Dictionary of Diamond Terms
American
Gem Society (AGS):
An educational institution for gemological studies. The AGS Labs were
created primarily to develop and promote universally-accepted standards
for grading cut.
Blemish:
A clarity characteristic that occurs on the surface of a diamond.
Though some blemishes are inherent to the original rough diamond, most
are the result of the environment the diamond has encountered since
it was unearthed.
Brilliance:
The brightness that seems to come from the very heart of a diamond.
It is the effect that makes diamonds unique among all other gemstones.
While other gemstones also display brilliance, none have the power to
equal the extent of diamond's light-reflecting power. Brilliance is
created primarily when light enters through the table, reaches the pavilion
facets, and is then reflected back out through the table, where the
light is most visible to your eye.
Brilliant
Cut:
One of three styles of faceting arrangements. In this type of arrangement,
all facets appear to radiate out from the center of the diamond toward
its outer edges. It is called a brilliant cut because it is designed
to maximize brilliance. Round diamonds, ovals, radiants, princesses,
hearts, marquises, and pears all fall within this category of cut.
Carat :
The unit of weight by which a diamond is measured. One carat equals
200 milligrams, or 0.2 grams. The word comes from the carob bean, whose
consistent weight was used in times past to measure gemstones.
Carbon
Spots:
An inaccurate term used by some people in the jewelry industry to describe
the appearance of certain inclusions in a diamond. The term refers to
included crystals that have a dark appearance, rather than a white or
transparent appearance, when viewed under a microscope. In most cases,
these dark inclusions are not visible to the naked eye, and do not affect
the brilliance of the diamond.
Cleavage:
The propensity of crystalline minerals, such as diamond, to split in
one or more directions either along or parallel to certain planes, when
struck by a blow. Cleavage is one of the two methods used by diamond
cutters to split rough diamond crystals in preparation for the cutting
process (sawing is the other method).
Clouds:
A grouping of a number of extremely tiny inclusions that are too small
to be distinguishable from one another, even under magnification. The
result is that, under a microscope, this grouping often looks like a
soft transparent cloud inside the diamond. Of course, clouds cannot
be seen with the naked eye. Usually, this sort of inclusion does not
significantly impact a diamond's clarity grade.
Color
Grading:
A system of grading diamond colors based on their colorlessness (for
white diamonds) or their spectral hue, depth of color and purity of
color (for fancy color diamonds). For white diamonds, GIA and AGS use
a grading system which runs from D (totally colorless) to Z (light yellow).
Crown:
The upper portion of a cut gemstone, which lies above the girdle. The
crown consists of a table facet surrounded by either star and bezel
facets (on round diamonds and most fancy cuts) or concentric rows of
facets reaching from the table to the girdle (on emerald cuts and other
step cuts).
Crown
angle:
The angle at which a diamond's bezel facets (or, on emerald
cuts, the row of concentric facets) intersect the girdle plane. This
gentle slope of the facets that surround the table is what helps to
create the dispersion, or fire, in a diamond. White light entering at
the different angles in broken up into its spectral hues, creating a
beautiful play of color inside the diamond. The crown angle also helps
to enhance the brilliance of a diamond.
Culet:
A tiny flat facet that diamond cutters sometimes add at the bottom of
a diamond's pavilion. Its purpose is to protect the tip of the pavilion
from being chipped or damaged. Once a diamond is set in jewelry, though,
the setting itself generally provides the pavilion with sufficient protection
from impact or wear. Large or extremely large culets were common in
diamonds cut in the early part of this century, such as the Old European
or Old Mine Cut. However, such large culets are rarely seen today. Most
modern shapes have either no culet at all, or a small or very small
culet.
Cut:
This refers both to the proportions and finish of a polished diamond.
As one of "the Four Cs" of diamond value, it is the only man-made
contribution to a diamond's beauty and value.
Depth:
The height of a diamond from the culet to the table. The depth is measured
in millimeters.
Depth
Percentage:
On a diamond grading report, you will see two different measurements
of the diamond's depth-the actual depth in millimeters (under "measurements"
at the top of the report) and the depth percentage, which expresses
how deep the diamond is in comparison to how wide it is. This depth
percentage of a diamond is important to its brilliance and value, but
it only tells part of the story. Where that depth lies is equally important
to the diamond's beauty; specifically, the pavilion should be just deep
enough to allow light to bounce around inside the diamond and be reflecting
out to the eye at the proper angle. Keep in mind, also, that a depth
percentage that might be excessive for one diamond cut might be necessary
for another type of cut. For example, a 75% or 78% depth in a princess
cut diamond would be typical and quite attractive. However, a depth
of even 65% would be unnecessary and even detrimental to a round diamond's
beauty.
