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When you
purchase a diamond there are simple factors that combine to determine
the quality and value of the individual stones you choose.
The important
things to consider are “The Four C’s”. These are :
When you know
what these terms mean you will feel more comfortable about making
your choice.
Certificated
diamonds are a commodity whose characteristics are precisely defined
to agreed international standards, and if you are looking at
certificated stones the above qualities will be listed on the certificate.
Certificates
are issued by testing laboratories and the internationally recognised
establishments that you are likely to encounter are the G I A (the
Gemmological Institute of America) and the H R D. (Hoge Raad voor
Diamant, or The Diamond High Council of Antwerp.) In England the
AnchorCert Gemmological Office is an increasingly accepted
certificating laboratory, attached to the Birmingham Assay Office.
Going back to
the Four C’s : although clarity, color and cut are equally
important the first thing you will probably discuss about your
diamond will be its weight. This will be expressed in carats or
fractions of a carat.
Carat
So what is a
carat ?
From ancient
times the word has been used as a term of weight for gold and
precious stones and it is thought to originate from the practice of
balancing the object to be weighed against a number of seeds from the
Carob tree, the weight of which is remarkably consistent.
Today a carat
is accepted as 200mg or 1/5 of a gram. A carat is divided into 100
points; thus a 1/4 carat (ct) = 25 points (pts). You will frequently
see carat abbreviated as ct and point as pt.
Color
The color tone
of a diamond is denoted by a letter of the alphabet starting at D,
regarded as colorless, to Z, denoting a strong yellow. Although the
absence of color is regarded as a good thing a very strong color will
make a diamond highly desirable. A blue, green or canary yellow
diamond for instance would be sought after.
In practice you
will have no trouble distinguishing between a D (colorless) and say a
P (very faint yellow), but to tell the difference between H and I,
both near colorless, takes a great deal of expertise.
Diamond colors
Clarity
When your
diamond was formed carbon was subjected to incredibly high
temperatures and pressures deep inside the earth. Ideally the process
would result in a crystal clear diamond, but more often than not the
result was a crystal with small marks inside it. When the rough
crystal is polished these marks become apparent; they show up as
black dots and are known as inclusions. Again there is an
international grading system to establish the degree of clarity of
the stone : the greater the degree of clarity, the more desirable the stone.
There are
eleven grades of clarity, from FL (flawless no inclusions) to I/3
(inclusions visible to the naked eye.)
Cut
The cut of a
stone describes its shape and there are eight basic shapes.
Diamond Cut
Whatever the
shape of your diamond you will find the surface covered with small
flats, which are called facets. The proportions of the basic shape
and the way the facets have been cut on its surface are extremely
important to the amount of “life and fire” that the stone exhibits.
Why are these
so important ? We will use the round / brilliant cut diamond as an example.
On the top of
the diamond (the crown) there are 33 facets and on the underside (the
pavilion) there are 25 facets If the proportions of the stone are
correct then you have the ideal “make”.
As light passes
through the crown of the diamond its path is bent and it is reflected
from one facet to another inside the diamond, then reflected back
through the crown to the viewer, giving it its “sparkle”.
At the same time the optical properties of the stone break up the
light into the colors of the spectrum, creating the “fire”.
To make the most of the diamond's natural properties the angles have
to be exactly right; too steep or too shallow and light will escape
through the pavilion. The same principles apply to all the cuts, but
some are more successful at exploiting the diamond's natural
properties than others.
There is one
other property worthy of mention that you will see on a diamond
certificate, which is fluorescence . This is caused by trace elements
of boron found in the diamond and is activated by ultra violet light.
You will find it on the certificate rated as :
None, Faint,
Medium, Medium blue, Strong blue, or Intense blue.
Other colors do
occur (yellow,brown,green,black) but the most commonly seen is blue. |
