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Jewelry Keyword Glossary
AGS
American Gem Society.
A highly respected independent gemological laboratory founded in 1934
whose expert gemologists grade diamond quality and provide a grading report along with each stone they grade. The American Gem Society has its own rating scale for a diamond’s Cut.
This numbering system ranges from 0 to 10. Here is how it breaks down
on their grading report, which they call their “Diamond Quality
Document”:
AGS Cut Grading Scale
0………………..Ideal
1………………..Excellent
2………………..Very Good
3, 4…………….Good
5, 6, 7………….Fair
8, 9, 10………..Poor
It is
important to note that a grading report provided by any gemological
laboratory is NOT a statement of the monetary value of a particular
stone (like an appraisal), but a professional opinion that evaluates only its quality.
Appraisal
An appraisal is a written estimate of the approximate retail
replacement value of diamond jewelry, which may be used for insurance
coverage or other purposes. It is not the same as a grading report,
which evaluates a diamond’s characteristics (such as cut, clarity,
carat, symmetry, etc.). Grading reports do not provide any suggestion
of monetary value, only quality.
Bar Setting
A bar setting is very similar to a channel setting (see above). Used in
circular bands, a bar setting uses a thin bar of metal to hold the
stones in place on either side, so that each bar has a stone on either
side of it. See also prong setting, bezel setting, channel setting, invisible setting, pavé setting, cluster setting, and tension setting.
Bearding
Bearding is the term given to the very small feathers (small fractures that touch the diamond’s surface) along the edge of a diamond, usually appearing at the girdle, or widest part of the diamond.
Bezel Facet
This is the name given to the facet located on the crown, or top portion of a diamond. Jewelers call this the “kite” facet, because of its shape.
Bezel Setting
A bezel setting holds a diamond in place using a thin band of metal that surrounds the diamond at its middle, or girdle.
It can completely or partially surround the stone, depending on the
style and look desired. This type of setting provides good protection
for the middle and bottom (pavilion) portions of the diamond. See also prong setting, channel setting, bar setting, invisible setting, pavé setting, cluster setting, and tension setting.
Brilliant Cut
A type of round cut in diamonds, giving the stone 57 or 58 facets that
are mathematically devised to produce the greatest brilliance. “Cut”
here really refers more to the diamond’s shape, than its proportions. Click for more on a diamond's cut.
Carat or Carat Weight
Carat Weight is one of the 4Cs. A diamond's weight is measured in Carats, a small unit of measurement equal to 200 milligrams. (Don’t confuse this Carat with the term Karat, which is a measure of the purity of gold). The word carat actually comes from the word carob
(as in carob seeds), which is how ancient cultures measured the weight
of diamonds on their scales. In 1913, however, the weight was
standardized internationally and adapted to the metric system.
Diamonds are most accurately weighed when they are not mounted in a
setting. In fact, gemological laboratories such as the Gemological
Institute of America's (GIA) Gem Trade Laboratory and American Gem Society (AGS)
will only grade diamonds that are unmounted. Each carat is divided into
100 parts called "points." So a 1-carat diamond has 100 points, a ¾
carat has 75 points, etc. Points in a fraction of one carat are
measured within ranges, so that a ¾ carat diamond may have between .69
and .82 points and still be considered a ¾ carat. Here’s a table of
size and weight ranges:
Carat Fractions and Their Decimal Equivalents:
| Fraction |
Decimal Equivalent |
| 1/10 ct |
= |
.09 - .11 |
| 1/8 ct |
= |
.12 - .13 |
| 1/7 ct |
= |
.14 - .15 |
| 1/6 ct |
= |
.16 - .17 |
| 1/5 ct |
= |
.18 - .22 |
| 1/4 ct |
= |
.23 - .28 |
| 1/3 ct |
= |
.29 - .36 |
| 3/8 ct |
= |
.37 - .34 |
| 1/2 ct |
= |
.45 - .58 |
| 5/8 ct |
= |
.59 - .68 |
| 3/4 ct |
= |
.69 - .82 |
| 7/8 ct |
= |
.83 - .94 |
| 1.0 ct |
= |
.98 - 1.05 |
Remember, all diamonds are not created equal. Two diamonds of equal Carat Weight may vary substantially in price due to their Cut, Color and Clarity.
Also, a diamond’s weight can be ‘hidden’ in different parts of the
stone. For example, you can have a well-cut diamond, whose weight is
distributed properly, a diamond that is cut too shallow to make it
wider and heavier, but not the most brilliant, or one that is cut too
deeply, to add weight to the bottom of the stone, again compromising
its ability to radiate maximum brilliance.
The carat weight of a diamond is an extremely important determining
factor in its value. Diamonds are valued on a per-carat basis. For
example, a diamond of exceptionally high quality may sell for $20,000
per carat, while one of lesser quality may sell for $1,000 per carat.
So, a three-carat stone could be $60,000 or $3,000, depending on its
per-carat price. Diamond values also increase disproportionately as the
size of the stone increases. In other words, a two-carat stone will not
necessarily cost twice per carat than a one-carat stone. It could cost
much more, like three times. This is because diamonds are more rare in
larger sizes, so increases in size can mean disproportionate increases
in value. As you take a stone of a particular cut, clarity and color
and move its carat weight to the next price category, you may see quite
a large increase in the price per carat. This jump gets proportionately
larger as the number of carats increases.
