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Diamond
Ancient civilizations were fascinated by the
exceptional hardness of diamond, although colored gems were
regarded as more aesthetically pleasing. Diamond was extremely
rare up to the eighteenth century and was only fully appreciated
after the modern type of brilliant cut, which shows it in
all its glory, was developed at the beginning of the twentieth
century. It is the most important gemstone today. Statistics
a few years ago showed that diamonds accounted for eighty
percent of the movement of money generated by gemstones. About
two million carats of cut diamonds are issued on the market
each year (it is the only gemstone for which reliable statistics
are available), equal to a volume of little more than 110
liters.
Appearance In most cases it is almost colorless
or, to be more precise, ranges from perfectly colorless (infrequent)
to yellow-tinged or, sometimes, brownish. Diamonds with a
definite color are extremely rare. This can be yellow, yellow-brown,
or predominantly brown or, very occasionally pink to reddish,
blue, blue-gray, pale green, or violet. Its luster, depending
on reflection from both the inner and outer surfaces of the
light incident on the table and crown, is greater than that
of other gemstones, due both to its high refractive index,
which facilitates total internal reflection and its exceptional
hardness, enabling it to acquire a similar degree of polish.
By far the most widely used cut is the round,
brilliant type, which best displays the gem's unique characteristics.
But oval, marquise, pear and, more rarely, heart-shaped fancy
cuts are also used. Most of these have a girdle consisting
of a series of small, polished facets, while in brilliants,
a girdle cut this way is uncommon and is reserved for stones
treated with particular care. The special, rather elongated
forms often show a dull area along the minor axis. Obviously,
the better the cut, the less this band will show. The so-called
emerald cut is also quite common.
This has a rectangular table, stepped and chamfered.
Unfortunately, this cut, which is used to reduce wastage when
the stone is fashioned, is more often than not given the wrong
proportions. The crown is usually too shallow (even less than
10 percent of the smaller side of the girdle) and the pavilion
too deep (50-55 percent of the smaller side). The result is
a stone with a lot less fire than one with a brilliant cut,
or even than the rare examples of gems with correctly proportioned
emerald cuts.
Diamonds are also found on the market with unusual,
antique or specially designed cuts. Old mine cuts are not
normally circular, but squarish, with rounded corners, or
almost rectangular with rounded corners (some people call
in South Africa these polygonal shapes with slightly curved
sides and smoothed corners “cushion" shape).
The proportions of the height of the crown,
the pavilion and the diameter vary a great deal in these cases,
depending on the creativity of the cutter. It is still possible
to find what are known as “rose” cuts, with a
flat base, both in stones of some size, which are usually
old or antique, and in small, shallow stones one or two millimeters
in diameter, generally used in old-fashioned jewelry.ss
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