EGL Asia Diamond Grading Lexicon Glossary
By
Paul Glen,
paul [at] relevantsitecontent . com
http://www.eglasia.com.hk/diamondLexicon.html
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CARAT
“Carat” is one of the four Cs according to which a diamond
is graded, and one of the components that help a diamond buyer
to determine the quality of the gemstone he or she is about
to purchase. It also is the easiest to understand and measure,
inasmuch as it refers to weight. Furthermore, because the
density of diamonds is essentially constant, as the caratage
of the diamond increases, so does its relative size. The term
“carat” is the measurement used to designate the weight of
gemstones, including diamonds. It originates from the Greek
word "karaton," which was the carob seed that was
used to balance scales in ancient times. A carat is equal
to 200 milligrams. Carats are subdivided into points and there
are 100 points in one carat.
CLARITY
Clarity is one of the four Cs according to which a diamond
is graded, and one of the components that help a diamond buyer
to determine the quality of the gemstone he or she is about
to purchase. It essentially refers to the purity of the diamonds,
or to the degree to which it is free of blemishes and imperfections.
On principal, as the clarity of the diamond is improved, its
value is enhanced. The clarity of a polished diamond is affected
by both external blemishes and internal imperfections or inclusions,
which were created in nature when the diamond was formed.
Internal inclusions include piqués, or dark spots, gas bubbles
or lines, and even tiny crystals. Clouds are clumps of microscopic
inclusions that lower the transparency of the diamond crystal.
Sometimes cracks in the diamond crystal, or fractures or feathers
affect clarity, passing through the interior and sometimes
reaching the surface. Most occurred during the crystallization
of the gemstone, but on occasion they resulted during the
cutting and polishing process, or some cane about as a result
of wear and tear after being worn in jewelry.
COLOR
Color is one of the four Cs according to which a diamond is
graded, and one of the components that help a diamond buyer
to determine the quality of the gemstone he or she is about
to purchase. To first-time diamond buyers, it often comes
as a surprise that diamonds come in a wide range of colors,
ranging from colorless to yellow, but even blue, green, orange
and sometimes red. Nonetheless, the majority of diamonds fall
within a color range that runs from colorless (sometimes called
white) to near- colorless and then to lightly yellowish or
brownish. Color is evaluated by gemologists who compare stones
to a standard master set. Today there are electronic systems
which can assign grades, but members of the trade still consider
a human evaluation to be more accurate. The slight variations
that occur in a diamond’s color form the basis of a generally
accepted color grading system that uses the letters of the
alphabet, in which D is the highest grade, and it is assigned
to a completely colorless or white diamond – a rare phenomenon.
Near-colorless diamond are graded with the letters E and F.
The most common color grades encountered by diamond consumers
run from the color grade G through the color grade M. Diamonds
that display a slight yellowish or brownish hue receive the
color grades K, L or M. The color grades N, O, P, Q and R
represent stones with a progressively light yellowish tint,
while the grades S down to Z represent diamond that show an
increasingly yellowish or brownish hue. When diamonds are
of a truly vivid color, for instance a lively “canary” yellow
or a distinctive pink, they are defined as fancy colored diamonds.
Here, the alphabetical color scale does not apply and they
generally are described according to their hue, and the intensity
of the color. Fancy colored stones are valued very highly—even
more so than colorless diamonds.
CROWN
The section of a diamond above the girdle plane
CUT
Cut is one of the four Cs according to which a diamond is
graded, and one of the components that help a diamond buyer
to determine the quality of the gemstone he or she is about
to purchase. The shape of the diamond is also sometimes referred
to as the cut. In such instances, the term “cut” is not a
criterion for placing a value on a diamond. The quality of
the cut, or the “make,” as diamond dealers often say, is crucial.
It is this that decides how the light entering the stone will
react, and consequently how brilliant the stone will appear.
A poorly cut diamond will actually loose light and appear
dull. In the modern age, diamond cutters do their utmost to
fashion each stone according to an exact mathematical formula,
in order to achieve a finished product that is most pleasing
to the eye. The most famous formula for a round brilliant
stone was introduced in 1919 by a Belgian mathematician, Marcel
Tolkowsky. Experts agree that cut is one of the most difficult
qualities to judge. Currently most gem labs assign descriptions
of “poor,” “fair,” “good” or “excellent” in their diamond
grading reports.
FLAWLESS, INTERNALLY FLAWLESS (FL, IF)
This is the grade given to a polished diamond where no external
blemishes or internal inclusions are visible using a standard
10X-magnification loupe. Experienced jewelers seldom see such
stones, and some even argue that flawless diamonds simply
do not exist.
FLUORESCENCE
Fluorescence is the effect viewed when a diamond glows under
ultra-violet light (UV). Some 50 percent of polished diamonds
display fluorescence, most of them in a blue hue, but sometimes
other colors, especially yellow, can be observed. When diamond
displays relatively strong fluorescence, it can cause a diamond
to look somewhat “hazy” and therefore, less transparent.