Diamond:
A crystal made up of 99.95% pure carbon atoms arranged in an isometric,
or cubic, crystal arrangement. It is this unique arrangement of the
carbon atoms that makes diamond look and behave differently from other
pure carbon minerals such as graphite (the soft black material used
to make pencils).
Diamond
Cutting:
The method by which a rough diamond that has been mined from the earth
is shaped into a finished, faceted stone. As a first step, cleaving
or sawing is often used to separate the rough into smaller, more workable
pieces that will each eventually become an individual polished gem.
Next, bruting grinds away the edges, providing the outline shape (for
example, heart, oval or round) for the gem. Faceting is done in two
steps: during blocking, the table, culet, bezel and pavilion main facets
are cut; afterward, the star, upper girdle and lower girdle facets are
added. Once the fully faceted diamond has been inspected and improved,
it is boiled in hydrochloric and sulfuric acids to remove dust and oil.
The diamond is then considered a finished, polished gem.
Diamond
Gauge:
An instrument that is used to measure a diamond's length, width and
depth in millimeters.
Dispersion:
Arranged around the table facet on the crown are several smaller facets
(bezel and star facets) angled downward at varying degrees. These facets,
and the angles at which they are cut, have been skillfully designed
to break up white light as it hits the surface, separating it into its
component spectral colors (for example, red, blue and green). This effect,
which appears as a play of small flashes of color across the surface
of the diamond as it is tilted, is what we refer to as the diamond's
dispersion (also called "fire"). This play of color should
not be confused with a diamond's natural body color (normally white,
though sometimes yellow, brown, pink or blue in the case of fancy color
diamonds) which is uniform throughout the entire diamond and is constant,
regardless of whether it is being tilted or not.
Emerald
Cut:
A square or rectangular-shaped diamond with cut corners. On the crown,
there are three concentric rows of facets arranged around the table
and, on the pavilion, there are three concentric rows arranged around
the culet. This type of cut is also known as a Step Cut because its
broad, flat planes resemble stair steps.
Eye-Clean:
An term used in the jewelry industry to describe a diamond with no blemishes
or inclusions that are visible to the naked eye (i.e. a human eye which
is not aided by magnifying devices such as a jeweler's loupe or a microscope).
Facet:
The smooth, flat faces on the surface of a diamond. They allow
light to both enter a diamond and reflect off its surface at different
angles, creating the wonderful play of color and light for which diamonds
are famous. The table below shows all the facets on a round brilliant
cut diamond. A round brilliant has 58 facets (or 57 if there is no culet).
The shape, quantity, and arrangement of these facets will differ slightly
among other fancy shapes.
Fancy
Shape:
Any diamond shape other than round.
Feathers:
These are small fractures in a diamond. They are usually caused by the
tremendous stress that the diamond suffered while it was growing underground.
In some cases the feather both begins and ends within the diamond's
surface and, in other cases, the feather begins inside the diamond and
extends to the surface. When viewed under magnification, some feathers
are transparent and others have a light white appearance to them. The
term "feather" comes from the fact that, under magnification,
these fractures often seem to have an indistinct, feathery shape to
them. While the idea of buying a diamond with "fractures"
may sound scary, the reality is that, with normal wear and care, most
feathers pose no risk to the diamond's stability. Consider this: even
with the feathers, these diamonds survived their growth and their journey
to the surface intact. Once on the surface, they also survived the mining
process, as well as the brutal stresses of the diamond cutting process.
Though diamonds are certainly not invulnerable to damage, basic consideration
to their care and handling during everyday wear will most likely protect
them over the course of several human lifetimes.
Finish:
This term refers to the qualities imparted to a diamond by the skill
of the diamond cutter. The term "finish" covers every aspect
of a diamond's appearance that is not a result of the diamond's inherent
nature when it comes out of the ground. The execution of the diamond's
design, the precision of its cutting details, and the quality of its
polish are all a consideration when a gemologist is grading finish.
