Don't know a culet from a pavilion when it comes to diamonds? Don't worry. We've put together a comprehensive glossary to help you understand these sometimes-technical terms. Just click the first letter of the word you're looking for and you'll get a clear, concise definition.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
4C's
Diamonds are graded and priced according to what is universally referred to as the “4C’s”. They are Cut, Color, Clarity and Carat Weight. Here is an explanation of each of the 4Cs:
Cut
The only quality of a diamond that is within man’s control is its cut. 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. Here is an illustration of how a diamond handles light:
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 57 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 Diamond Proportions 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 (GIA), 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 Gemological Society
(AGS) on the other hand, has its own rating scale for a diamond’s cut.
This numbering system ranges from 0 to 10:
AGS Cut Grading Scale
AGS Cut Grading Scale
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 has a 20 to 30% higher value than one that
is just “good”.
Color
The most important thing to know about color is--the less of it a diamond has, the more valuable it is. 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 color scale (called Master Stones), 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 (GIA) and American Gemological 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 grade of color. (See Diamond Color Scale illustration below) Diamonds with a color grade of D, E or F are considered colorless; 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. A diamond that is a D color is absolutely colorless, and is therefore the most valuable. However, 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.
A diamond’s color also has a great impact on its value. Since ‘colorlessness’ is the most sought-after trait in terms of color, diamonds that are higher up on the color scale (e.g. D, E, F) are more valuable. If a diamond of a particular cut, clarity and carat weight is moved to the next color grade, it’s possible to see a significant increase or decrease in the per-carat price--all other factors being equal.
Clarity
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 natural blemishes (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 had no internal or external flaws |
| IF | Internally Flawless; no flaws inside the stone, minor surface blemishes |
| VVS1, VVS2 | Very, Very Small inclusions |
| VS1, VS2 | Very Small inclusions |
| SI1, SI2 | Small Inclusions |
| I1 | Inclusions are easy to locate and may be visible to the naked eye |
| I2 | Inclusions are obvious and are visible to the naked eye |
| I3 | Inclusions are very obvious |
Since clarity, or the measure of blemishes 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.
Carat Weight
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.) Diamonds are most accurately weighed when they are not mounted in a setting. In fact, gemological laboratories such as the Gemological Institute of America (GIA) and American Gemological 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:
Points Conversion
| Fraction | Decimal Equivalent | |
| 1/10 | = | .09 - .11 |
| 1/8 | = | .12 - .13 |
| 1/7 | = | .14 - .15 |
| 1/6 | = | .16 - .17 |
| 1/5 | = | .18 - .22 |
| 1/4 | = | .23 - .28 |
| 1/3 | = | .29 - .36 |
| 3/8 | = | .37 - .44 |
| 1/2 | = | .45 - .58 |
| 5/8 | = | .59 - .68 |
| 3/4 | = | .69 - .82 |
| 7/8 | = | .83 - .94 |
| 1.0 | = | .95 - 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 (See Cut), 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.
A
AGS
American Gemological 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 Gemological 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.
B
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.
C
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 (GIA) and American Gemological 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 | = | .09 - .11 |
| 1/8 | = | .12 - .13 |
| 1/7 | = | .14 - .15 |
| 1/6 | = | .16 - .17 |
| 1/5 | = | .18 - .22 |
| 1/4 | = | .23 - .28 |
| 1/3 | = | .29 - .36 |
| 3/8 | = | .37 - .44 |
| 1/2 | = | .45 - .58 |
| 5/8 | = | .59 - .68 |
| 3/4 | = | .69 - .82 |
| 7/8 | = | .83 - .94 |
| 1.0 | = | .95 - 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 (GIA). 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 Gemological Society (AGS) and the International Gemological Institute
(IGI). All diamonds at Diamond.com of 1/3 ct. or more 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 Master Stones. This is listed as a letter
of the alphabet from D through Z, with D 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 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 has no internal or external flaws |
| IF | Internally Flawless; no flaws inside the stone, minor surface blemishes |
| VVS1, VVS2 | Very, Very Small inclusions |
| VS1, VS2 | Very Small inclusions |
| SI1, SI2 | Small Inclusions |
| I1 | Inclusions are easy to locate and may be visible to the naked eye |
| I2 | Inclusions are obvious and are visible to the naked eye |
| I3 | Inclusions are very obvious |
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 certificate by examining it under a 10-power
loupe.
