Bezel: A facet on the
Crown, or upper part of the Diamond above the Girdle.
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
Carat Weight: The metric
carat, which equals 0.200 gram, is the standard unit of weight
for diamonds and most other gems. If other factors are equal,
the more a stone weighs, the more valuable it will be.
Cavity: An inclusion
consisting of a large or deep opening in the stone.
Clarity: A stone's relative
position on a flawless to imperfect scale. Clarity
characteristics are classified as inclusions (internal) or
blemishes (external). The size, number, position, nature, and
color or relief of characteristics determines the clarity grade.
Very few diamonds are flawless, that is, show no inclusions or
blemishes when examined by a skilled grader under 10X
magnification. If other factors are equal, flawless stones are
Cloud: A group of tiny
white inclusions which result in a milky or cloudy appearance.
Coated Diamond: A diamond
colored by a surface coating which masks the true body-color;
the coating may be extensive (entire pavilion, for example), but
is more often limited to one or two pavilion facets or a spot on
Color: Grading color in the
normal range involves deciding how closely a stone's body color
approaches colorlessness. Most diamonds have at least a trace of
yellow or brown body color. With the exception of some natural
fancy colors, such as blue, pink, purple, or red, the colorless
grade is the most valuable.
Crown: The upper part of
the diamond above the girdle. Crown consists of a large flat
area on top called a table, and several facets below it. Culet:
The smallest facet at the bottom of the diamond.
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 is 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: The proportions and
finish of a polished diamond (also called make). Cut can also
mean shape, as in emerald cut or marquise cut. Proportions are
the size and angle relationships between the facets and
different parts of the stone. Finish includes polish and details
of facet shape and placement. Cut affects both the weight yield
from rough and the optical efficiency of the polished stone; the
more successful the cutter is in balancing these considerations,
the more valuable the stone will be.
Depth: The height of a
diamond from the culet to the table. The depth is measured in
Depth Percentage: 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. 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 Gauge: An
instrument that is used to measure a diamond's length, width and
depth in milli-meters.
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).
Faceted Girdle: Sometimes
cutters polish the girdle into 32 facets.
Abrasion: Tiny nicks along
facet junctions, producing white fuzzy lines instead of sharp
crisp facet edges.
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.
Bearded Girdle: If a
diamond is rounded up too quickly in the fashioning process, the
surface of the girdle will lack the smoothness and waxy luster
of a finely turned girdle. Consequently, numerous minute,
hairline fractures extend a short distance into the stone. A
girdle with this appearance is referred to as being “bearded” or
Bezel Facets: The eight
large, four-sided facets on the crown of a round, brilliant-cut
gem, the upper points of which join the table and the lower
points, the girdle. Some diamond cutters further distinguish
four of these as “quoin” or “top-corner” facets.
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,
radiant, princesses, hearts, marquises, and pears all fall
within this category of cut.
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.
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.
Depth Percentage: The depth
of a stone measured from the table to the culet, expressed as a
percentage of the stone’s diameter at the girdle, is a
relationship used in the analysis of the proportions of a
Durability: The durability
of a gem depends both on its hardness and “toughness.” It may be
quite tough but easily scratched, or it may be exceedingly hard
but lack toughness because of easy cleavage. Diamond is highest
on the scale of hardness and, despite it rather easily developed
octahedral cleavage, it is among the toughest of gemstones.
Facet: A plane, polished
surface on a diamond or other gemstone.
Faceting: The operation of
placing facets on a diamond or other gem.
Fancy Cut: Any style of
diamond cutting other than the round brilliant or single cut.
Fancy cuts include the marquise, emerald cut, heart shape, pear
shape, keystone, half moon, kite, triangle, and many others.
Also called the “fancy-shaped” diamond or “modern cut.”
Feather: When the plane of
cleavage or fracture in a diamond is viewed at right angle to
it, the appearance is often reminiscent of a feather. Thus,
cleavage and fractures are often called “feathers.”
