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About the 4Cs
Because diamonds are so valuable, it’s essential to have a universal grading system for comparing their quality. In the 1940s and ’50s, GIA developed the 4Cs and the GIA International Diamond Grading System™ to objectively compare and evaluate diamonds.
Diamonds and other gemstones are weighed in metric
carats: one carat is equal to 0.2 grams, about the same weight as a
paperclip. (Don’t confuse carat with karat, as in “18K gold,” which
refers to gold purity.)
 Just
as a dollar is divided into 100 pennies, a carat is divided into 100
points. For example, a 50-point diamond weighs 0.50 carats. But two
diamonds of equal weight can have very different values depending on the
other members of the Four C’s: clarity, color and cut. The majority of
diamonds used in fine jewelry weigh one carat or less.
Because
even a fraction of a carat can make a considerable difference in cost,
precision is crucial. In the diamond industry, weight is often measured
to the hundred thousandths of a carat, and rounded to a hundredth
of a carat. Diamond weights greater than one carat are expressed
in carats and decimals. (For instance, a 1.08 ct. stone would be
described as “one point oh eight carats,” or “one oh eight.”) The
carat, the standard unit of weight for diamonds and other gemstones,
takes its name from the carob seed. Because these small seeds had a
fairly uniform weight, early gem traders used them as counterweights in
their balance scales. The modern metric carat, equal to 0.2 grams, was
adopted by the United States in 1913 and other countries soon after.
Today, a carat weighs exactly the same in every corner of the world.
Diamond color is all about what you can’t see.
Diamonds are valued by how closely they approach colorlessness – the
less color, the higher their value. (The exception to this is
fancy-color diamonds, such as pinks and blues, which lie outside this
color range.)
 Most diamonds found in jewelry stores run from colorless to near-colorless, with slight hints of yellow or brown.
GIA’s
color-grading scale for diamonds is the industry standard. The scale
begins with the letter D, representing colorless, and continues with
increasing presence of color to the letter Z, or near-colorless. Each
letter grade has a clearly defined range of color appearance. Diamonds
are color-graded by comparing them to stones of known color under
controlled lighting and precise viewing conditions. Many of these
color distinctions are so subtle as to be invisible to the untrained
eye. But these slight differences make a very big difference in diamond
quality and price. Before
GIA developed the D-Z Color Grading Scale, a variety of other systems
were loosely applied. These included letters of the alphabet (A, B and
C, with multiple A’s for the best stones), Arabic (0, 1, 2, 3) and Roman
(I, II, III) numerals, and descriptions such as “gem blue” or “blue
white.” The result of all these grading systems was inconsistency and
inaccuracy. Because the creators of the GIA Color Scale wanted to start
fresh, without any association with earlier systems, they chose to start
with the letter D—a letter grade normally not associated with top
quality.
Because diamonds formed deep within the earth, under
extreme heat and pressure, they often contain unique birthmarks, either
internal (inclusions) or external (blemishes).
Diamond
clarity refers to the absence of these inclusions and blemishes.
Diamonds without these birthmarks are rare, and rarity affects a
diamond’s value. Using the GIA International Diamond Grading System™,
diamonds are assigned a clarity grade that ranges from flawless (FL) to
diamonds with obvious inclusions (I3). Every diamond is
unique. None is absolutely perfect under 10× magnification, though some
come close. Known as Flawless diamonds, these are exceptionally rare.
Most jewelers have never even seen one. The GIA Clarity Scale contains 11 grades, with most diamonds
falling into the VS (very slightly included) or SI (slightly included)
categories. In determining a clarity grade, the GIA system considers the
size, nature, position, color or relief, and quantity of clarity
characteristics visible under 10× magnification. Flawless (FL) - No inclusions or blemishes are visible to a skilled grader using 10× magnification
Internally Flawless (IF) - No inclusions and only blemishes are visible to a skilled grader using 10× magnification
Very, Very Slightly Included (VVS1 and VVS2) - Inclusions are difficult for a skilled grader to see under 10× magnification
Very Slightly Included (VS1 and VS2) - Inclusions are clearly visible under 10× magnification but can be characterized as minor
Slightly Included (SI1 and SI2) - Inclusions are noticeable to a skilled grader using 10× magnification
Included (I1, I2, and I3) - Inclusions are obvious under 10× magnification and may affect transparency and brilliance Like
the color scale, GIA’s clarity grading system developed because
jewelers were using terms that were easily misinterpreted, such as
"loupe clean", or "piqué". Today, even if you buy a diamond in another
part of the world, the jeweler will likely use terms such as VVS1 or
SI2, even if her language is French or Japanese instead of English.
Cut is the factor that fuels a diamond’s fire, sparkle and brilliance.
The traditional 58 facets in a round brilliant diamond, each
precisely cut and defined, are as small as two millimeters in diameter.
But without this precision, a diamond wouldn’t be nearly as beautiful.
The allure of a particular diamond depends more on cut than anything
else. Though extremely difficult to analyze or quantify, the cut
of any diamond has three attributes: brilliance (the total light
reflected from a diamond), fire (the dispersion of light into the colors
of the spectrum), and scintillation (the flashes of light, or sparkle,
when a diamond is moved). An understanding of diamond cut begins
with the shape of a diamond. The standard round brilliant is the shape
used in most diamond jewelry. All others are known as fancy shapes.
Traditional fancy shapes include the marquise, pear, oval and emerald
cuts. Hearts, cushions, triangles and a variety of others are also
gaining popularity in diamond jewelry. As a value factor, though,
cut refers to a diamond’s proportions, symmetry and polish. For example,
look at a side view of the standard round brilliant. The major
components, from top to bottom, are the crown, girdle and pavilion. A
round brilliant cut diamond has 57 or 58 facets, the 58th being a tiny
flat facet at the bottom of the pavilion that’s known as the culet. The
large, flat facet on the top is the table. The proportions of a diamond
refer to the relationships between table size, crown angle and pavilion
depth. A wide range of proportion combinations are possible, and these
ultimately affect the stone’s interaction with light. In early 2005, GIA unveiled a diamond cut grading system
for standard round brilliants in the D-to-Z color range. This system,
the product of more than 15 years of intensive research and testing,
assigns an overall diamond cut grade ranging from Excellent to Poor. The
distance from the bottom of the girdle to the culet is the pavilion
depth. A pavilion depth that’s too shallow or too deep will allow light
to escape through the sides or the bottom of the stone. A well-cut
diamond will direct more light through the crown.
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