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Diamonds: Parts of the Stone
Subheadline
HERE ARE THREE
BASIC PARTS TO EVERY CUT DIAMOND:
- The crown (top)
- The girdle (around the middle)
- The pavilion (the bottom).
CROWN
The crown consists of a large flat area on top called
the table, and a number of facets. As the diamond catches the light,
the job of the crown is to split the light entering the diamond
into white light, which gives the stone its brilliance, and colored
light, which gives it fire, or dispersion.
GIRDLE
The girdle is the thin, unpolished band around the widest
part of the diamond. The function of the girdle is to protect the
edge of the stone from chipping (even though diamond is the hardest
natural substance on earth, it can be chipped!)
PAVILION
The pavilion has the most important job, which is to
reflect the light that passes through the crown back into your eyes.
Think of it as a cone lined with mirrors. The light enters the diamond
through the crown, splits into white and colored light, bounces
off the facets of the pavilion back up through the crown, where
you see it as sparkle! But to achieve the maximum sparkle —
that magic combination of brilliance and fire — the diamond
must be well cut and cut in the proper proportions.
THE SIZE OF THE
TABLE, THE SYMMETRY OF THE FACETS, THE THICKNESS OF THE GIRDLE,
AND THE ANGLE OF THE PAVILION MUST ALL WORK TOGETHER TO GIVE THE
DIAMOND THE SPARKLE YOU WANT.
TABLE
The size of the table, as a percentage of the crown,
is important because it determines the amount of brilliance, or
white light, the diamond will reflect. For example, if the table
is 60% of the diameter of the crown, 60% of the light you see will
be brilliance and 40% will be fire, or dispersion. Avoid a diamond
with a table area of 65% or higher. It will give the diamond too
much brilliance, and not enough fire--and the diamond will look
fuzzy or foggy. (The only exception to this rule is emerald and
rectangular cut diamonds that can have a 65% table. This includes
all princess cuts, quadrillions and radiants.) HERE'S THE FORMULA:
Table area
53-60% = GREAT! Table area 61-64% = GOOD! Table area 65%+ =
except emerald and rectangular cuts.
FACETS
The typical diamond is cut with 58 facets, 33 on the
crown and 25 on the pavilion. On a well-proportioned stone, these
facets will be uniform and symmetrical. If they are not, the diamond's
ability to refract and reflect light will suffer. Furthermore, a
poorly-cut diamond just won't look right to the eye. The sad fact
is, 75% of all rounds and 88% of all other shapes on the market
are poorly proportioned! Poorly proportioned stones are more profitable
for the dealer, because they retain more of the weight of the rough
or uncut diamond.
GIRDLE
You don't want a diamond with a girdle that's too thin,
or one that's too thick — you want one that's just right! The
whole purpose of the girdle is to protect the edge of the stone
from chipping. A girdle that's too thin doesn't give enough protection.
A girdle that's too thick does protect against chipping, but it
doesn't look so good. So you want a diamond with a medium girdle,
neither too thin nor too thick. How do you tell? Look at the diamond
from the side. If it looks like there's a white chalk line around
the middle of the stone, the girdle is too thick. If you don't see
any girdle at all with the naked eye, look at the same area of the
stone with a 10X loupe. If you can't see a girdle with the loupe,
it's too thin.
PAVILION
The job of the pavilion is most important of all: to reflect
light. The light enters the diamond through the table and the facets
of the crown, passes through the diamond, and is reflected back
by the facets of the pavilion. Here's the important part: The angle
of the pavilion for a round diamond must be between 40-41.5 degrees.
40.75 degrees is perfect. For marquise, pear, and ovals, the perfect
angle perfect angle is 40 degrees, but an acceptable range is 39.25--40.75
degrees. For emerald and rectangular cuts, perfect is 45.05 and
an acceptable range is 43.3-46.8 degrees. If the pavilion angle
is not exactly right it will not reflect the light properly, and
the diamond won't have the sparkle it should. In a round diamond,
there's a dramatic loss of sparkle if the angle is even a tenth
of a degree above 41.5 or below 40 degrees. In marquise, pear,
or oval, maximum sparkle is achieved with a 40 degree pavilion
angle, but the angle can be increased or decreased by as much as
three-fourths of a degree with only a 10% loss of sparkle. Emerald
and rectangular cut diamonds have the widest allowable variance
of 1.75 degrees. Each extreme will also cause a 10 percent loss
of sparkle.
