Clarity is probably the trickiest of the 4C’s. A diamond’s clarity is determined by the number and size of natural imperfections and/or blemishes found in and on the stone. In the industry these imperfections are referred to as inclusions. Most of these inclusions are so teeeeny tiny you would never be able to see them with the naked eye. The GIA clarity scale contains 11 grades: Flawless (FL), Internally Flawless (IF), Very Very Slightly Included (VVS1, VVS2), Very Slightly Included (VS1, VS2), Slightly Included (SI1, SI2), Included (I1,I2,I3).
Flawless (FL) - No inclusions or surface marks are visible to a skilled grader using 10× magnification
Internally Flawless (IF) - No inclusions and only superficial surface marks are visible to a skilled grader using 10× magnification
Very, Very Slightly Included (VVS1 and VVS2) - Inclusions are difficult for a skilled grader to see under 10× magnification
Very Slightly Included (VS1 and VS2) - Inclusions are minor and range from difficult to somewhat easy for a skilled grader to see under 10x magnification
Slightly Included (SI1 and SI2) - Inclusions are noticeable to a skilled grader under 10x magnification
Included (I1, I2, and I3) - Inclusions are obvious under 10× magnification and may affect transparency and brilliance
If you are looking for a diamond, don’t get TOO hung up on the clarity. As long as the imperfection is not visible to the naked eye, you are good to go. If you go for a diamond that is VS2 or above, you are pretty much guaranteed an eye-clean stone. Once you step into SI1 territory and below you will definitely want to see the diamond in person.
The SI clarity range is by far the broadest. In many instances, you can get an SI clarity diamond that is completely eye-clean, making the stone an amazing value. Other times you can have an SI clarity stone where the imperfections are visible to the naked eye. I would not recommend purchasing a diamond with eye-visible inclusions as the value is highly diminished.
Also, keep in mind the importance of clarity differs between diamond shapes. For instance, if you are looking for a brilliant cut diamond like a Round, Cushion, or Radiant try to stay above an I1 clarity. If you are looking for a step cut diamond like an Emerald or Asscher cut, you will want to stay above a SI1 clarity (just because the inclusions will be easier to see with the step-cut faceting).
As with everything in life, there’s usually a trade off- whether it be substituting a higher color for a lower clarity or a larger carat weight for a lower color. All of these compromises are totally fine, as long as you know what you are getting before signing on the dotted line ;)