The value of loose diamonds is based on the 4 C’s: cut, carat, color and clarity.  “Ideal cut” refers to a specific set of guidelines relative to the highest level of brilliance and fire.  The better the cut, the more dazzling the diamond will be as its ability to take in, refract and project light will be optimized.  Cut is sometimes used to refer to the shape of the diamond, such as round, oval, pear and heart.  A princess cut is a square stone whereas an emerald cut is rectangular. Marquise refers to an elongated oval with points on each end. 

Carat is used to express the weight of loose diamonds.  One carat is 200 milligrams of weight. Carat is the same word used to describe the percentage of gold in the composition of a metal, but is not the same as a carat of weight for diamonds.  Higher carat-weight diamonds are not necessarily higher in value than smaller ones. Different carat weights are considered ideal for different pieces of jewelry and of course depend on individual tastes and budgets.  Certain shapes, particularly pear and marquise, are excellent choices for smaller diamonds as the cut gives the stone a larger appearance. 

The normal color of loose diamonds ranges from colorless which is considered ideal to slightly yellow.  Diamond color is classified or “graded” using the letters D through Z.  D is the most colorless and most valuable, whereas Z has the most color.  Diamonds with a grade of D, E and F are considered colorless and the highest quality of color.  G, H, I and J diamonds are nearly colorless.  N – R diamonds have a very light yellow tint, and the remaining grades, S-Z are light yellow.  The metal in which a diamond is set, such as yellow gold, can affect its color.

A diamond’s clarity is a measure of the ability of light to pass through it unimpeded.  Loose diamonds typically have “inclusions” or small blemishes inside the stone and are part of the unique makeup of each stone. A careful drawing is made of each diamond to indicate where inclusions lie.  However, only those blemishes visible at 10x magnification are considered when assigning the diamond’s clarity rating.  Clarity is graded as F for flawless, IF for internally flawless, VVS1 or VVS2 for very, very slightly included, VS1 and VS2 for very slightly, SI1 and SI2 for slightly and I1, I2 and I3 for inclusions visible to the naked eye.