Different ceritifcates institutions have differents Clarity Chart nominations.
The GIA has established an internationally accepted system according to which Clarity is graded from Flawless to Imperfect. Flawless diamonds are the most rare and as such they are considerably more expensive than the lower-rated, Imperfect diamonds.
Diamond clarity is divided into six categories, most of which contain several grades of clarity. As the clarity grade moves along the scale from higher to lower, the overall value of the diamond decreases. However, even though the clarity grade may drop, it might not necessarily affect the unmagnified appearance of the stone.
The table below defines the various levels of clarity in the GIA clarity scale for both white and colour diamonds.
The clarity grades from highest to least are as follows (simplified):
IF (Internally Flawless): No internal inclusions under x10 magnification but may have minor external blemishes.
VVS1/VVS2 (Very, Very Slight Inclusions): Inclusions very difficult to see under 10x magnification.
VS1/VS2 (Very Slight inclusions 1): Minor inclusions still difficult to see under 10x magnification.
SI1/SI2 (Slight Inclusions 1): Inclusions that can easily be detected under 10x magnification.
I1/I2/I3 (Imperfect): Inclusions visible to the naked eye when viewed through the top of the diamond.