Not all laboratories grade a diamond’s cut. The GIA, 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, like the AGS, 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 blemishes (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 has no internal or external flaws |
| IF | Internally Flawless; no flaws inside the stone, minor surface blemishes |
| VVS1, VVS2 | Very, Very Small inclusions |
| VS1, VS2 | Very Small inclusions |
| SI1, SI2 | Small Inclusions |
| I1 | Inclusions are easy to locate and may be visible to the naked eye |
| I2 | Inclusions are obvious and are visible to the naked eye |
| I3 | Inclusions are very obvious |
A truly flawless diamond is extremely rare. In fact, it’s more important that any blemishes do not affect the stone’s attractiveness or durability, than that the diamond is ‘perfect’. It is these inclusions 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, or the measure of blemishes 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.
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--the less of it a diamond has, the more valuable it is. 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 color scale (called Master Stones), 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 (GIA) and American Gemological 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 grade of color. (See illustration below) Diamonds with a color grade of D, E or F are considered colorless; 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. A diamond that is a D color is absolutely colorless, and is therefore the most valuable. However, 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.
Because D, E and F are the highest color grade for diamonds, they are also the most valuable. 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. A diamond with a “D” color is considered to be colorless, and is therefore the most valuable. 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 ‘colorlessness’ 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.
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 quality of a diamond that is within human 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 57 facets that was cut to specific proportions would result in the highest possible fire and brilliance. His specific requirements included a 53% table percentage, 16.2% crown height, 43.1% depth percentage, no culet and an extremely thin, or “knife-edge” girdle. 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.
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.
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 57 facets that was cut to specific proportions would result in the highest possible fire and brilliance. His specific requirements included a 53% table percentage, 16.2% crown height, 43.1% depth percentage, no culet and an extremely thin, or “knife-edge” girdle. 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.
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.
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”.
D
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. Here are standards for an Ideal Cut diamond:
Ideal Cut
| SHAPE | TABLE PERCENTAGE | DEPTH PERCENTAGE |
| Round | 53% - 57% | 59% - 62% |
| Radiant | 66% - 70% | 64% - 68% |
| Emerald | 60% - 64% | 63% - 66% |
| Marquise | 56% - 60% | 59.5% - 64.0% |
| Oval | 56% - 60% | 60% - 64% |
| Pear | 56% - 60% | 60% - 64% |
| Princess | 66% - 70% | 64% - 68% |
| Heart | 55% - 62% | 50% - 55% |
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, called Kimberlite magma (after the city of Kimberly, South Africa, where they were discovered in the 1870s). Since Kimberlite is lighter than surrounding rocks, it rises as gases form the earth's mantle and creates carrot-shaped pipes through which diamonds reach the earth's surface. 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.
E
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.
F
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.
G
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. It is an independent laboratory 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 (GIA). 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 Gemological 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 Master Stones. This is listed as a letter of the alphabet from D through Z, with D 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 has no internal or external flaws |
| IF | Internally Flawless; no flaws inside the stone, minor surface blemishes |
| VVS1, VVS2 | Very, Very Small inclusions |
| VS1, VS2 | Very Small inclusions |
| SI1, SI2 | Small Inclusions |
| I1 | Inclusions are easy to locate and may be visible to the naked eye |
| I2 | Inclusions are obvious and are visible to the naked eye |
| I3 | Inclusions are very obvious |
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 certificate by examining it under a 10-power loupe.
Not all laboratories grade a diamond’s cut. The GIA, 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, like the AGS, 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.
H
HRD
The Hoge Raad vor Diamont is a prestigious independent European gemological certification laboratory based in Antwerp, Belgium that began grading diamonds and providing rading reports in 1976. The HRD does not sell diamonds, but acts as a consultant in the grading of precious gems.
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.
I
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 57 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.
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 blemish that occurs naturally inside or on the surface of diamonds. The fewer inclusions, the more rare the diamond and the greater its value. 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, pave setting, cluster setting and tension setting.
L
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.
M
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.
P
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 | = | .09 - .11 |
| 1/8 | = | .12 - .13 |
| 1/7 | = | .14 - .15 |
| 1/6 | = | .16 - .17 |
| 1/5 |