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Diamond Proportions Explained
An ideal cut diamond is cut to ideal proportions. Let's take a
look at some problems you may encounter with diamond proportioning. We will
first look at the finer points before going on to the major cutting issues. The
images below will help explain what you are looking at with these photographs.
If necessary, return to Part 1 and review the diamond parts and names.
The girdle provides enough depth to protect the diamond during wear, while
not being so thick as to detract from the stone’s beauty. Below are some
examples of the good, the bad and the ugly.
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Thin to Medium Girdle
A well-made girdle, thick enough to protect diamond during setting and wear.
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Very thin to slightly thick girdle
A dangerous combination for possible breakage.
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Slightly thick faceted
Girdle is slightly thick overall and facted. |
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Thick to very thick
A common, frosted girdle. This one is an indented natural. It is part of the
original diamond crystal surface, left on the stone when it was cut in an
attempt to maintain the best possible symmetry or roundness of the finished
diamond. |
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Extremely thick girdle
Sometimes the naturals are so big that they are simply polished off as an
extra facet on the diamond, most often on the girdle as you see below. This is a
huge extra facet and will make the stone look flat from the top. Normally, small
extra facets are not rare and do not greatly detract from the beauty of a
diamond. This one is an exceptionally large extra facet, which will degrade the
beauty and value of the diamond. |
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Pointing error in symmetry of facets
All facet junctions should meet in perfect points in a properly cut diamond.
Below, the pavilion facet of the diamond does not meet at a point at the girdle
as it should. This is called a pointing error and is minor as long as there are
only a few and the pointing errors are small. |
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Very large culet
Culets are the very bottom of the stone where it comes to a point. The culet
below is very large. It appears to be a hole in the bottom of the diamond and
will allow light to leak out. This will count against the diamond’s
proportioning, since a culet this big can be visible to the unaided
eye. |
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Out of round, symmetry error
Noticeably out of round, this is a poor quality stone. The bulges on the
corners are so apparent that is almost looks squared off. Because of its out of
roundness this diamond would be priced very cheaply, regardless of clarity and
color.
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