Clarity is a measurement of how many blemishes or inclusions are present in the diamond.
The lower the clarity of a diamond, the more imperfections in the diamond.
FROM FLAWLESS TO INCLUDED — FIVE MAJOR GRADES OF CLARITY:
The numbers after the major grade are a sub-grade, with the lower number being better. So a VS1 is superior to a VS2, which is superior to a SI1. Diamond clarity is graded by viewing the diamond through a 10x magnification with a tool called a loupe.
FLAWLESS AND INTERNALLY FLAWLESS (FL, IF)
Both FL and IF diamonds have no internal inclusions visible with magnification. IF diamonds may have very small blemishes present on the surface of the diamond, where as FL diamonds will have no internal or external imperfections.
VERY, VERY SLIGHTLY INCLUDED (VVS1, VVS2)
Imperfections are extremely difficult to locate with 10x magnification and impossible to see without jewelers tools.
VERY SLIGHTLY INCLUDED (VS1, VS2)
Imperfections are difficult to locate with magnification and not visible to the naked eye. A layperson would have difficulty finding inclusions even with 10x magnification.
SLIGHTLY INCLUDED (SI1, SI2)
Imperfections are easy to locate with 10x magnification, but are very difficult (SI1) or difficult (SI2) to see without a jeweler's tools.
IMPERFECT (I1, I2, I3)
Imperfections are very easy to see under magnification and can be seen with the naked eye. Imperfect diamonds are more susceptible to cracking or breaking during daily wear. The majority of mined diamonds are of Imperfect clarity.