Diamonds are natural, formed over millions of years by heat and pressure. They are composed totally of carbon. As a natural material diamond is not uniform all the way through and there are imperfections. These imperfections can vary a great deal but the imperfections that most effect clarity in cut diamonds are inclusions. This is so because inclusions interfere with, or distort the passage of light through the diamond. This can cause the diamond to appear blurred, or not clear to some degree. A diamond without such flaws is of the highest quality and can be appreciated by the intensity of its brilliance and beauty.

Clarity is defined on the scale illustrated below. Gemologists grade diamonds for clarity just as they do for color. The range of clarity starts from FL (flawless diamond) to I3(imperfect, with inclusions that can be seen with the naked eye).