryan
Black Diamond Diamonds in the Rough 108 Kudroc Kristian
Black Diamond Diamonds in the Rough 109 Milley Norm
Black Diamond Diamonds in the Rough 110 Heerema Jeff
Black Diamond Diamonds in the Rough 111 Kristek Jaroslav
Black Diamond Diamonds in the Rough 112 Sellars Luke
Black Diamond Diam. |
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