Clarity, or purity, is the most significant factor in diamond's evaluation. The ideal, 100-percent-clear diamond does not include any admixtures and does not have any defects. Both inner and surface defects can affect the quality of the gem, its look, and its price. With regard to surface defects, some superficial scratches can be removed easily with ordinary polishing and thus not affect the stone’s value. On the other hand, some inner defects, such as cleavages, can significantly reduce the gem's value, unless a carefully chosen setting is used to hide the defects. Usually, clarity of a mineral can be checked with a common 10x magnifying glass.
Diamond clarity is evaluated according to the GIA’s scale recognized worldwide. According to this scale, the letter F stands for flawless, ideally pure diamonds without any cleavages, feathers, or inclusions. Defects visible with a magnifying glass at a certain angle are labeled with: IF (for internally flawless diamonds), VVS1 (very, very small inclusions) and VVS2. Stones labeled as VS1 (very small inclusions), VS2, and SI1 (small inclusions), or SI2 possess certain defects which significantly reduce the diamond’s value. Stones labeled as “imperfect” (e.g. I1, I2, or I3) are the least valued as they have inclusions and defects visible to the naked eye; such inclusions damage the aesthetic properties, longevity, and durability of a stone.
In Russia, a slightly different defect-evaluation system is used called the numeric system. The numeric system assigns values starting from 1, which is absolutely flawless and clear. The greater is the number, the more significant are the defects or inclusions. Two separate scales are used for diamonds depending on their size: the 1 to 9 scale is used for diamonds weighing less than 0.29 carat, and the 1 to 12 scale is for larger gems.