The clarity of a diamond is determined by the number, location and type of inclusions it contains. Inclusions can be microscopic cracks, mineral deposits or external markings. Clarity is rated using a scale which contains a combination of letters and numbers to signify the amount and type of inclusions. This scale ranges from FL to I3, FL being Flawless and the most valuable.
The process of the growth and creation of a diamond inside the earth does not occur evenly, but in several phases. In each phase, the conditions such as temperature, pressure and cooling are not the same and do not always remain constant. As a result, most diamonds contain what are called inclusions, internal features caused by the constantly changing conditions during different phases of the diamond's creation. These inclusions come in many forms including cloud-like features, fracture or tension cracks or even enclosed minerals that were present during the growth process of the diamond.
The GIA (Gemological Institute of America) has designated that clarity of diamonds is graded under the following guidelines:
FL:
Diamond free from internal and external flaws under 10X magnification.
IF:
Absolutely free from internal faults under 10X magnification. May contain external features that should be so small that they can easily be removed by polishing.
VVS1:
Very, very small inclusions in the stone, very difficult to recognize under 10X magnification. These inclusions can not be in the field of the table.
VVS2:
Very, very small inclusions anywhere in the stone, only smallest external defects allowed.
VS1:
Only the smallest inclusions are allowable in the field of the table and only small faults elsewhere in the stone.
VS2:
Very small internal faults. Small external defects.
SI1:
Small internal faults, not visible to the naked eye.
SI2:
Small, easily seen inclusions under magnification in the table, but still not visible to the naked eye.
I1:
Inclusions easily seen under magnification, but difficult to see with the naked eye. Inclusions do not influence brilliance.
I2:
Large and numerous inclusions, just barely visible to the naked eye through the crown. Inclusions slightly diminish brilliance.
I3:
Large and numerous inclusions, easily visible to the naked eye, dimishing brilliance.