A diamond that is virtually free of interior inclusions or exterior imperfections (commonly referred to as flaws) is of the highest quality as there is nothing that interferes with the passage of light through the diamond. To determine a diamond's clarity, it is viewed under 10x magnification by a trained gemologist. Small inclusions neither mar its beauty nor endanger its durability.
FL - Flawless - No internal or external imperfections.
IF - Internally Flawless – No internal imperfections.
VVS1, VVS2 – Very, very slightly included: Very difficult to see any inclusions under ten power magnification.
VS1, VS2 – Very slightly included: Inclusions are not visible to the unaided eye.
SI1, SI2 – Slightly included: Inclusions are readily visible under ten power magnification but usually not visible with the unaided eye.
SI3 – Slightly included per European Gemological Laboratory: This grade is not recognized by the Gemological Institute of America (GIA) and would be graded either SI2 or I1. SI3 diamonds may have white imperfections visible to the unaided eye. But in most cases, no black imperfections readily visible.
I1 – Included: Inclusions that are visible to the unaided eye.
I2, I3 – Included: Inclusions that are readily visible to the unaided eye. The diamond may appear black, cracked or hazy.