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Diamond
4C's of Diamond: CARAT, CLARITY, COLOUR, CUT
Carat (Cts.)
The carat weight measures the mass of a diamond. One carat is defined as
exactly 200 milligrams (about 0.007 ounce). The point unit—equal to one
one-hundredth of a carat (0.01 carat, or 2 mg)—is commonly used for
diamonds of less than one carat. All else being equal, the value of a
diamond increases exponentially in relation to carat weight, since larger
diamonds are both rarer and more desirable for use as gemstones. A
review of comparable diamonds available for purchase in September
2005 demonstrates this effect (approximate prices for round cut, G color,
VS2 diamonds with "1A" cut grade, as listed on http://www.pricescope.
com):
Carat size Cost per carat (US$) Total cost (US$)
0.5 carat (50 points) 3,000 - 1,500
1.0 carat 6,500 - 7,500
1.5 carats 8,500 - 12,750
2.0 carats 13,000 - 26,000
3.0 carats 17,000 - 51,000
5.0 carats 23,000 - 115,000
The price per carat does not increase smoothly with increasing size.
Instead, there are sharp jumps around milestone carat weights, as demand
is much higher for diamonds weighing just more than a milestone than for
those weighing just less. As an example, a 0.95 carat diamond may have a
significantly lower price per carat than a comparable 1.05 carat diamond,
because of differences in demand.
A weekly price list published by Rapaport of New York, of diamond
prices per carat, for different diamond cuts, clarity and weights, is
currently considered the de-facto retail price baseline. Jewelers often trade
diamonds at negotiated discounts off the Rapaport price (e.g., "R -3%").
In the wholesale trade of gem diamonds, carat is often used in
denominating lots of diamonds for sale. For example, a buyer may place
an order for 100 carats of 0.5 carat, D–F, VS2-SI1, excellent cut
diamonds, indicating he wishes to purchase 200 diamonds (100 carats
total mass) of those approximate characteristics. Because of this, diamond
prices (particularly among wholesalers and other industry professionals)
are often quoted per carat, rather than per stone.
Total carat weight (t.c.w.) is a phrase used to describe the total mass of
diamonds or other gemstone in a piece of jewelry, when more than one
gemstone is used. Diamond solitaire earrings, for example, are usually
quoted in t.c.w. when placed for sale, indicating the mass of the diamonds
in both earrings and not each individual diamond. T.c.w. is also widely
used for diamond necklaces, bracelets and other similar jewelry pieces.
Clarity
Clarity is a measure of internal defects of a diamond called inclusions.
Inclusions may be crystals of a foreign material or another diamond
crystal, or structural imperfections such as tiny cracks that can appear
whitish or cloudy. The number, size, color, relative location, orientation,
and visibility of inclusions can all affect the relative clarity of a diamond.
The Gemological Institute of America (GIA) and others have developed
systems to grade clarity, which are generally based on those inclusions
which are visible to a trained professional when a diamond is viewed from
above, under 10x magnification.
Diamonds become increasingly rare when considering higher clarity
gradings. Only about 20 percent of all diamonds mined have a clarity
rating high enough for the diamond to be considered appropriate for use
as a gemstone; the other 80 percent are relegated to industrial use. Of that
top 20 percent, a significant portion contains a visible inclusion or
inclusions. Those that do not have a visible inclusion are known as "eye-
clean" and are preferred by most buyers, although visible inclusions can
sometimes be hidden under the setting in a piece of jewelry.
Most inclusions present in gem-quality diamonds do not affect the
diamonds' performance or structural integrity. However, large clouds can
affect a diamond's ability to transmit and scatter light. Large cracks close
to or breaking the surface may reduce a diamond's resistance to fracture.
Diamonds are graded by the major societies on a scale ranging from
Flawless to Imperfect. (see the main article for more detail)
Colour
A chemically pure and structurally perfect diamond is perfectly transparent
with no hue, or color. However, in reality almost no gem-sized natural
diamonds are absolutely perfect. The color of a diamond may be affected
by chemical impurities and/or structural defects in the crystal lattice.