Certificate (also known as Grading Report)
Many diamonds are certified by an independent laboratory so purchasers
can feel confident that their diamond is indeed of the quality the
seller represents. The way that diamonds are certified is by having
them evaluated by an independent gemological laboratory with skilled
gemologists who use specialized equipment to measure and evaluate each
diamond’s particular characteristics and attributes. This information
is provided in written form and is called a diamond grading report or
diamond quality document (it is sometimes referred to as a certificate,
which is less accurate).
The diamond’s value is determined primarily by its Cut, Clarity, Color and Carat weight (a.k.a. the 4Cs),
which are the criteria that will be listed on most reports. Generally,
diamonds over .75 carat are sent out for certification. However,
Diamond.com offers grading reports on all stones of 1/3 ct. or more.
Although there are several reputable independent grading laboratories,
the best known is the Gemological Institute of America's (GIA)
Gem Trade Laboratory. The GIA is a non-profit organization whose
functions include gemological education, research and certification.
Some other well-known laboratories include the European Gemological
Laboratories (EGL), the Hoge Raad vor Diamont (HRD), the American Gem Society (AGS)
and the International Gemological Institute (IGI). All diamonds at
Diamond.com of 1/3 ct. or more come with a grading report from one of
these laboratories.
A grading report contains the stone’s color grade, as determined by
comparing it to a set of diamonds of known color. This is listed as a
letter of the alphabet from D through Z, with D, E and F being
completely colorless and having the highest value and Z being yellow in
color and having the lowest value. The report also lists the diamond’s
clarity, an evaluation of any natural 'birthmarks' the stone may have
inside or on its surface. The type and location of these identifying
characteristics determines the clarity grade, and therefore its value.
Clarity grades are:
| F |
Flawless. The diamond shows no inclusions or blemishes of any sort under 10X magnification when observed by an experienced grader. |
| IF |
Internally Flawless.
The diamond has no inclusions when examined by an experienced grader
using 10X magnification, but will have some minor blemishes. |
| VVS1, VVS2 |
Very, Very slightly included. The diamond contains minute inclusions that are difficult even for experienced graders to see under 10X magnification. |
| VS1, VS2 |
Very slightly included.
The diamond contains minute inclusions such as small crystals, clouds
or feathers when observed with effort under 10X magnification. |
| SI1, SI2 |
Slightly included.
The diamond contains inclusions (clouds, included crystals, knots,
cavities, and feathers) that are noticeable to an experienced grader
under 10X magnification. |
| I1, I2, I3 |
Included.
The diamond contains inclusions (possibly large feathers or large
included crystals) that are obvious under 10X magnification and may
affect transparency and brilliance. |
The carat weight of the diamond will also be listed on the grading
report, rounded to the nearest hundredth of a carat (for example 1.25
ct, .76 ct, etc.) Diamond weights are not listed as fractions (1/3,
1/2, etc.) on diamond grading reports, since these values indicate ranges and are not as accurate. The diamond’s measurements (width and height) will also be indicated in millimeters.
A grading report also includes a diagram that “maps” the diamond's inclusions.
These may be listed as “crystals”, “feathers”, “pinpoints” or
“naturals”. Since each diamond is unique, the diagram acts like a
fingerprint to identify that particular diamond. A diamond can be
compared to its grading report by examining it under a 10-power loupe.
Not all laboratories grade a diamond’s cut. The GIA's Gem Trade
Laboratory, for example does not evaluate the quality with which a
diamond has been cut. You will, however find information on its depth- and table percentages, girdle thickness, as well as general comments on the stone’s polish and symmetry.
The AGS does provide an evaluation of a diamond’s cut, listed on a
scale from 0 to 10, with 0 being cut to ‘ideal’ proportions and 10
being cut to less-than-ideal. Other laboratories, may list the cut as
“good”, “very good”, etc. Of course, the diamond’s shape (round, princess, emerald, heart, etc.) will be indicated as part of the description of the diamond.
Grading reports will also list the presence of a diamond’s fluorescence, if any, as well as the actual color that it fluoresces.
It is important to note that a diamond grading
report from an independent laboratory is NOT an appraisal, which
estimates the monetary value of a particular stone. It is simply an
impartial, informed opinion made by an experienced gemologist.
Channel Setting
In a channel setting, two strips of metal (gold, platinum, etc.) hold
the diamond(s) in place at the sides. There is no metal between the
stones. This type of setting protects the girdle area of the diamond,
as well as securing small stones more effectively than a prong setting.
Channel-set diamonds also sit flush with the mounting, making them less
likely to get snagged on other objects, such as hair or clothing. See
also prong setting bezel setting, bar setting, invisible setting, pavé setting, cluster setting, and tension setting.
Clarity
Clarity is one of the 4Cs.
A diamond’s clarity is measured using a jeweler’s loupe (a small
magnifying glass used to view gemstones) under 10-power magnification.
The FTC requires all diamond grading be done under 10-power
magnification; any flaws not detected under this magnification are
considered to be non-existent.
Most diamonds contain some identifying characteristics (crystals,
clouds, or feathers), which can be found inside the stone (called inclusions).
Surface blemishes are not considered a major concern, since they can
often be polished away. Crystals are mineral deposits trapped inside
the diamond; clouds are small specks or hazy areas that give a milky
appearance; and feathers are small cracks that appear to be
feather-shaped.
