Truly flawless diamonds are very rare, and very expensive, so you
will seldom face the task of selecting a perfect diamond. It is a fairly
simple matter to find beautiful diamonds with no flaws visible to the
naked eye and buy them at reasonable prices.
Diamonds are graded using a system that judges the stone on its
colour, clarity, cut and carat weight - commonly known as the "Four
C's."
In this section, you will learn what each of the C's means and how it affects the value of the diamond.
'C' for cut

The cut of a diamond refers not only to the shape of the diamond and
number of facets, but also to the quality of the cut. A diamond with
uneven or poorly proportioned facets won't be given the same grade of
cut as an ideally proportioned and masterfully cut stone. This
information will be found on the certificate of a certified diamond.
How a diamond has been cut, polished and to what proportion and
symmetry are of utmost importance since these factors determine the
life, brilliances and dispersion of the diamond. If these factors fall
below standard, the appearance of the diamond will be adversely
affected.
Although most diamonds on the market today are round brilliants,
there are many different shapes available. The following chart shows
some of the most popular shapes:

'C' for clarity

It is very common for diamonds to be formed with slight
imperfections. These are known as "inclusions" and can come in many
forms, including tiny white points, dark dots, or feathery cracks. The
fewer inclusions, the more the stone is worth. A diamond's clarity
ranking is determined by the number, size, type and placement of the
inclusions.
In order to grade the clarity of a diamond, it is necessary to
observe the number and nature of any internal characteristics in the
stone as well as their size and position. This Diamond Clarity Grading
is carried out using the IGI scope and a loupe 10x under the experienced
eye of laboratory gemologists. A diamond is said to be “Internally
Flawless” when it presents no internal defects under 10x magnifications.
'C' for color

Most diamonds appear colorless but actually have slight tones of
yellow or brown. The closer the stone comes to colorless, the more
valuable it is. Diamonds are graded on a color scale ranging from D
(colorless) to Z (heavily tinted.)
'C' for carat


The weight or size of a diamond is measured in carats (ct.). A carat
is 0.2 grams and there are 100 points (or 200 milligrams) per carat. The
Carat measurement of a diamond is actually a measurement of the
Diamond's weight rather than its size or diameter. Do not confuse carat
with karat. Carat refers to stone weight while karat refers to fineness
of gold.