If you examine a diamond's grading report, you will see its finish graded
according to two separate categories: polish and symmetry.
Fire:
See "dispersion".
Fluorescence:
An effect that is seen in some gem-quality diamonds when they are exposed
to long-wave ultraviolet light (such as the lighting frequently seen
in dance clubs). Under most lighting conditions, this fluorescence is
not detectable to the eye. However, if a diamond is naturally fluorescent,
it will emit a soft colored glow when held under an ultraviolet lamp
or "black light." Fluorescence is not dangerous to the diamond
or to the wearer; it is a unique and fascinating quality that occurs
naturally in a number of gems and minerals.
Gemological
Institute of America (GIA):
Founded in 1931 by Roger Shipley, this non- profit organization upholds
the highest standards for grading diamonds and other precious gems.
The GIA has one of the most-respected and well-regarded gemological
laboratories in the world; GIA was responsible for developing and standardizing
the diamond grading system that is used today by nearly all other gem
labs.
Girdle:
The outer edge, or outline, of the diamond's shape. The girdle is not
graded, but rather it is described by its appearance at its thinnest
and thickest points. The descriptions of girdle thickness range as follows:
extremely thin; thin; medium; slightly thick; thick; extremely thick.
While it is less desirable for a round diamond to display an extremely
thin or extremely thick girdle, such girdle widths are more common and
acceptable in fancy shapes.
For
example, shapes such as pears, marquises or hearts may be cut with
extremely thick girdles at their points (and at the cleft, in the
case of a heart) in order to protect these delicates corners from
damage. Most diamonds have smooth girdles that are fashioned by a
"bruter" (a diamond cutter who is responsible for shaping
the diamond's basic outline) early on in the cutting process. In some
cases, cutters go a step further and do additional cutting on the
girdle. In these cases, they may decide to create a "polished"
girdle or a "faceted" girdle. In both cases, the difference
between these and a regular, smooth girdle is generally not distinguishable
to the eye. A polished or faceted girdle doesn't improve a diamond's
grade. Most labs grade a girdle's thickness, not its appearance.
Heart-shape
Cut:
A type of fancy diamond cut, which is cut to resemble the popular Valentine's
Day shape.
Inclusion:
A clarity characteristic found within a diamond. Most inclusions were
created when the gem first formed in the earth.
Laser-Drill
Holes:
One of the few man-made inclusions that can occur inside a diamond.
Why on earth would anyone want to drill holes into a perfectly good
diamond? It may seem counter-intuitive, but drilling this type of hole
into a diamond can actually raise its clarity grade. In some diamonds,
the clarity grade may be determined mainly by the presence of just one
or two dark included crystals in a diamond that is otherwise relatively
free of inclusions. In certain circumstances, the diamond cutter will
decide to use a procedure to remove the dark inclusions and, hopefully,
increase the clarity of the diamond. First, a hole is precisely made
with state-of-the-art equipment; it extends no further than it needs
to, and its width is so small (about the size of a pinpoint) that a
loupe or microscope is usually required to detect it. Next, a strong
acid solution is forced into the new hole.
Since
diamonds are resistant to acids, the solution actually dissolves the
included crystal while leaving the diamond completely unharmed. The
end result is a more transparent diamond. The structural stability
of the diamond is not compromised in any way by this hole, and the
process is permanent.
Length-to-width
ratio:
A comparison of how much longer a diamond is than it is wide. It is
used to analyze the outline of fancy shapes only; it is never applied
to round diamonds. There's really no such thing as an 'ideal' ratio;
it's simply a matter of personal aesthetic preferences. For example,
while many people are told that a 2 to 1 ratio is best for a marquise,
most people actually tend to prefer a ratio of around 1.80 to 1 when
they actually look at marquises. And though the standard accepted range
for the length-to- width ratio of a marquise generally falls between
1.70 to 1 and 2.05 to 1, there are customers who insist on having 'fatter'
marquises of about 1.60 to 1 and other customers who want longer, thinner
marquises of 2.25 to 1.
Marquise
Cut:
A type of fancy shape diamond which is elongated with points
at each end.
Naturals:
Small parts of the original rough diamond's surface which are left on
the polished diamond, frequently on or near the girdle. While these
are blemishes, they might also be regarded as a sign of skilled cutting;
the presence of a natural reflects the cutter's ability to design a
beautiful polished gem, while still retaining as much of the original
crystal's weight as possible. In many cases, naturals do not affect
the clarity grade. In most cases, they are undetectable to the naked
eye.
