Clarity refers to the amount, degree and placement of inclusions within a diamond, as viewed under 10x magnification. Because diamonds are formed inside the earth under high heat and pressure, very few are naturally flawless. The closer a diamond is to flawless, the more rare and expensive it is.
Flawless (FL): Free from all inclusions or blemishes, at 10x magnification.
Internally Flawless (IF): No inclusions at 10x; insignificant surface blemishes only. Note: Once a Flawless stone has been mounted, it can only be graded as Internally Flawless
Very Very Slightly Included (VVS1 and VVS2): Contain minute inclusions, that are difficult for even a skilled grader to locate under 10x. In VVS1 stones, they can usually only be seen through the pavilion.
Very Slightly Included (VS1 and VS2): Contain minor inclusions ranging from difficult (VS1) to somewhat easy (VS2) for a trained grader to see under 10x. Small included crystals, feathers and clouds are typical.
Slightly Included (SI1 and SI2): Contain noticeable inclusions ranging from easy (SI1) or very easy (SI2) to see under 10x. Most inclusions are not visible to the unaided eye, but some may be visible through the pavilion.
Included (I1, I2, I3): Contain obvious inclusions to a trained grader at 10x, can often be seen face-up with the unaided eye, seriously affect the stone’s durability, or are so numerous they affect transparency and brilliance. In I1 stones, the appearance or durability is moderately affected, in I2 stones, the appearance or durability is severely affected, and in I3 stones, the appearance and durability are severely affected.