The size and location of these inclusions and blemishes will determine
the diamond's clarity grade and can have a substantial effect on the
value of the diamond. The accepted GIA grading system for measuring a
diamond’s clarity ranges from "flawless" (F) to "included" (I3), which is very obvious even to the naked eye. Here is an overview of the GIA Clarity Grading Scale:
| F |
Flawless. The diamond shows no inclusions or blemishes of any sort under 10X magnification when observed by an experienced grader. |
| IF |
Internally Flawless.
The diamond has no inclusions when examined by an experienced grader
using 10X magnification, but will have some minor blemishes. |
| VVS1, VVS2 |
Very, Very slightly included. The diamond contains minute inclusions that are difficult even for experienced graders to see under 10X magnification. |
| VS1, VS2 |
Very slightly included.
The diamond contains minute inclusions such as small crystals, clouds
or feathers when observed with effort under 10X magnification. |
| SI1, SI2 |
Slightly included.
The diamond contains inclusions (clouds, included crystals, knots,
cavities, and feathers) that are noticeable to an experienced grader
under 10X magnification. |
| I1, I2, I3 |
Included.
The diamond contains inclusions (possibly large feathers or large
included crystals) that are obvious under 10X magnification and may
affect transparency and brilliance. |
A truly flawless diamond is extremely rare. In fact, it’s more
important that any blemishes or inclusions do not affect the stone’s
attractiveness or durability, than that the diamond is ‘perfect’. It is
these identifying characeristics that give each stone its individual
character, or fingerprint, making your diamond as unique as you are. As
a matter of fact, these distinguishing marks are mapped on a diamond
grading report (if your stone came with one), enabling you to identify
your stone if need be.
Since clarity in a diamond is so critical, it will of course result in
price differences. If a diamond of a particular cut, color and carat
weight is moved to the next clarity grade, it’s possible to see a
significant increase or decrease in the per-carat price--all other
factors being equal. See Clarity in our Learning Center for more information.
Cloud
Clouds are a type of inclusion found in some diamonds. They are usually
small specks or hazy areas that give the diamond a milky appearance.
Clouds are usually indicated on diamond grading reports. The location
and size of the clouds may have a direct bearing on the diamond’s
value. See also feather, crystal.
Cluster Setting
In a cluster setting, several stones are mounted together in a group,
for a cluster effect. It is frequently seen with several small stones
surrounding a central, larger stone. See also prong setting , bezel setting , channel setting , bar setting , invisible setting , pavé setting and tension setting.
Color
Color is one of the 4Cs.
The most important thing to know about color is, in general, the less
of it a diamond has, the more valuable it is, all other factors being
equal. This is because the less color a diamond itself has, the more
purely it can refract the light that enters it, making it sparkle with
brilliance and fire. Diamond colors range from colorless to slightly
yellow or brown, to more rare and costly pink, green or blue stones
(commonly referred to as “fancy” diamonds). Excluding “fancy” diamonds,
the ideal color for a diamond is colorless, although this is extremely
rare.
Color is evaluated by comparing it to the
Gemological Institute of America’s (GIA) color scale, which rates the
visible amount of body color as seen through the side of the diamond. A
diamond’s color is most accurately determined when it is not mounted in
a setting, since settings can add tints of their own color into the
diamond. This is more evident in yellow gold settings, and less so in
white gold and platinum settings. Even a trained professional can’t
always tell the difference between close grades of color in a diamond
if it is still mounted in a setting. For this reason, gemological
laboratories such as the Gemological Institute of America's (GIA) Gem Trade Laboratory and American Gem Society (AGS) will only grade diamonds that are unmounted.
The color grading system for diamonds uses the letters of the alphabet
from D through Z. Each letter represents a different range of color.
(See illustration below) Diamonds with a color grade of D, E or F are
considered colorless (and are therefore the most valuable, all other
factors being equal); G, H, I and J are near colorless; K, L and M have
a faint yellow tint; N, O, P, Q and R have a very light yellow tint and
S, T, U, V, W, X, Y and Z are light yellow. It’s important to
understand that color alone does not determine the value of a diamond.
Its value is based on a number of factors, most important of which are
the 4Cs--cut, color, clarity and carat weight. A diamond of D color
that has imperfections or is poorly cut is not as valuable as a stone
of a lower color grade that has a superior Cut and Clarity.
Diamonds can have a color
grade as low as X, Y and Z. These diamonds will have a visibly yellow
color and are considered less desirable than diamonds with a D, E or F
color grading. If a diamond’s color is more intense than “Z”, it is
considered “fancy”. Fancy diamonds garner higher prices than even light
yellow diamonds.
A diamond’s color also has a great impact on its cost. Since lack of
color is the most sought-after trait in terms of color, diamonds that
are higher up on the color scale (e.g. D, E, F) will have greater
value. As a diamond with a specific cut, carat and clarity is moved up
each color grade, the per-carat cost for the stone will also increase.
See “Color” in our Learning Center for more information.
Crown
The crown is the top section of a diamond, above its widest point, or girdle, that comprises the table, and the star-, bezel- and upper-girdle facets. See illustration at the top of this page.
Crown Angle
The crown angle of a diamond is a measurement of the angle, in degrees, that is formed by the facets of the upper portion, or crown of the stone. The distance from the girdle (widest point) to the table (the flat facet at the top of the stone) determines whether the crown will be thick, thin or proportionally ‘ideal’.