Another
type of natural is the Indented Natural; in this case, the portion
of the original rough diamond's surface which is left on the polished
diamond dips slightly inward, creating an indentation. Usually, the
cutter makes an effort to cut the polished diamond so that the indented
natural will be confined to either the girdle or the pavilion (making
it undetectable to the naked eye in the face-up position).
Oval
Cut:
A type of fancy shape diamond which is essentially an elongated
version of a round cut.
Pavilion:
The lower portion of the diamond, below the girdle.
Pear
Cut:
A type of fancy shape diamond that resembles a teardrop.
Point:
A unit of measurement used to describe the weight of diamonds. One point
is equivalent to one-hundredth of a carat.
Polish:
Refers to any blemishes on the surface of the diamond which are not
significant enough to affect the clarity grade of the diamond. Examples
of blemishes that might be considered as 'polish' characteristics are
faint polishing lines and small surface nicks or scratches. Polish is
regarded as an indicator of the quality of as diamond's cut; it is graded
as either Ideal, Excellent, Very Good, Good, Fair or Poor.
Princess
Cut:
A type of brilliant cut fancy shape that can be either square or rectangular.
Radiant
Cut:
A type of brilliant cut fancy shape that resembles a square or rectangle
with the corners cut off.
Ratio:
A comparison of how much longer a diamond is than it is wide. It is
used to analyze the outline of fancy shapes only; it is never applied
to round diamonds. There's really no such thing as an 'ideal' ratio;
it's simply a matter of personal aesthetic preferences. For example,
while many people are told that a 2 to 1 ratio is best for a marquise,
most people actually tend to prefer a ratio of around 1.80 to 1 when
they actually look at marquises. And though the standard accepted range
for the length-to-width ratio of a marquise generally falls between
1.70 to 1 and 2.05 to 1, there are customers who insist on having 'fatter'
marquises of about 1.60 to 1 and other customers who want longer, thinner
marquises of 2.25 to 1.
Semi-mount:
A jewelry setting that has the side stones already mounted, but which
contains an empty set of prongs which are intended to mount a diamond
center stone that the customer selects separately.
Single-cut:
A very small round diamond with only 16 or 17 facets, instead of the
normal 57 or 58 facets of a full cut round brilliant. Single cuts are
occasionally used for pavé jewelry and other jewelry that utilizes
numerous small diamonds set closely together.
Step
Cut:
One of three styles of faceting arrangements. In this type of arrangement
(named because its broad, flat planes resemble stair steps), there are
three concentric rows of facets arranged around the table and, on the
pavilion, there are three concentric rows arranged around the culet.
Other styles of faceting arrangements include the brilliant cut (in
which all facets radiate out from the center of the diamond toward its
outer edges) and the mixed cut (in which either the crown or pavilion
of a diamond is cut as a brilliant cut, and the other part of the diamond
is cut as a step cut).
Symmetry: Refers to variations in a diamond's symmetry. The small variations can
include misalignment of facets or facets that fail to point correctly
to the girdle (this misalignment is completely undetectable to the naked
eye). Symmetry is regarded as an indicator of the quality of as diamond's
cut; it is graded as either Ideal, Excellent, Very Good, Good, Fair
or Poor.
Table:
The flat facet on the top of the diamond. It is the largest facet on
a cut diamond.
Table
percentage:
The value which represents how the diameter of the table facet compares
to the diameter of the entire diamond. So, a diamond with a 60% table
has a table which is 60% as wide as the diamond's outline. For a round
diamond, gemologists calculate table percentage by dividing the diameter
of the table, which is measured in millimeters (this millimeter measurement
does not appear on diamond grading reports) by the average girdle diameter
(an average of the first two millimeter measurements on the top left-hand
side of a diamond grading report). For a fancy shape diamond, table
percentage is calculated by dividing the width of the table, at the
widest part of the diamond, by the millimeter width of the entire stone
(this total width measurement is the second of the three millimeter
values in the top left-hand corner of the diamond grading report. Contrary
to popular misconception, having a small table percentage (53% to 57%)
does not make a round diamond any more brilliant than a diamond with
a larger table.
Trilliant
Cut:
A type of brilliant fancy shape that is triangular.