When purchasing a diamond it's important to take into consideration the "4 C's" to help understand pricing, categorization, and evaluation. These are Cut, Clarity, Color, and Carat.

Diamond Cut

This is the most important of the 4 C’s, a well cut diamond displays maximum brilliance, fire and scintillation, which is determined by the proportions, symmetry and polish of the diamond. This is achieved through what is known as planned light leakage. This is based on the proportions of the diamond, in relation to the angles to the crown and pavilion of the diamond.

Symmetry is the alignment and intersecting of the facets. 

Polish is the placement of the facets and the all around finish of the diamond. 

With unplanned light leakage a diamond can result in being too deep or too shallow.

Cut also refers to the shape of the diamonds, Brilliant, Cushion, Oval, Pear, Marquise and Heart are featured with triangular and kite shaped facets for maximum brilliance. Emerald and Asscher cuts are step cut, with concentric rows which run parallel like steps. Mixed cuts are a combination of brilliant and step cut facets.


Clarity

Is the purity of the diamond, graded with 10-power magnification to determine inclusions or identifying characteristics by assessing size, nature, number, color, location and relief within the diamond.

Diamond Clarity Chart

 FL

Flawless (no inclusions are visible under 10-power)

IF Internally Flawless (no inclusions under 10-power, minor blemishes contained to the girdle)
VVS1-2 Very Very Slightly Included (minute inclusions)
VS1-2 Very Slightly Included (minor inclusions)
SI1-2 Slightly Included (noticeable inclusions)
I1-2-3 Imperfect (obvious inclusions)

Color

The cause of color is selective absorption, the ability of a transparent substance (diamond) to absorb some wave lengths of light, while transmitting other wave lengths of light. This is determined by the trace elements in nature such as Nitrogen, which gives a diamond various tints of yellow or the absence of Nitrogen, making a diamond colorless. Where Boron makes a diamond blue and natural radiation makes a diamond green. It is believed that pink and red shades are due to distortion in the crystal structure of the diamond.

Diamond Color Chart

D-E-F Colorless
G-H-I-J Near Colorless
K-L-M Faint yellow
N-O-P-Q-R Very Light Yellow
S-T-U-V-W-X-Y-Z Light Yellow

Carat Weight

Carat weight measures the weight of the diamond, not the size. Different shapes may weigh the same in carat weight but appear larger or smaller visually. The metric carat, which equals 0.200 gram, is the standard unit of weight for diamond.