These four qualities of diamonds are called the 4 C's of diamonds. Of these, the diamond's clarity depends on certain characteristics that the diamond acquires during its formation and retains even in the polished state.
They are as good at identification as fingerprints or retina scans, which are unique identifying marks for the humans.
Pinpoints: This is a very commonly seen characteristic. This is a very tiny crystal that is embedded inside the diamond. It looks like a pinpoint of light when the diamond is viewed under magnification of 20x and more.
Cloud: This characteristic is used to describe the presence of a small group of pinpoints. You may expect to find a cloud containing three or more pinpoints in close proximity. If the cloud covers a third or more of a diamond, it may affect the light reflecting inside the diamond, and its external brightness and, consequently, value.
Needles: These are thin, long crystals embedded inside the mother diamond. The tremendous pressures to which a diamond is subjected during the process of formation, makes these crystals acquire a long and thin shape rather than a circular shape, in which the crystals are commonly found.
Knot: This is the characteristic that is used to describe a crystal that is embedded inside a diamond and extends to its surface. Such a knot in a diamond is considered a risk from the point of view of the durability of the larger diamond.
Chips: The chip is nothing but a blemish on the surface. A small impact can mark a diamond by breaking off a tiny part off its surface.
Feather: A crack or a minuscule fracture inside a diamond is referred to as a feather in the trade. If it extends to the surface of the diamond, it puts the durability of the diamond in question. It is not considered as much of a risk as knots, though.
Diamonds are graded according to GIA's (Gemological Institute of America) Clarity Grading System.
To determine the blemish or the particular inclusion in the diamonds, they are viewed under 10x magnification under controlled lighting.
According to the GIA Clarity Grading System a diamond can be graded in 11 diamond clarity ratings or grades that range from flawless or internally flawless(FL or IL), VVS1 and VVS2 (Very, Very, Small inclusions), VS1 and VS2 (Very Small), SI1 and SI2 (slightly included), I1,I2 and I3 (Included diamonds).
Many of these characteristics are visible to the naked eye, especially in the case of included diamonds, while flawless diamonds do not show any problems even under the magnification.