Fire: Flashes of different
spectrum colors seen in diamonds and other gemstones as the
result of dispersion.
Fisheye: A diamond whose
pavilion is exceedingly shallow, producing a glassy appearance
and a noticeable dearth of brilliancy.
Flawless: The recommended
term for a diamond without external or internal flaws or
blemishes of any description when viewed by a trained eye under
efficient illumination and under a corrected magnifier of not
less than ten power; binocular magnification under dark-field
illumination is preferred. The American Gem Society advocates
the use of the term “flawless” by its members, while at the same
time denying them the use of the term perfect. The Federal Trade
Commission permits the use of the term “flawless,” but only if a
stone conforms to its definition of the word perfect, without
reference to make or color.
Fluorescence: The property
of changing the wavelength of radiation to one in the visible
range; for example, the visible wavelengths emitted by a
material when excited by invisible radiation (such as X-rays,
ultraviolet rays or cathode rays), as well as by certain visible
wavelengths. It is exhibited by ruby, kunzite, yellow-green
synthetic spinel, some diamonds and opals, and many other
Fracture: The breaking or
chipping of a stone along a direction other than a cleavage
Girdle: The outer edge, or
periphery, of a fashioned stone; the portion that is usually
grasped by the setting or mounting; the dividing line between
the crown and pavilion.
Girdle Facets: The 32
triangular facets that adjoin the girdle of a round
brilliant-cut stone, 16 above and 16 below. Also called upper-
and lower-girdle facets, upper- and lower-break facets, top- and
bottom-half facets, skew facets or cross facets. Facets are
sometimes placed directly on the girdle, in which case the stone
is usually said to have a “faceted girdle,” to have a polished
girdle or to be “girdle faceted.”
Girdle Reflection: When a
diamond has a pavilion that is too shallow or flat, the girdle
is seen reflected in the table.
Girdle Thickness: The width
of the outer edge, or periphery, of a fashioned diamond or other
gemstone. In a rounded style of cutting, such as the round
brilliant or pear shape, the girdle edges, when viewed parallel
to the girdle plane, consist of undulating lines caused by the
intersection of the flat facets with the curved girdle. In such
stones, the girdle thickness is measured across the midpoints of
opposing upper- and lower-girdle facets.
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.
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.
Point: 100th of a carat.
Polish Lines: Tiny parallel
lines left by polishing. Fine parallel ridges confined to a
single facet, caused by crystal structure irregularities, or
tiny parallel polished grooves produced by irregularities in the
Rough Girdle: A grainy or
pitted girdle surface, often with nicks.
Inclusion: A general term
used to refer to any external blemish or internal inclusion or
flaw on or in a fashioned diamond; e.g., a feather, carbon spot,
knot, fissure, scratch, natural, etc. The term “flaw” and
“imperfection” are usually used interchangeably.
Proportions: A term that
meant originally the distribution of the mass of a fashioned
diamond above and below the girdle. Use by diamond men has
broadened its meaning to include the major factors that
determine cutting quality; i.e., total depth as a percentage of
the girdle diameter, table diameter, girdle thickness, facet
angles, symmetry, and even details of finish.
Refraction: The bending of
light rays. The deflection from a straight path suffered by a
ray of light as it passes obliquely from a medium of one optical
density to a medium of a different optical density, as from air
into water or from air into a gemstone. The degree of bending is
related to the change in velocity of light and the angel at
which the light impinges.
Scintillation: The display
of reflections from the polished facets of a gemstone seen by
the observer when either the illuminant, the gemstone or the
observer is in motion—a flashing or twinkling of light from the
Twinning Lines: Visible
line on or with in a fashioned diamond, caused by twinning in
the crystal. Since the orientation on one side of a twin plane
differs from that on the other, the best polishing direction for
one is a poorer one for the other; as a result, a line remains
at the surface. Also called knot lines.