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| Home � Daimond Advice � Diamond Dictionary |
| Diamond Dictionary |
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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.
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 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."
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. gddiamond.com 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.
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. For more information on
how crown angles affect a diamond's beauty. |
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.
For more information.
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. For more information on finish and
how it is graded.
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.
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. gddiamond.com does not advise purchasing
any laser-drilled diamonds graded SI1 or higher. Though this is a permanent and
acceptable clarity treatment, gddiamond.com will not sell a diamond with a drill hole
unless the customer understands what the treatment is, and what he is
buying.
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
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.
Pav�: 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.
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. For more information on the most common shapes of
diamonds.
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.
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 pav�
jewelry and other jewelry that utilizes numerous small diamonds set closely
together. For more information on the most common shapes of
diamonds.
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.
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.
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