quality and value of diamonds are measured by four characteristics
known as the 4C's. The 4C's relate to a diamond's cut, colour, clarity
and carat weight. The quality of a diamond is measured by its cut,
colour and clarity. The carat weight measures the size of the diamond.
Of all the 4C's, cut is the characteristic directly influenced by
man; colour, clarity and carat weight are all dictated by nature.
A diamond in its natural, uncut state
is described as a "rough diamond". Its
natural appearance so resembles a glass
pebble that most people would pass it
by without a second glance. It is the
skill of the diamond cutter that unlocks
the brilliance for which diamonds are
two identical diamonds are placed side by side and one is less brilliant
and fiery than the other, the fault lies in the cutting. Such a
stone cannot demand as high a price as a well-cut diamond.
is important to distinguish between cut and shape. Some of the more
popular shapes of diamonds include Round Brilliant, Oval, Marquise,
Pear, Heart and Emerald. Within each of these shapes, however, it
is the cut that determines the quality of the stone. For example,
most diamonds are cut with 58 facets, regardless of their shape.
A diamond's colour is one of the most important factors
in determining its value. The nearer a white diamond is to being
absolutely colourless, the more rare and valuable it is. The graduations
in colour are so subtle that intricate international grading scales
have been devised.
are graded into categories defined by letters. The colour range
from exceptional whites (categories D, E and F) to tinted colours
(categories M to Z). The best way to pinpoint a diamond's true colour
is to place it next to another diamond that has previously been
are also fancy coloured diamonds and these are graded according
to their intensity of colour, not lack of it. There are a variety
of reasons for diamonds to be coloured. The most common causes,
or suggested causes, for the colours yellow, green, blue, brown
and pink are described below.
When nitrogen combines with the diamond crystals during the formation
stage it causes a surplus electron in the bonding. This surplus
electron absorbs blue light, thus giving off a yellow colour.
Yellow diamonds also occur when aggregates of three nitrogens
combine and cause surplus bond.
The elements of boron may also be substituted within a diamond
during its formation. Boron absorbs red light, hence in the absence
of nitrogen, diamonds containing boron are blue in colour. An
example of a diamond containing boron is the famous Blue Hope
diamond. Diamonds containing boron also exhibit unusual electrical
properties and are semi-conductive in nature. Hydrogen is another
impurity that, in high quantities, can cause grey or blue colouring
in diamonds. However, these diamonds are not semi-conducting.
vacancy in the regular lattice of atoms within a diamond results
in a green colouring. Carbon atoms being knocked out of their
regular position by other particles cause vacancies. The depth
of colour usually extends about 2mm below the diamond's surface.
At extremely high temperatures the vacancies can become mobile
and can combine with nitrogen to form other colours such as mauve,
orange, blue or gold.
has been suggested that dislocations in the regular lattice of
atoms, caused by severe forces deep in the earth, may be responsible
for the brown colouring of champagne and cognac diamonds. The
dislocated bonds may affect the light wavelength, thus producing
a diamond which is coloured, but which contains no impurities.
has also been suggested that combinations of dislocations, vacancies,
and non-nitrogen impurities cause the much sought-after colouration
in pink diamonds. However these theories are still being developed.
During the formation of a diamond it is possible for minute particles
of non-crystallised carbon or non-diamond crystals to be caught
within the diamond. These imperfections are called inclusions and
provide each individual diamond with unique characteristics.
may not always be visible to the naked eye, however they do interfere
with the passage of light through the diamond. Therefore the fewer
inclusions a diamond has, the more valuable it is.
colour, clarity is also categorised using international grading
scales. The categories of clarity are based upon the number, size
and position of the inclusions within the diamond. Gradings range
from flawless, and internally flawless, through very small and small
inclusions, to imperfect. The clarity gradings are described as
internal or external blemishes when examined under a 10x microscope.Diamonds
in this category cannot contain internal graining that is
reflective whitish, coloured,or which significantly affects
internal inclusions but minor surface blemishes which cannot
be removed with polishing. That is, characteristics such as
surface grain lines, natural and extra facets on the crown.
Blemishes that can be removed by minor repolishing separate
the internally flawless from the flawless grade.
Very Slightly Included
inclusions, such as reflective internal graining, difficultto
locate using a 10x microscope
inclusions, such as small included crystals which are visible
using a 10x microscope.
that can be seen easily under a 10x microscope,and may also
be seen with the naked eye using a white background. Inclusions
in these diamonds cannot be seen through the crown of the diamond.
can be seen with the naked eye, and are quite obvious under
a 10x microscope.
can be seen with the naked eye, and may interfere with transparency
Dark inclusions which are very noticeable to the naked eye,
and which interfere with transparency. Diamonds in this category
may contain cleavages that are likely to become worse with
A carat is the unit of measure used to determine the weight of
a diamond. The term "carat" is derived from the original method
of using carob tree seeds to weigh diamonds. One seed from this
tree was equivalent to one carat.
actual weight of one carat is now established at 0.2 grams. To assist
in accurately describing the weight of diamonds each carat is divided
into 100 points. Diamonds of less than one carat in weight are known
as "pointers". For example, a 0.15 carat diamond would be called
a "15 pointer".
are usually weighed prior to setting for more accurate measurements.
Diamonds are priced per carat, according to their size and quality.
Although the carat weight of a diamond is indicative of its size,
it is not necessarily indicative of a diamond's quality. Therefore,
where two diamonds have the same carat weight, the one of better
quality will command a higher price per carat.