Therefore, the higher the crown, the steeper the crown angle will be;
the thinner the crown, the shallower the crown angle will be. The
angles at which the crown and pavilion facets (those facets below the girdle) are cut directly affects the
diamond’s ability to refract light rays, which is what gives a diamond
its remarkable fire and brilliance.
Crystal
A crystal is a type of inclusion
found in some diamonds. It is simply a mineral deposit that has been
trapped inside the diamond. Crystals are usually indicated on diamond grading reports. The location and size of the crystal may have a direct bearing on the diamond’s value. See also feather, cloud.
Culet
The point on the bottom of a diamond's pavilion is called its culet. On some diamonds, the culet is actually formed into a facet;
in others, it is formed into a point. Round diamonds can therefore have
either 58 or 57 facets, depending on whether the culet has been faceted
or not.
Cut
Cut is one of the 4Cs.
The only one of the 4Cs that is within human's control, cut refers to
the geometric proportions to which a diamond is crafted (usually by a
master diamond cutter with many years of experience). Once the
diamond’s shape has been determined, facets are cut. It is these facets
that refract light like a prism and produce the stone’s fire and
brilliance.
There are many factors that go into a well-cut diamond. It must be cut
to precise proportions and angles; it cannot be too shallow or too
deep; its facets must align properly; its surfaces must be polished to
a mirror-like finish. Many of these characteristics are graded on what
is known as a diamond grading report, which is created by an independent gemological laboratory and is provided with many diamonds.
An “ideal cut” is a specific set of guidelines that delineate the
proportions that give a diamond the highest amount of fire and
brilliance. The concept of an ‘ideal cut’ diamond originated with a
diamond cutter and mathematician named Marcel Tolkowsky, in his
dissertation on the subject in 1919. Sometimes called the “Father of
the American Brilliant Cut”, Tolkowsky was the first person to show
that a diamond with 58 facets that was cut to specific proportions
would result in the highest possible fire and brilliance.
Although the proportions of an ideal cut vary depending on which source
you talk to (from jeweler to jeweler, country to country), there are
certain ranges that are generally accepted as capable of evoking the
most desirable fire and brilliance from a stone. These ranges must
cause the light entering the diamond to be reflected and dispersed
through the table (top), not through the sides or bottom. The ideal cut
diamond possesses good symmetry, i.e. its table and girdle are parallel to each other and the culet and table are well centered (see diagram below). The facets are also well aligned and symmetrical. Of course, ideal cut diamonds must have excellent polish and high luster.
But most of all, an ideal cut diamond must be cut to bring out the
stone’s brilliance and fire, not retain the most weight from the rough
cut stone. It should not have a crown or pavilion that is too shallow
or excessively deep. The girdle should not be too thin, or the stone
may chip. If it is too thick, its brilliance may be reduced. If the
girdle appears to be a wide band around the diamond, it’s probably also
too thick. If you can hardly see it, it’s probably too thin. A properly
cut girdle should be even all the way around.
It’s important to note that some independent grading laboratories do
not grade a diamond’s cut, while others do. The Gemological Institute
of America's (GIA)
Gem Trade Laboratory, for example, does not give an evaluation of the
quality of a diamond’s cut, only the shape and measurements of the
stone. It does, however, give the proportions of the diamond (depth and
table percentages, girdle thickness, culet size (if any) as well as a
general rating of the stone’s finish, including its polish and symmetry. The American Gem Society (AGS)
on the other hand, has its own rating scale for a diamond’s Cut. This
numbering system, ranges from 0 to 10, with 0 being “ideal” and 10
being less-than-ideal:
0………………..Ideal
1………………..Excellent
2………………..Very Good
3, 4…………….Good
5, 6, 7………….Fair
8, 9, 10………..Poor
A diamond’s cut is a complicated evaluation based on many factors, including depth and table percentages, crown angles, girdle thickness
and others. Added to that, some independent grading laboratories do not
grade cut, making the determination even harder to quantify. We can,
however, tell you that an ideal cut diamond generally garners a 20 to
30% higher price than one that is just “good”. See “Cut” in our Learning Center for more information.
Depth
A diamond’s depth is the distance from the Table (top) to its Culet (bottom).
Depth Percentage
Depth percentage is the measurement of a diamond’s depth, relative to its diameter. A diamond’s depth is measured from its table (top) to its culet (bottom). Its width is measured at its widest point, called its girdle.
This depth-to-width relationship is largely responsible for the
diamond’s being properly proportioned, resulting in the proper
refraction of light and maximum fire and brilliance. Depth percentage
is often indicated on diamond grading reports.
Since a well-cut diamond should have even brilliance throughout the
stone, its depth percentage is probably the best indicator of a
diamond’s cut. If the stone has a dark center, then the depth of the
diamond’s pavilion is probably too great, letting light escape out the
sides of the stone, instead of out the top (sometimes called a
‘nailhead’ by jewelers). If it has a ring-like shadow when viewed
through the top (sometimes called a ‘fisheye’ by jewelers), the diamond’s pavilion is probably too shallow. Shallow pavilions can also cause a diamond to look watery and lifeless.
Diamond
The simplest of all the gemstones, diamond consists of pure
crystallized carbon. A diamond begins to crystallize far beneath the
earth's surface among a mixture of liquids, gases, and crystals.
