Caratage
This refers to the weight of the stone. The name is derived
from the seed (kuara) of the African Coral tree or from the
kernel (Greek keration) of the Carob bean. One carat=1/5gram
(200 mg or 0.2 gram). One carat=100 points. So a diamond of
50 points = 1/2 carat or 0.50ct (and 100mg in weight). One point=1/100
carat or 0.01ct. As a rough guide, a diamond of 1/2 carat has
an approximate diameter of 5mm; a 1 carat of 6.5mm and a 2 carat
of 8mm. If a 1.0ct diamond had a value of £750, a 2.0ct would
not necessarily be worth £1,500 but maybe £3,000 or more. Large
diamonds are rare. The carat weight of gems is not to be confused
with the carat (gold content) used by a goldsmith.
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Colour
Diamonds are graded using a colour scale that ranges from
D (exceptionally white and colourless) to Z (yellow tinted).
Colours D, E, F are recommended for the purist; G, H, I are
near colourless and are recommended for most customers. Colours
J, K, L, M show faint colour and are recommended for the budget
conscious. The rarer strong colours (green, red, blue, purple,
brown, yellow and black), the so-called fancy colours are graded
and valued individually.
Clarity
Most diamonds have imperfections; impurities, non-crystallized
carbon, cracks or scratches, also called inclusions. Most inclusions
can only be seen under magnification. These are labelled in
the following manner:
- Flawless (F) - no inclusions or blemishes seen under × 10
magnification
- Internally Flawless (IF) - no inclusions, with some minor
surface blemishes
- Very, Very Slightly Included (VVS1 and VVS2) - containing
minute inclusions that are difficult to see under X10 magnification
- Very Slightly Included (VS1 and VS2) - inclusions are clearly
seen although minor and small
- Slightly Included (SI1 and SI2) - inclusions are noticeable
and fairly easy to see under the X10 magnification
- Imperfect (I1, I2 and I3) - inclusions that are obvious
under × 10 magnification or can be seen with the unaided eye
Cut
This is the arrangement of the diamonds facets. The facets
are planned and proportioned so that ambient light is reflected
from one facet to another until the light exits from the top
or crown of the diamond. Symmetry refers to how well the facets
line up with each other. It can take from several hours to several
months to cut and polish a diamond, depending on size, shape
and style of the final product. During cutting and polishing,
a rough diamond will lose approximately 50% of its original
weight. The final finish is graded as below;
- Very good -exceptional brilliance.
Few and only minor outer marks. Very good proportions
- Good - good brilliance. Some
outer marks. Proportions with some deviations
- Medium - slightly less brilliance.
Several larger outer marks. Proportions with considerable
deviations
- Poor - brilliance considerably
less. Large and/or numerous outer marks. Proportions with
very distinct deviations
Miscellaneous Information
- If you want to be humorous there is a fifth C - credit card!
- The name diamond refers to its hardness - it is the Greek
adamas
- Its cutting resistance is × 140 harder than that of ruby
or sapphire which is the next hardest stone
- The hardness of diamond is different in the individual
crystal faces - this allows the diamond to be cut.
- Because of the diamond cleavage care must be taken NOT to
accidentally bang against the edge of a diamond - this includes
when setting. Diamonds can and do break.
- Diamond is a simple crystalline structure of carbon produced
by extremely high pressure and temperature.
- They are formed at great depth between 150 - 300km below
the earths surface. By volcanic eruption they came to the
surface or close to it with the rising magma.
- Diamond is generally insensitive to chemical reactions.
- High temperatures can induce etchings on the facet - care
must be taken when soldering near a diamond.
- The melting point of diamond is 4,000 Celsius or about
× 2.5 higher than the melting point of steel
- Important diamond mines are found in the following countries
- Zaire, Botswana, Angola, Ghana,
Central African Republic, Venezuela, Guinea,
Liberia, Russia, Australia (largest producer
of diamonds but not of quality!), China and Canada
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