Of the Four Cs, clarity is the easiest to understand and grade, and leading experts believe that clarity generally bears the least impact on a diamond's appearance. Clarity refers to the naturally occurring inclusions inside the stone, these are also known as the diamond’s “finger prints”. As inclusions tend to be minuscule, they do not in most cases affect the beauty of a diamond in a noticeable way. Inclusions can appear as white spots or black carbon deposits which formed inside the stone during the crystallization process. Other inclusions can occur as tiny cracks, feathers and other internal vein-like characteristics. Diamonds that have the least amount of inclusions will be given the highest clarity grades.
The clarity grading scale begins at the top with Flawless, also known as F. Flawless diamonds possess zero blemishes both on the exterior and interior of the stone. These are the most rare and expensive of the clarity grades.
FL, on the clarity scale, is followed by Internally Flawless, or IF. An internally flawless diamond has no interior inclusions, but may possess one or more exterior imperfections. Internally flawless diamonds are also extremely rare and valuable.
Following IF is VVS, or Very Very Slightly Included. VVS is split into two categories, VVS1 and VVS2, the latter having marginally more inclusions than the first. After VVS is VS, or Very Slightly included. VS also has two sub-grades, VS1 and VS2. VS is followed by SI, or Slightly Included, which has three sub-grades, SI1, SI2 and SI3.
Inclusions in the VVS, VS and SI grades are not visible to the naked eye and can generally only be viewed under intense magnification by a trained professional. Following SI on the clarity scale are I, for included, and C, which are commercial quality diamonds.