Diamonds can be from 1 to 3 billion years old--more than two-thirds the
age of the Earth itself. Diamond is also the hardest substance known to
man. In fact, it can only be cut and polished by another diamond.
Despite its hardness, however, it is not indestructible. If a diamond
is struck at the right angle, it can chip or break. Visit our Learning Center for more on diamonds.
EGL
European Gemological Laboratory.
Established in 1974, the EGL is a well-respected independent laboratory
with offices in Antwerp, New York, Los Angeles, Johannesburg, Paris,
Israel and Seoul whose trained gemologists grade diamond quality and
provide a diamond grading report
along with each stone they grade. The EGL does not sell diamonds, but
acts as a consultant in the grading of precious gems, as well as
providing educational courses in diamonds and diamond grading.
It
is important to note that a grading report provided by any gemological
laboratory is NOT a statement of the monetary value of a particular
stone (like an appraisal), but a professional opinion that evaluates only its quality.
External Reflection
A diamond’s polish is a good indication of the diamond cutter’s skill
and attention to detail. The finer the polish, the brighter and more
lustrous the diamond will be. While the primary light refraction that
causes a diamond’s fire and brilliance occurs inside its facets (called
internal refraction), some of the light rays are reflected back to the
viewer’s eye from the surface of the stone itself. This is known as external reflection. Finely polished diamonds should display a high degree of external reflection.
Eye-Clean
Eye-clean is an expression that jewelers use to designate a gem whose flaws or inclusions cannot be detected without a loupe.
Facet
Facets are the flat planes or surfaces on a diamond. Each facet must be cut in exact geometric relation to the others to create the most fire and brilliance.
Feather
A feather is a type of inclusion that occurs naturally in diamonds.
Feathers are simply small fractures, shaped like a bird's feather, that
touch the stone’s surface. They are indicated on a diamond grading report that is provided with many diamonds.
Fluorescence
A characteristic in some diamonds that can affect a its value is known
as fluorescence. When exposed to ultraviolet light, small percentages
of diamonds fluoresce, or emit light. Fluorescence does not necessarily
affect a diamond’s value, however it is listed on a diamond grading report.
Grades can be None, Faint, Slight, Medium, Strong or Extreme. Some
reports also list the color of the fluorescence (e.g. blue, yellow,
white, etc.). Some stones that give off blue light may actually be more
valuable, since it can make them appear “whiter” in daylight or
fluorescent lighting.
GIA
Gemological Institute of America.
Established in 1931 as the nonprofit educational resource for the gem
and jewelry industry, the GIA is the universally accepted authority on
diamonds. The GIA's Gem Trade Laborarory is an independent lab whose
trained gemologists grade diamond quality and provide a diamond grading report along with each stone.
It
is important to note that a grading report provided by any gemological
laboratory is NOT a statement of the monetary value of a particular
stone (like an appraisal), but a professional opinion that evaluates only its quality.
Girdle
The girdle is the outermost edge of a diamond that sits in the setting,
separating the upper and lower sections of the stone. It can vary in
thickness, depending on how it was faceted by a cutter during
manufacturing.
Girdle Thickness
A diamond’s girdle,
or outermost edge that separates the upper and lower sections of the
stone, can vary in thickness depending on how it was faceted by a
cutter during manufacturing. Ideally, the girdle should not be too
thin, or the stone may chip. If it is too thick, its brilliance may be
reduced. If the girdle appears to be a wide band around the diamond,
it’s probably too thick, also. If you can hardly see it, it’s probably
too thin. A properly cut girdle should be even all the way around.
Grading Report (also called a Certificate)
Many diamonds are certified by an independent laboratory, so purchasers
can feel confident that their diamond is indeed of the quality the
seller represents. The way that diamonds are certified is by having
them evaluated by an independent gemological laboratory with skilled
gemologists who use specialized equipment to measure and evaluate each
diamond’s particular characteristics and attributes. This information
is provided in written form and is called a diamond grading report or
diamond quality document (it is sometimes referred to as a certificate,
which is less accurate).
The diamond’s value is determined primarily by its Cut, Clarity, Color and Carat weight (a.k.a. the 4Cs),
which are the criteria that will be listed on most reports. Generally,
diamonds over .75 carats are sent out for certification. .
Although there are several reputable independent grading laboratories,
the best known is the Gemological Institute of America's (GIA)
Gem Trade Laboratory. The GIA is a non-profit organization whose
functions include gemological education, research and certification.
Some other well-known laboratories include the European Gemological
Laboratories (EGL), the Hoge Raad vor Diamont (HRD), the American Gem Society (AGS)
and the International Gemological Institute (IGI). Most diamonds at
Diamond.com come with a certificate from one of these laboratories.
A grading report contains the stone’s color grade, as determined by
comparing it to a set of diamonds of known color. This is listed as a
letter of the alphabet from D through Z, with D, E and F being
completely colorless and having the highest value and Z being yellow in
color and having the lowest value. It also lists the diamond’s clarity,
an evaluation of any natural blemishes or inclusions the stone may have
inside or on its surface. The type and location of these blemishes
determines the clarity grade, and therefore its value. Clarity grades
are:
| F |
Flawless. The diamond shows no inclusions or blemishes of any sort under 10X magnification when observed by an experienced grader. |
| IF |
Internally Flawless.
