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It's easiest to explain diamond
anatomy by referencing a round brilliant-cut diamond,
pictured below. All elements here relate to the
cut
of a diamond.
When buying a diamond, one should consider more
overall aspects of the cut, as cut (one of the
"4
Cs") has it's own
rating scale which already mostly accounts
for all the items below. Thus, you can feel comfortable
gauging your purchase based upon its general cut
reference.
However, occasionally some diamonds are available
with details on these these more technical terms
(below) mentioned in relation to the cut of the
diamond.
Two notable items are the "girdle" and
"culet". As you can see below, both
are at places on the diamond where they would
come to a sharp point or knife-like edge. While
their effect on the overall reflection of light
(a most important part of a diamond) may be diminished
by other factors like pavilion and crown angle,
girdle and culet are most simply mentioned to
note a final aspect of nearness-to-perfection
of the diamond.
In certain ring mounting types, girdle and culet
are effectively buried within the ring. Even when
set in popular mounting styles like pronged solitaires,
these aspects of the diamond are almost invisible
to the untrained eye. Thus, seeking an expenditure
on a stone of better girdle and culet is an expense
some choose not to make.
Athensia offers pre-set diamonds which already
meet high-quality cut standards in terms of girdle
and culet, if such aspects are not mentioned in
the diamond you are considering. But for your
reference, it's considered less favorable if a
diamond has "thicker" girdle or "larger"
culet, as they are then not as precise.
It's advised again that you familiarize yourself
with the basics
of cut to better understand the items below.
(Source: GIA Diamond Cut Grading System)
Diameter
The distance measured between two opposing points
along the girdle's outline. The minimum and maximum
girdle diameters are determined by taking the
average from a number of diameter measurements.
Diameter is reported to the nearest hundredth
of a millimeter (0.01 mm).
Total Depth
Total depth (measured from table plane to culet)
relative to the average diameter reported to the
nearest tenth of a percentage point (0.1%).
Table
Average table size is relative to the average
diameter, reported to the nearest whole percentage
point (1%). Table size is measured from bezel
point to bezel point (where the table stops and
drops at an angle towards the girdle); the average
of four measurements is used. The table, when
viewed from above, is not a circle - but rather
a circular shape with multiple angled sides that
come together at bezel points.
Crown/Crown Angle
Average of all eight crown angles, reported to
the nearest half of a degree (0.5°). A crown
angle is the angle of the bezel facet plane relative
to the table plane.
Crown Height %
Average crown height relative to the average diameter,
reported to the nearest half of a percentage point
(0.5%). Crown height is measured from the table
plane to the intersection of the bezel facet with
the girdle.
Pavilion Angle
Average of all eight pavilion angles, reported
to the nearest multiple of 0.2° (e.g., 41.0°,
41.4°). A pavilion angle is the angle of the
main facet plane relative to the table plane.
Pavilion Depth %
Average pavilion depth relative to the average
diameter, reported to the nearest half of a percentage
point (0.5%). Pavilion depth is measured from
the culet to the intersection of the pavilion
main facet with the girdle.
Girdle Thickness
Described and reported by the GIA Laboratory as
an average range from the thinnest to the thickest
areas (i.e., where the upper and lower halves
meet). Descriptions include extremely thin, very
thin, thin, medium, slightly thick, thick, very
thick, and extremely thick. "Extremely thin"
appears as a knife-edge; that is, the crown meets
the pavilion with no girdle in between. "Extremely
thick" would have no sharp edge, and even
a vertical flat area between the paviliion and
crown as the eye follows the image above.
Culet Size
Described and reported by the GIA Laboratory as
the average width of the culet relative to the
average diameter of the girdle. Descriptions include
none, very small, small, medium, slightly large,
large, very large, and extremely large. "None"
is used when there is no culet facet, which is
sometimes referred to by the trade as a pointed
culet. As this part of the diamond is basically
the point of a cone, the sharper the point, the
smaller the culet size.
NEXT:
6. "Ring Metal & Settings"...
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