CROWN
ANGLE The angle of the crown is also important, but it
doesn't have to be quite as precise as the pavilion angle. The angle
of the crown should be 32-35 degrees. If it's smaller than 32 degrees,
the diamond is what we call spread-cut. This makes the table area
too large and the girdle too thin, and we already know what problems
that causes. If the angle of the crown is above 35 degrees, it makes
the diamond "top heavy." This results in a smaller diameter,
making the diamond look smaller than it really is. The last thing
you want is a one-carat diamond that looks like a 3/4 carat!
CULET
Finally, at the very bottom of the diamond--the base
of the pavilion--there may be a small facet called the culet. If
this facet is too large, when you look straight down through the
table it will look like the diamond has a hole in the middle. Make
sure the stone has no culet or a very small culet.
TWO
OTHER IMPORTANT DIAMOND MEASUREMENTS Two other measurements
to consider are: total depth and length-to-width ratio.
TOTAL
DEPTH is a simple, straightforward measurement: take
the height of the stone and divide it by the diameter of the stone.
For a fancy stone, the diameter is measured at its widest part.
The answer should be in the 56%-61% range. If it's not, it means
there's something wrong with the crown angle and/or the pavilion
angle, or the girdle thickness. (The only exception to this
rule is emerald or rectangular cut diamonds that can have a total
depth of 65%.)
THE
LENGTH-TO-WIDTH RATIO is used to determine if a fancy-shaped
diamond (anything other than round) is well-proportioned. For example,
we don't want to buy a marquise that is so skinny it looks like
a banana, or one that's so fat it looks like a football. Pleasing
proportions aside, the length-to-width ratio also affects a phenomenon
known as the bow-tie. Let me explain.
Fancy shapes are
not symmetrical — only a round is. And because fancy
stones aren't symmetrical, they all have a bow-tie — two triangular
shadows in the middle of the diamond where light leaks out the bottom.
If the length-to-width ratio is off, it will intensify the bow-tie
in the stone! For a marquise diamond, the length should be no less
than 1.75 times the width, and no more than 2 times the width. For
pear shapes, the length should be no less than 1.5 times the width,
and no more than 1.75 times the width. For emerald and oval shapes,
the length should be no less than approximately 1.3 times the width,
and no more than 1.75 times the width.
PROPORTIONS
MADE EASY GIA has made it easier to determine if a diamond
is well-proportioned by dividing all cut diamonds into four classes.
Essentially, Class One and Class Two diamonds are well-proportioned;
Class Three and Class Four diamonds are not. Class One diamonds
are investment-quality stones, beautifully proportioned and priced
to match. If your objective is to buy a beautiful diamond to wear,
Class Two is fine.
FRED'S
ADVICE: Don't go below Class Two. And if the jeweler
doesn't know what the GIA classes are, move on!
PROPORTION
AND PRICE A poorly proportioned diamond is worth as much
as 40% less than a well proportioned stone. One reason for the difference
in worth is that it takes a 3-carat rough, which is a diamond as
it's found in nature, to produce a well proportioned 1-carat cut
stone. But it only takes a 2-carat rough to produce a poorly proportioned
1-carat stone. A poorly proportioned diamond will not sparkle nearly
as much as a well proportioned diamond. If a diamond is poorly proportioned,
only 35-40% of the light that enters it will reflect back up into
your True Love's eyes, while a well proportioned diamond will reflect
close to 90% of the light. A woman wants a diamond to be "big,
clean, white and sparkly," and it won't sparkle unless it's
well proportioned.
by Fred Cuellar,
author of the best-selling book "How to Buy a Diamond." More questions?
Ask the Diamond Guy®
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