The diamond has no inclusions when examined by an experienced grader
using 10X magnification, but will have some minor blemishes. |
| VVS1, VVS2 |
Very, Very slightly included. The diamond contains minute inclusions that are difficult even for experienced graders to see under 10X magnification. |
| VS1, VS2 |
Very slightly included.
The diamond contains minute inclusions such as small crystals, clouds
or feathers when observed with effort under 10X magnification. |
| SI1, SI2 |
Slightly included.
The diamond contains inclusions (clouds, included crystals, knots,
cavities, and feathers) that are noticeable to an experienced grader
under 10X magnification. |
| I1, I2, I3 |
Included.
The diamond contains inclusions (possibly large feathers or large
included crystals) that are obvious under 10X magnification and may
affect transparency and brilliance. |
The carat weight of the diamond will also be listed on the grading
report, rounded to the nearest hundredth of a carat (for example 1.25
ct, .76 ct, etc.) Diamond weights are not listed as fractions (1/3,
1/2, etc.) on diamond grading reports, since these values indicate ranges and are not as accurate. The diamond’s measurements (width and height) will also be indicated in millimeters.
A grading report also includes a diagram that “maps” the diamond's inclusions.
These may be listed as “crystals”, “feathers”, “pinpoints” or
“naturals”. Since each diamond is unique, the diagram acts like a
fingerprint to identify that particular diamond. A diamond can be
compared to its grading report by examining it under a 10-power loupe.
Not all laboratories grade a diamond’s cut. The GIA's Gem Trade
Laboratory, for example does not evaluate the quality with which a
diamond has been cut. You will, however find information on its depth and table percentages, girdle thickness, as well as general comments on the stone’s polish and symmetry.
The AGS does provide an evaluation of a diamond’s cut, listed on a
scale from 0 to 10, with 0 being cut to ‘ideal’ proportions and 10
being cut to less-than-ideal. Other laboratories may list the cut as
“good”, “very good”, etc. Of course, the diamond’s shape (round, princess, emerald, heart, etc.) will be indicated as part of the description of the diamond.
Grading reports will also list the presence of a diamond’s fluorescence, if any, as well as the actual color that it fluoresces.
It is important to note that a diamond grading
report from an independent laboratory is NOT an appraisal, which
estimates the monetary value of a particular stone. It is simply an
impartial, informed opinion made by an experienced gemologist.
It is important to note that a grading report
provided by any gemological laboratory is NOT a statement of the
monetary value of a particular stone (like an appraisal), but a professional opinion that evaluates only its quality.
Ideal Cut
An “ideal cut” is a specific set of guidelines that delineate the
proportions that give a diamond the highest amount of fire and
brilliance. The concept of an ‘ideal cut’ diamond originated with a
diamond cutter and mathematician named Marcel Tolkowsky, in his
dissertation on the subject in 1919. Sometimes called the “Father of
the American Brilliant Cut”, Tolkowsky was the first person to show
that a diamond with 58 facets that was cut to specific proportions
would result in the highest possible fire and brilliance.
Although the proportions of an ideal cut vary depending on which source
you talk to (from jeweler to jeweler, country to country), there are
certain ranges that are generally accepted as capable of evoking the
most desirable fire and brilliance from a stone. These ranges must
cause the light entering the diamond to be reflected and dispersed
through the table (top), not through the sides or bottom. The ideal cut
diamond possesses good symmetry, i.e. its table and girdle are parallel
to each other and the culet and table are well centered (see diagram
below). The facets are also well aligned and symmetrical. Of course,
ideal cut diamonds must have excellent polish (and therefore high
luster).
But most of all, an ideal cut diamond must be cut to bring out the
stone’s brilliance and fire, not retain the most weight from the rough
cut stone. It should not have a crown or pavilion that is too shallow
or excessively deep. The girdle should not be too thin, or the stone
may chip. If it is too thick, its brilliance may be reduced. If the
girdle appears to be a wide band around the diamond, it’s probably also
too thick. If you can hardly see it, it’s probably too thin. A properly
cut girdle should be even all the way around.
IGI
International Gemological Institute.
One of the largest, most respected gemological institutions in the
world. The IGI is an independent laboratory whose trained gemologists
grade diamond quality and provide a grading report
along with each stone they grade. The EGL does not sell diamonds, but
acts as a consultant in the grading of precious gems, as well as
providing educational courses in diamonds and diamond grading. Founded
in Antwerp in 1975, the IGI has offices in Antwerp, New York, Bangkok
and Mumbai.
It is important to note that a grading report
provided by any gemological laboratory is NOT a statement of the
monetary value of a particular stone (like an appraisal), but a professional opinion that evaluates only its quality.
Inclusion
A small cloud, feather, crystal
or other identifying characteristic that occurs naturally in diamonds.
The fewer inclusions, the more rare the diamond and the greater its
value, all other factors being equal. A truly flawless diamond is
extremely rare.
Invisible Setting
Invisible-set diamonds are placed very closely together, with the metal
concealed underneath the diamonds, giving them the appearance of a
continuous, uninterrupted surface. Since the metal of the setting is
not seen, this type of setting is an excellent way to showcase the
brilliance of the diamonds themselves. It also allows an increased
amount of light to enter the stone (and, thus give off more
brilliance), since there are no prongs or bezels impeding the light’s entry. See also prong setting , bezel setting , channel setting , bar setting , pavé setting , cluster setting and tension setting.
