The 4 C's
Before the Gemological Institute of America (GIA) established the ‘4 C’s’, there was no official grading system in place. GIA developed a grading system that could uses to accurately describe and grade Diamond quality without inconsistency or misinterpretation.
Most people consider Carat to be a size, but Carat is actually a weight of measurement. A 1.00 carat Diamond is equal to 1/5 of a gram. If all other factors are equal, the Diamond prices increase with the Carat Weight.
Clarity of a Diamond refers to the amount of, or lack of imperfections in the Diamond crystal. Clarity Grades are based on the size, nature, color, number and relief of inclusions or imperfections in the stone or on the surface that can be seen under 10x magnification.
The Color Grade of a Diamond refers to how closely the approach colorlessness. The grading scale for Color is alphabetic from D-Z. D color grade represents colorless (no signs of color) down to a Z color grade where the Diamond will appear more brown or yellow in hue.
Cut first refers to shape, or the outline of the stone. Popular cuts or shapes for Diamonds include Round Brilliant, Asscher, Radiant, Cushion, Princess, Pear, Oval, Heart, Marquise, Emerald etc.
The second part of cut refers to the Cut Grade attached to Round Brilliant cut stones. Cut refers to the proportions and angles of a Round Brilliant Diamond and their relation to the brilliance and sparkle. Cut Grades are assessed by Brightness, Fire, Scintillation, Weight Ratio, Girdle Thickness, Symmetry and Polish. Cut Grade is assigned From Excellent to Poor.