Depending on the hue and intensity of a diamond's coloration, a diamond's
color can either detract from or enhance its value. For example, most
white diamonds are discounted in price as more yellow hue is detectable,
while intense pink or blue diamonds (such as the Hope Diamond) can be
dramatically more valuable.
Most diamonds used as gemstones are basically transparent with little tint,
or white diamonds. The most common impurity, nitrogen, replaces a small
proportion of carbon atoms in a diamond's structure and causes a
yellowish to brownish tint. This effect is present in almost all white
diamonds; in only the rarest diamonds is the coloration due to this effect
undetectable. The GIA has developed a rating system for color in white
diamonds, from "D" to "Z" (with D being "colorless" and Z having a bright
yellow coloration), which has been widely adopted in the industry and is
universally recognized, superseding several older systems once used in
different countries. The system uses a benchmark set of either natural
diamonds of known color grade, or precision-crafted cubic zirconia; test
lighting conditions are also standardized and carefully controlled.
Diamonds with higher color grades are rarer, in higher demand, and
therefore more expensive, than lower color grades. Oddly enough,
diamonds graded Z are also rare, and the bright yellow color is also highly
valued. Diamonds graded D-F are considered "colorless", G-J are
considered "near-colorless", K-M are "slightly colored". N-Y are usually
appear light yellow or brown.
In contrast to yellow or brown hues, diamonds of other colors are much
rarer and more valuable. While even a pale pink or blue hue may increase
the value of a diamond, more intense coloration is usually considered more
desirable and commands the highest prices. A variety of impurities and
structural imperfections cause different colors in diamonds, including
yellow, pink, blue, red, green, brown, and other hues. Diamonds with
unusual or intense coloration are sometimes labeled "fancy" by the
diamond industry. Intense yellow coloration is considered one of the fancy
colors, and is separate from the color grades of white diamonds.
Gemologists have developed rating systems for fancy colored diamonds,
but they are not in common use because of the relative rarity of colored
diamonds.
Cut
Diamond cutting is the art and science of creating a gem-quality diamond
out of mined rough. The cut of a diamond describes the manner in which a
diamond has been shaped and polished from its beginning form as a rough
stone to its final gem proportions. The cut of a diamond describes the
quality of workmanship and the angles to which a diamond is cut. Often
diamond cut is confused with "shape."
There are mathematical guidelines for the angles and length ratios at which
the diamond is supposed to cut at in order to reflect the maximum amount
of light. Round brilliant diamonds, the most common, are guided by these
specific guidelines, though fancy cut stones are not able to be as accurately
guided by mathematical specifics.
The techniques for cutting diamonds have been developed over hundreds
of years, with perhaps the greatest achievements made in 1919 by
mathematician and gem enthusiast Marcel Tolkowsky. He developed the
round brilliant cut by calculating the ideal shape to return and scatter light
when a diamond is viewed from above. The modern round brilliant has 57
facets (polished faces), counting 33 on the crown (the top half), and 24 on
the pavilion (the lower half). The girdle is the thin middle part. The function
of the crown is to diffuse light into various colors and the pavilion's
function to reflect light back through the top of the diamond.
Tolkowsky defines the ideal dimensions to have:
Table percentage (table diameter divided by overall diameter) = 53%
Depth percentage (Overall depth divided by the overall diameter) = 59.3%
Pavilion Angle (Angle between the girdle and the pavilion) = 40.75°
Crown Angle (Angle between the girdle and the crown) = 34.5°
Pavilion Depth (Depth of pavilion divided by overall diameter) = 43.1%
Crown Depth (Depth of crown divided by crown diameter) = 16.2%
The culet is the tiny point or facet at the bottom of the diamond. This
should be a negligible diameter, otherwise light leaks out of the bottom.
Tolkowsky's ideal dimensions did not include a girdle. However, a thin
girdle is required in reality in order to prevent the diamond from easily
chipping in the setting. A normal girdle should be about 1%–2% of the
overall diameter.
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