Length-to-Width Ratio
In stones with shapes other than round (such as marquise, pear, hearts,
etc.), the length-to-width ratio is the relationship between the length
of its shorter and longer dimensions.
Loupe
A loupe is a small magnifying glass used to view gemstones.
Usually 10x, or ten-power, magnification. The FTC requires all diamond
grading be done under 10-power magnification; any flaws not detected
under this magnification are considered to be non-existent.
Mohs Scale
The Mohs scale is a table of relative hardness that ranks a mineral's
strength and durability on a scale from 1 to 10, with 1 being talc and
10 being diamond. Developed over 100 years ago by Frederic Mohs.
Mounting (or Setting)
The setting is the part of a ring that holds the diamond(s) in place.
It is usually made of gold or platinum. Here is an overview of several
of the most popular styles of settings:
Prong Setting
In a prong setting, the diamond is held in place by a number of metal
prongs, which rise above the main body of the ring and are bent over
the stone to hold it in place. The number of prongs varies according to
the stone’s shape, as does their height above the main body of the ring.
Bezel Setting
A bezel setting holds a diamond in place using a thin band of metal that surrounds the diamond at its middle, or girdle.
It can completely or partially surround the stone, depending on the
style and look desired. This type of setting provides good protection
for the middle and bottom (pavilion)
portions of the diamond. Bezel settings can have straight or scalloped
edges, an can be molded to accommodate many shapes of stones.
Channel Setting
In a channel setting, two strips of metal (gold, platinum, etc.) hold
the diamond(s) in place at the sides, with no metal between the stones.
This type of setting protects the girdle area of the diamond, as well
as securing small stones more effectively than a prong setting.
Channel-set diamonds also sit flush with the mounting, making them less
likely to get snagged on other objects, such as hair or clothing.
Bar Setting
A bar setting is very similar to a channel setting (see above). Used in
circular bands, a bar setting uses a thin bar of metal to hold the
stones in place on either side, so that each bar has a stone on either
side of it.
Invisible Setting
Invisible-set diamonds are placed very closely together, with the metal
concealed underneath the diamonds, giving them the appearance of a
continuous, uninterrupted surface. Since the metal of the setting is
not seen, this type of setting is an excellent way to showcase the
brilliance of the diamonds themselves. It also allows an increased
amount of light to enter the stone (and, thus give off more
brilliance), since there are no prongs or bezels impeding the light’s
entry.
Pavé Setting
In pavé setting, diamonds are fit into small holes and set almost level
with the surface of the ring. They are set in rows, with no metal
between them, giving the appearance of the diamonds having been paved
(Pavé is French for paved), like a cobblestone road.
Tiffany Setting
Very popular in bridal rings, this four- or six-prong style is called a “Tiffany” setting, because it was originally developed by the founder
of Tiffany & Co. in 1886. A prong setting allows the most light to
enter the diamond from all angles, maximizing its brilliance. Six
prongs also provide added security.
Pavé Setting
In pavé setting, diamonds are fit into small holes and set almost level
with the surface of the ring. They are set in rows, with no metal
between them, giving the appearance of the diamonds having been paved
(Pavé is French for paved), like a cobblestone road. See also prong setting , bezel setting , channel setting , bar setting , invisible setting , cluster setting and tension setting.
Pavilion
The pavilion of a diamond is the lower part (below the girdle, or widest point) that comprises the Lower Girdle Facet, Pavilion Main Facet and Culet.
Points
Each carat in a diamond’s weight is divided into 100 parts, called 'points.' A
1-Carat diamond has 100 points, a 3/4 Carat has 75 points, etc. Points
in a fraction of one carat are measured within ranges, so that a 3/4
Carat diamond may have between .69 and .82 points and still be
considered a 3/4 carat. Here’s a table of size and weight ranges:
Carat Fractions and Their Decimal Equivalents:
| Fraction |
Decimal Equivalent |
| 1/10 ct |
= |
.09 - .11 |
| 1/8 ct |
= |
.12 - .13 |
| 1/7 ct |
= |
.14 - .15 |
| 1/6 ct |
= |
.16 - .17 |
| 1/5 ct |
= |
.18 - .22 |
| 1/4 ct |
= |
.23 - .28 |
| 1/3 ct |
= |
.29 - .36 |
| 3/8 ct |
= |
.37 - .34 |
| 1/2 ct |
= |
.45 - .58 |
| 5/8 ct |
= |
.59 - .68 |
| 3/4 ct |
= |
.69 - .82 |
| 7/8 ct |
= |
.83 - .94 |
| 1.0 ct |
= |
.98 - 1.05 |
Polish
A diamond’s polish is a good indication of the diamond cutter’s skill
and attention to detail. The finer the polish, the brighter and more
lustrous the diamond will be. While the primary light refraction that
causes a diamond’s fire and brilliance occurs inside its facets (called
internal refraction), some of the light rays are reflected back to the
viewer’s eye from the surface of the stone itself. This is known as
external reflection. Finely polished diamonds should display a high
degree of external reflection.
On diamond grading reports, such as those provided by the American Gemological Society (AGS), polish is rated as excellent, very good, good, fair or poor.
