Diamond clarity is one the 4Cs of diamond qualities. It refers to any flaws, or inclusions in the diamond, and how visible or detectable they are. Inclusions can be foreign substances, or minute cracks or flaws. It also refers to the appearance of any surface flaws or scratches. As with the color grading scales, clarity also has a grading scale, with FL used to denote a flawless diamond. What FL means is that there are no flaws or inclusions that can be seen when the stone is examined under 10X magnification, the standard for examining for flaws.
Other clarity designations are:
IF stands for internally flawless. This means there are no internal flaws or inclusions, although there may be small surface flaws.
VVS1 and VVS2 stand for Very Very Slight inclusions that are difficult to see under magnification. VS1 and VS2 indicate Very Slight inclusions that can be seen under magnification but are invisible to the naked eye.
SI1 and SI2 denote Slight Inclusions that may or may not be visible to the naked eye.
I1, I2 and I3 are "imperfect", with inclusions clearly visible to the naked eye. For I3, the inclusions impact the brilliance of the diamond and are large and obvious.
In most cases, there is nothing that can be done about flaws or inclusions, although in recent years lasers have been used to enhance some inclusions or fractures in diamonds by filling them in, much the way small dings in a windshield are filled in.
Certainly the most highly valued diamonds are those that are flawless – FL - or internally flawless – IF. But excellent values can be obtained at the VVS and VS grades, as these are flaws not visible to the naked eye, but only to an experienced grader under magnification.