Clarity refers to the degree to which these imperfections are present. Diamonds which contain numerous or significant inclusions or blemishes have less brilliance because the flaws interfere with the path of light through the diamond.
Almost all diamonds are graded for clarity using the 11 point diamond clarity scale created by the GIA, including diamonds which were not actually graded by GIA. In grading diamond clarity, the GIA considers the number, size, color, reflectivity, and position of every flaw visible under 10x magnification.
The highest rated stone is a Flawless stone in which it has no inclusions or blemishes are visible to a skilled grader using 10x magnification.