Prong
A prong is one of several claw-like wires that are bent over a diamond to hold a it in place in a setting.
Prong Setting
In a prong setting, the diamond is held in place by a number of metal
prongs, which rise above the main body of the ring and are bent over
the stone to hold it in place. The number of prongs varies according to
the stone’s shape, as does their height above the main body of the
ring. See also bezel setting , channel setting , bar setting , invisible setting , pavé setting , cluster setting and tension setting.
Setting (or Mounting)
The setting is the part of a ring that holds the diamond(s) in place.
It is usually made of gold or platinum. Here is an overview of several
of the most popular styles of settings:
Prong Setting
In a prong setting, the diamond is held in place by a number of metal
prongs, which rise above the main body of the ring and are bent over
the stone to hold it in place. The number of prongs varies according to
the stone’s shape, as does their height above the main body of the ring.
Bezel Setting
A bezel setting holds a diamond in place using a thin band of metal that surrounds the diamond at its middle, or girdle.
It can completely or partially surround the stone, depending on the
style and look desired. This type of setting provides good protection
for the middle and bottom (pavilion)
portions of the diamond. Bezel settings can have straight or scalloped
edges, an can be molded to accommodate many shapes of stones.
Channel Setting
In a channel setting, two strips of metal (gold, platinum, etc.) hold
the diamond(s) in place at the sides, with no metal between the stones.
This type of setting protects the girdle area of the diamond, as well
as securing small stones more effectively than a prong setting.
Channel-set diamonds also sit flush with the mounting, making them less
likely to get snagged on other objects, such as hair or clothing.
Bar Setting
A bar setting is very similar to a channel setting (see above). Used in
circular bands, a bar setting uses a thin bar of metal to hold the
stones in place on either side, so that each bar has a stone on either
side of it.
Invisible Setting
Invisible-set diamonds are placed very closely together, with the metal
concealed underneath the diamonds, giving them the appearance of a
continuous, uninterrupted surface. Since the metal of the setting is
not seen, this type of setting is an excellent way to showcase the
brilliance of the diamonds themselves. It also allows an increased
amount of light to enter the stone (and, thus give off more
brilliance), since there are no prongs or bezels impeding the light’s
entry.
Pavé Setting
In pavé setting, diamonds are fit into small holes and set almost level
with the surface of the ring. They are set in rows, with no metal
between them, giving the appearance of the diamonds having been paved
(Pavé is French for paved), like a cobblestone road.
Tiffany Setting
Very popular in bridal rings, this four- or six-prong style is called a “Tiffany” setting, because it was originally developed by the founder
of Tiffany & Co. in 1886. A prong setting allows the most light to
enter the diamond from all angles, maximizing its brilliance. Six
prongs also provide added security.
Shape
Diamonds are available in nine shapes: round (also called brilliant or
full-cut), marquise, pear, oval, princess, heart, pear, emerald and
asscher. Which shape you choose is purely a matter of personal
preference. Don’t confuse a diamond’s shape with its Cut, which is an evaluation of the diamond’s proportions (and one of the 4Cs).
Of course, the most popular and commonly seen shape for diamonds is the
round or brilliant cut, which has 57 or 58 facets (depending on whether
the culet , or point at the bottom of the stone, is faceted or not). It’s the
‘classic’ shape that most people think of when they think of a diamond.
Often considered the ideal shape for a diamond, the round cut was first
perfected by a diamond cutter and mathematician named Marcel Tolkowsky,
in his dissertation on the subject in 1919. Sometimes called the
“Father of the American Brilliant Cut”, Tolkowsky was the first person
to show that a diamond with 58 facets that was cut to specific
proportions would result in the highest possible fire and brilliance.
Over time, it became clear that it was not cost-effective to cut each
and every diamond to these stringent requirements, since it resulted in
lost diamond weight, and appears smaller to the eye than a ‘standard’ cut of the same weight. Click here for a more detailed discussion of cut.
But the round cut is by far not your only choice. All shapes are
capable of fantastic fire and brilliance. The only difference is the
result of the diamond cutter’s decision to cut the rough diamond into
that particular shape.
When diamonds are mined, they are not in the same shape we see in the
finished product. The ‘roughs’ are examined during a process known as
marking, in which a planner decides how to get the greatest size,
fewest inclusions and highest brilliance from the finished stone. Since
diamonds are so rare and valuable, it is critical that there the
smallest amount of material is wasted during the manufacturing process
(Click here for more details on diamond manufacturing).
Symmetry
Part of a diamond’s overall finish, symmetry is critical to a diamond’s
ability to refract light, as well as its value. In order to have good
symmetry, a diamond’s facets must be cut exactly to specific
mathematical proportions (See Ideal Cut).
Symmetry describes several factors: how the facet edges align each
other; whether the corresponding facets from opposite sides of the
diamond align with each other or not; and whether the facets from the crown, or top of the diamond are properly aligned with the corresponding ones on the bottom (pavilion). When choosing a diamond, look for Excellent, Very Good or Good ratings on the grading report, if symmetry is graded.
Table
The table is the name given to the large, flat facet on the top of a diamond.
Table Percentage
A diamond’s table percentage is a measurement of its table width, relative to the width of the entire stone (at its girdle,
or widest point). This relationship is critical for maximum fire and
brilliance: too small or too large a table can hamper the diamond’s
ability to disperse light properly, not to mention poss
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