GIL’s 4 C’s
The four Cs are the famous four main criteria by which a diamond’s worth is determined.
Most anybody who has ever had any interest in diamonds knows about the four C’s, namely Color, Clarity, Cut and Carat, but not everyone understands what each one reflects nor the grading system used to describe how well a diamond fares in each of the Cs.

Since any and all types of diamond certificates include details regarding the 4Cs it is essential for anyone with any interest in diamonds to learn at least a little about them in order to be able to understand a diamond’s relative qualities and how it’s bottom line worth is assessed.
For your convenience, here are the basics:

Color

A perfect diamond is colorless and graded “D”, on a D through Z scale. Such stones are rare and most diamonds possess some degree of a yellowish brown tint. The more noticeable the tint the greater the impact on a diamond’s worth. But there are exceptions to this rule, if a diamond has a more attractively colored tint, such as red, purple or blue, it may be considered a “fancy colored” diamond and thus become more valuable.

Clarity

Diamonds may have inclusions which interfere with the way light passes through them. Such inclusions may be traces of other minerals trapped within the diamond, tiny fractures or voids. A flawless diamond is one with no inclusions which can be spotted by an expert gemologist studying it in ideal conditions while using X10 magnification. For clarity grades the letters V,S and I are used. A diamond graded VVSI1 for clarity has one Very Very Small Inclusion, a diamond graded VSI2 has two very small inclusions, in a diamond graded SI2 there are two small inclusions, etc. Inclusions graded “I” are visible to the naked eye.

Cut

It is important not to mix cut with shape.
Diamonds may be cut in various different shapes (such as round, oval, marquise, pear, princess, emerald, cushion and others). Whatever shape a diamond is cut in there are ideal proportions which, if achieved, cause light to be reflected in the best manner possible. Expert knowledge is required in order to assess how well a diamond is cut. In a well cut diamond light hitting the stone from above will travel through it, be reflected around in it only to be directed right back out from its top, in this manner the sought after sparkle effect is created.

Carat

Perhaps the most straight forward of the four Cs, a diamond’s carat simply indicated how much it weighs. One carat is 200 milligrams (one fifth of a gram). Since big diamonds are much rarer than small ones the larger the diamond the more it’s per carat cost will be.