The GIA and AGSL use a standard set of rules in determining gem clarity.  The clearest gems are considered the most valuable and are exceedingly rare at the clearest levels.  The existence of impurities that cause less clarity are called inclusions.  Inclusions can be scratches, or trace minerals.  Inclusions are carefully considered for there number, location, and size. The contrast of the inclusions is integral to their observability. The quantity of inclusions and where they are located is very critical.  A few inclusions near the edge of the gem will provide for much better viewing than a few inclusions near the center.

Diamonds are graded meticulously by the GIA and AGSL.  They have adopted the following grading systems:

FL, IF Diamonds: Flawless: No internal or external flaws.  Internally flawless: No internal flaws. These diamonds are extremely rare and beautiful.

VVS1-2 Diamonds: Very, very slightly included: Very difficult to see inclusions under 10X magnification. This is regarded as an excellent quality diamond.

VS1, VS2 Diamonds: Very slightly included and not typically visible to the naked eye.

SI1-2 Diamonds: Slightly included: Inclusions are visible under 10X magnification, and may be visible with the unaided eye. These diamonds are typically a good value.

I1, I2, I3 Diamonds: Inclusions can easily be seen by the naked eye.