A diamond's clarity refers to its relative freedom from imperfections – internal inclusions and / or surface blemishes. Flawless diamonds are absolutely clear; they are the most sought after and consequentially, the most expensive.
However, few things in nature are absolutely perfect, and diamonds are no exception. Most diamonds have internal features, called inclusions, and surface irregularities, called blemishes. Together, they are the diamond's 'clarity characteristics'.
Clarity is the relative absence of these clarity characteristics.
Blemishes are surface imperfections including scratches and nicks. Inclusions are internal, though some might break the surface. Tiny diamond or other mineral crystals may be trapped within the diamond as it forms. Depending on their size and location, they may still be there after the diamond has been cut and polished.
How is clarity graded?
Similar to the color scale, a system for grading clarity has evolved that is generally accepted in the industry. Here's how the GIA clarity grading scale works:
Shows no inclusions or blemishes of any sort under 10x magnification when observed by an experienced grader.
IF Internally Flawless
Has no inclusions when examined by an experienced grader using 10x magnification, but will still have some minor blemishes.
VVS1 and VVS2 Very Very Slightly Included
Contains minute minutes that are difficult even for experienced graders to see under 10x magnification.
VS1 and VS2 Very Slightly Included
Contains minute examples such as small crystals, clouds or feathers, when observed with effort under 10x magnification.
SI1 and SI2 Slightly Included
Contains inclusions (clouds, included crystals, knots, cavities, and feathers) that are noticeable to an experienced grader under 10x magnification.
I1, I2, I3 Included
Contains inclusions (possibly large feathers or large included crystals) that are obvious under 10x magnification and may affect transparency and brilliance.
* Within the SI clarity grade, – SI3 – to denote inclusions that are visible to the naked eye, but do not effect transparency and brilliance to a significant degree.
Clarity and Value
Similar to color, carat weight and cut, clarity of influence on value is directly related to rarity. The better the clarity grade, the more desirable and valuable the diamond.