HEARTS & ARROWS
‘Hearts & Arrows’ diamonds are precisely cut round brilliants
that, when examined using a special viewer, display eight
hearts though the pavilion from below and eight arrows through
the crown from above. As top-quality cut stones, they typically
fetch a premium in the market.
INCLUSION ( I1, I2, I3)
With I1 the best of the three, followed by I2 and I3, these
grades are assigned to diamonds where the inclusions can be
seen easily with the naked eye.
LIGHT PERFORMANCE
In an ideally-proportioned diamond, all of the light entering
the diamond from the top will bounce within the diamond and
be reflected back through the top, giving the stone maximum
brilliance and fire. If the stone is too shallow or too deep,
some light will escape through the bottom part of the diamond,
giving the appearance of shadows when viewed from the top.
MEASUREMENT
Measurement is the diameter of the diamond by the depth of
the diamond, expressed in millimetres.
NATURAL DIAMONDS
Natural diamonds are diamonds that have been found in nature,
and have not been subject to unnatural treatments that may
affect their appearance, such as High Pressure, High Temperature
(HPHT) treatments and irradiation, which could affect color,
and fracture filling and drilling which could affect clarity.
In and of themselves, these treatments are not illegal, but
they should be disclosed to the buyer before a transaction
is completed, because they may have a bearing on price. Diamonds
that are created in the laboratory or factory are alternatively
known as synthetic, man-made, laboratory grown or factory
grown.
PAVILION
The section of the polished gemstone below the girdle. The
pavilion depth percentage is the distance from the girdle
plane to the culet, expressed as a percentage of the girdle
diameter of round diamonds or as a percentage of the width
of the polished stone in a fancy shaped diamond.
POLISH
The overall quality of the work done in producing a polished
stone. Polish influences how well light is able to pass through
a diamond and is very important to a diamond's brilliance.
PROPORTION
Essentially “proportion” refers to the polished stone’s proportions,
or the size of each of its various facets—flat, polished planes—and
the angles at which they lie relative to each other.
SHAPE
Shape refers to the way that the stone is cut. Common shapes
are round, marquise, oval, pear-shaped, heart-shaped, princess
(square), and radiant (also square).
SLIGHTLY INCLUDED (SI1, SI2, SI3)
With SI1 being the better of the three, these diamond's inclusions
can be detected with difficulty with the naked eye, but are
quite obvious under the magnification of a 10X loupe. When
of good color and make, such stones are an excellent choice
for an expensive designer jewelry piece.
SYMMETRY
Symmetry refers to the exactness of the shape and arrangement
of facets. This includes naturals, misshapen facets and extra
facets, off center culets and tables, wavy and out of round
girdles, misalignment of crown and pavilion facets
TABLE
The table is the large, central plane or facet on the crown
of a polished diamond, through which most of the light enters
the stone, and out of which most of it is reflected. The relative
size of the table is different for every cut.
TYPE
Diamonds can be scientifically classified into 4 types, known
as type 1a, 1b, 2a, and 2b. Diamonds are made of carbon, and
are extremely pure, but in almost all diamonds there are tiny
proportions of other elements, interspersed within the carbon
as part of their crystal structure. Type 1 diamonds contain
nitrogen. If the nitrogen atoms are clustered together within
the carbon lattice, then the diamond is said to be a Type
1a diamond. About 98% of all diamonds are type 1a. Because
these diamonds absorb blue light, they can have a pale yellow
or brown color. In Type 1b diamonds, the nitrogen atoms are
evenly spread out throughout the carbon lattice. These diamonds
absorb green light as well as blue light, and have a darker
color than type 1a diamonds. Depending on the precise concentration
and spread of the nitrogen atoms, these diamonds can appear
deep yellow ("canary"), orange, brown or greenish.
Less then 0.1% of diamonds belong to Type 1b. Type 2a diamonds
contain no, or minuscule amounts of non-carbon elements and
are usually colorless. However, an imperfect carbon lattice
will make the diamond absorb some light, which will give it
a yellow, brown or even pink or red color. 1-2% of diamonds
belong to Type 2a. Type 2b contain no nitrogen, but they do
contain boron, which absorbs red, orange and yellow light.
These diamonds therefore usually appear to be blue, although
they can also be grey or nearly colorless. All naturally blue
diamonds belong to Type 2b, which makes up 0.1% of all diamonds
VERY SLIGHTLY INCLUDED (VS1, VS2)
With VS1 being the better of the two, such diamonds appear
clean when seen with the naked eye, but the inclusions are
relatively easily spotted with a 10X loupe. More readily available
in the market, these stones are still in the high-end market
range.
VERY VERY SLIGHTLY INCLUDED (VVS1, VVS2)
With VVS1 being the better of the two, such grades are assigned
to diamonds in which imperfections and inclusions are very
difficult to spot, even under the magnification of a 10X loupe.
Such diamonds are rare and most definitely are high-end market
stones.
Published - July 2009
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