A
diamond´s shape and “cut” is the result of a professional
cutter removing a diamond from the original stone. When a
perfect diamond is cut out, it´s angles and proportions are
not sacrificed for size. How a diamond is cut determines the
brilliance and fire of the diamond—or how it reflects light.
A poorly cut diamond reflects light poorly, while a diamond
cut correctly reflects light more perfectly, giving it the
brilliance most desired. Many gemologists consider cut the
most important diamond characteristic because even if a diamond
has perfect color and clarity, a diamond with a poor cut will
have less brilliance. The following diagrams demonstrate how
light is reflected in various cuts of a diamond and the importance
cut plays in selecting a beautiful and, thus, more valuable
diamond.
As illustrated above, a diamond´s proportions are critical
in its value and luster. When shopping for a diamond, you
will either see a diamond´s cut graded from Poor Cut
to Ideal Cut, given an AGS rating of 0 (best) to 10,
or more commonly, broken down into the following proportions:
depth % and table %. You may also see the following listed
in a report: girdle thickness, culet size, crown
angle, pavilion angle, and pavilion %, which are based
upon how the individual parts of the diamond relate
to each other. Symmetry and polish, in addition
to proportion also play a role in a diamond´s beauty.
There is a difference between diamond shape and cut. However,
when searching for a diamond, you will sometimes see “cut”
refer to the shape of the diamond. On the diamond´s GIA Report,
the shape is referred to as “diamond shape and cutting style”.
Every diamond shape does not have the same proportions. Each
requires its own guidelines in order to achieve maximum brilliance.
To simplify your search, below is a table that describes desirable
table and depth percentages for the most popular diamond shapes.
Ideal cut: This is a very rare cut. It reflects nearly
all light that enters the diamond and creates the maximum
fire and brilliance.
Premium cut: Reflects almost as much light as
the Ideal Cut, but for a lower price.
Very Good cut: These diamonds reflect most of
the light that enters them. With these diamonds, the cutters
have chosen to stray slightly from the preferred diamond proportions
in order to create a larger diamond.
Good cut: These diamonds reflect a good bit of
the light that enters them. The cutter has chosen to create
the largest possible diamond from the original rough stone,
rather than cutting extra weight off to create a smaller higher
quality diamond.
Fair cut: A Fair Cut diamond will not be as brilliant
as a good cut diamond.
Poor cut: These diamonds are deep and narrow or
shallow and wide and tend to lose most of the light out the
sides and bottom.
The American Gem Society (AGS) Diamond Grading Laboratory
uses a cut grade system that assigns diamonds a cut grade
as a number between 0 and 10. The AGS Cut Grade reflects 3
key elements: proportions, symmetry, and polish.
Proportions are the sizes and angles of the diamond´s main
parts. Symmetry is the balance and evenness of its faceting
and shape. Polish refers to the diamond´s surface quality,
including the presence or absence of characteristics such
as abrasions, scratches, nicks and polish wheel lines. The
AGS Ideal 0 cut grade represents the very best in diamond
cutting.
Crown: The top portion of a diamond extending from
the girdle to the table.
Culet: The point on the bottom of a diamond's
pavilion. The culet is often polished as a flat facet so that
it does not get chipped. These days the cutter usually closes
this facet to a point, but sometimes it remains as a small
extra facet. In some cases, you will find that a round brilliant
cut has 57 facets, and sometimes 58; the 58th facet is the
culet. If the culet is too big, the diamond acts as a window
from the table through the culet. The result is that you can
see right out the “hole” the culet appears to make in the
center bottom of the diamond. Your diamond’s culet should
be pointed (no culet), very small, small or medium because
these are not visible to the naked eye. Large to extremely
large culets may be visible to the naked eye and can look
like an inclusion.
Girdle: The dividing line between the crown, or
top part of the stone and the pavilion, or bottom part of
the stone. Girdle thickness can be very thin in part of a
stone and very thick in another part. That is why it is expressed
as a range. The girdle can also be faceted, or not. A faceted
girdle usually improves the look of the stone, and involves
having the cutter polish facets into the girdle.
Pavilion: The pavilion is the bottom part of the
diamond, below the girdle. The height of the pavilion greatly
contributes to the diamond's overall brilliance. A pavilion
that is too long or too shallow in proportion to the rest
of the diamond will result in a duller looking diamond.
Table: The diamond´s largest facet, the top flat
part of the diamond you look at when the stone is face-up.
Depth percent: the depth of the diamond (from table
to culet) relative to the width of the stone (girdle diameter).
Diamonds that have ideal to very fine cut with proper total
depth percentage provide the greatest brilliance.
Table Percent: the table size relative to the
diamond's average width.
Pavilion Angle and Pavilion Depth Percent: Neither
is included in GIA Reports. The Pavilion depth percent is
calculated by dividing crown height by the diamonds average
girdle diameter. AGS diamonds rated 0 (Ideal) have a pavilion
angle of 40.5 degrees - 41 degrees and a pavilion depth percent
of 42.2% - 43.8%. AGS rated 2 have a pavilion angle of 39.7
degrees - 41.7 degrees and a pavilion depth percent of 41.7%
- 44.8%.
Polish: The finishing or final polishing of the
facets, or flat surfaces. Poorly polished facets may reduce
the intensity of light reflected from, or refracted into and
out of, a diamond. Polish is graded as Excellent, Very Good,
Good, Fair or Poor on a GIA report. If the polish is rated
as fair or poor, visual performance may be noticeably reduced.
Symmetry: the alignment of the diamond´s facets.
With poor symmetry, light can be misdirected as it enters
and exits the diamond. Symmetry is graded the same way as
polish on a GIA report: Excellent, Very Good, Good, Fair or
Poor.
| Table
%: |
 |
53-61% |
|
| Crown
angle: |
|
33-36 degrees |
|
| Girdle
thickness: |
|
Thin - Slightly
thick |
|
| Depth
%: |
|
59-64% |
|
| Culet
size: |
|
None - Very
small |
|
| Symmetry: |
|
Good - Excellent |
|
| Polish: |
|
Good - Excellent |
|
