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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,
including Ideal Cut. For more information on the Ideal Cut, please see our
detailed discussion, The Ideal Cut: A Consumer's Guide in the Learning
Center.
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. For more information on the most commonly-occurring
types of blemishes, please see our detailed discussion, The Four Cs:
Clarity.
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. For more information on brilliance,
please see our detailed discussion, The Four Cs: Cut.
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 designed to maximize brilliance. Round diamonds, ovals,
radiants, princesses, hearts, marquises, and pears all fall within this
category of cut. Other styles of faceting arrangements include the step
cut (in which facets are arranged in concentric rows around the table and
the culet) 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). Note: Some jewelers use the term "Brilliant cut" as a
synonym for "round diamond." For more information on the most common
shapes of diamonds, please see our discussion and image gallery on Fancy
Shapes.
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. We will not sell any
diamond in which the clouds are severe enough to affect the brilliance of
the diamond. For more information on clouds and other types of inclusions,
please see our discussion, The Four Cs: Clarity.
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). For more information, please see our detailed discussion,
The Four Cs: Color.
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. For more information on how crown angles
affect a diamond's beauty, please see our detailed discussion, The Four
Cs: Cut. |
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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. For more information, please
see our detailed discussion, The Four Cs: Cut.
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. For more information, please see
our detailed discussion, The Four Cs: Cut.
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. For more information
on the most common shapes of diamonds, please see our discussion and image
gallery on Fancy Shapes.
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. For more information on the most common shapes of diamonds, please
see our discussion and image gallery on Fancy Shapes.
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. For more information on feathers and other types
of inclusions, see our discussion, The Four Cs: Clarity.
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. For more
information on finish and how it is graded, please see our discussion, The
Four Cs: Cut.
Fire: Please see our definition of Dispersion, above.
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. For additional
information on the nature of fluorescence and its effect on diamonds,
please see our detailed discussion, Judging the Impact of Fluorescence.
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. |
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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. For more information on the
most common shapes of diamonds, please see our discussion and image
gallery on Fancy Shapes.
Inclusion: A clarity characteristic found within a diamond. Most
inclusions were created when the gem first formed in the earth. For more
information on the most commonly-occurring types of inclusions, please see
our detailed discussion, The Four Cs: Clarity.
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. We do not advise purchasing any laser-drilled diamonds graded
SI1 or higher. Though this is a permanent and acceptable clarity
treatment, We will not sell a diamond with a drill hole unless the
customer understands what the treatment is, and what he is buying. For
more information, please see our detailed discussion, The Four Cs:
Clarity.
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.
In the ratio, width is always represented by the value "1." To determine
the value of the length, divide the millimeter measurement of the length
by the millimeter measurement of the width. These millimeter measurements
can be found at the top left-hand side of the diamond grading report. The
measurements are always listed in the following order: Length x Width x
Depth.
Here is an example of how the length-to-width ratio would be used:
Consider a princess cut weighing 1.05 carats that has millimeter
measurements of 5.73 x 5.52 x 4.11.
The first value represents the diamond's length and the second value
represents its width. To calculate the length-to-width ratio, divide
5.73 by 5.52.
The result is 1.04 and it represents the length as it compares to the
diamond's width (which you will remember is always represented by the
value "1"). This means the length-to-width ratio for this diamond is
1.04 to 1, which is an almost perfectly square diamond. This diamond
will appear square to your eye.
Marquise Cut: A type of fancy shape diamond which is elongated
with points at each end. For more information on the most common shapes of
diamonds, please see our discussion and image gallery on Fancy Shapes.
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). For more
information, please see our detailed discussion, The Four Cs: Clarity.
Oval Cut: A type of fancy shape diamond which is essentially an
elongated version of a round cut. For more information on the most common
shapes of diamonds, please see our discussion and image gallery on Fancy
Shapes.
Pavé: A style of jewelry setting in which numerous small diamonds
are mounted close together to create a glistening diamond crust that
covers the whole piece of jewelry and obscures the metal under it.
Pavilion: The lower portion of the diamond, below the girdle.
Pear Cut: A type of fancy shape diamond that resembles a teardrop.
For more information on the most common shapes of diamonds, please see our
discussion and image gallery on Fancy Shapes.
Point: A unit of measurement used to describe the weight of
diamonds. One point is equivalent to one-hundredth of a carat. For more
information, please see our discussion, The Four Cs: Carat Weight.
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. For more
information, please see our discussion, The Four Cs: Cut.
Princess Cut: A type of brilliant cut fancy shape that can be
either square or rectangular. For more information on the most common
shapes of diamonds, please see our discussion and image gallery on Fancy
Shapes.
Radiant Cut: A type of brilliant cut fancy shape that resembles a
square or rectangle with the corners cut off. For more information on the
most common shapes of diamonds, please see our discussion and image
gallery on Fancy Shapes.
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.
In the ratio, width is always represented by the value "1." To determine
the value of the length, divide the millimeter measurement of the length
by the millimeter measurement of the width. These millimeter measurements
can be found at the top left-hand side of the diamond grading report. The
measurements are always listed in the following order: Length x Width x
Depth.
Here is an example of how the length-to-width ratio would be used:
Consider a princess cut weighing 1.05 carats that has millimeter
measurements of 5.73 x 5.52 x 4.11.
The first value represents the diamond's length and the second value
represents its width. To calculate the length-to-width ratio, divide
5.73 by 5.52.
The result is 1.04 and it represents the length as it compares to the
diamond's width (which you will remember is always represented by the
value "1"). This means the length-to-width ratio for this diamond is
1.04 to 1, which is an almost perfectly square diamond. This diamond
will appear square to your eye.
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. For more
information on the most common shapes of diamonds, please see our
discussion and image gallery on Fancy Shapes.
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). For more information on the
most common shapes of diamonds, please see our discussion and image
gallery on Fancy Shapes.
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. For more information, please see our discussion, The Four
Cs: Cut.
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. For more information, please see our
discussion, The Four Cs: Cut.
Trilliant Cut: A type of brilliant fancy shape that is triangular.
For more information on the most common shapes of diamonds, please see our
discussion and image gallery on Fancy Shapes.
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