These GIA diamond grading scale can be further understood as follows:-
FL-Flawless: The diamonds in this grade do not show any internal or external flaws, under the 10x loupe magnification.
IF - Internally Flawless: The diamonds that fall in this category have no internal flaws and only slight external blemishes.
VVS:Very ,Very Slightly included The diamonds that fall under this grade have minute inclusions that are very difficult even for a skilled grader to see under, 10X magnification. Pinpoints and needles grade at VVS. The VVS category is further divided into two grades. VVS1- These are excellent quality diamonds. The miniscule inclusions may not even be visible under 10X magnification. VVS1 is better than VVS2.
VVS2: Beautiful brilliance and high quality, these stones have very, very small inclusions.
VSI: Very Slightly Included These diamonds come with minor inclusions that are hardly visible under 10X magnifications. Generally, the inclusions present in VS diamonds are invisible without the magnification. The VS category is divided into two grades.
VS1: The inclusions are not at all visible to the naked eyes though can be traced under 10X magnification. They make a good purchase with better quality with value.VS1 is better than VS2.
VS2: These stones have very small inclusions. Rarely there is a possibility that diamonds that fall under this grade have inclusions visible to the eye.
SI: Slightly Included The diamonds that fall under this category have evident inclusions that are visible to the trained grader under 10X loupe magnification. Diamonds in this grade are good in quality and less expensive. Primarily, The SI category is divided into three grades.
SI1: The diamonds in this grade have inclusions that may or may not be noticeable to the naked eye.
SI2: These stones have inclusions that may be visible with the naked eye.
Si3: These stones have inclusions that can be visible with the naked eye.
Diamonds have obvious inclusions that are clearly visible to the trained gemologist even without magnification. These inclusions may be easily detectable without magnification affecting the brilliance and the durability of the stone. ‘I’ category is divided into three grades.
I1: Inclusions present in the diamonds falling in this grade are visible to the unaided eye.
I2- Diamonds in this grade have inclusions that are noticeably visible.
I3: The inclusions in the diamonds of this grade are quite conspicuous, affect the brilliance of the diamond and threaten the structure of the diamond.
Colorless and near-colorless diamonds are the most valuable. Though most diamonds may appear colorless to the naked eye, the majority of diamonds contain slight traces of yellow or light brown when viewed under a jeweler's loupe. Depending on the stone's size, a single increase in color grade can boost the value of a diamond by thousands of dollars per carat. A traditional engagement diamond is usually colorless or near-colorless.
In nature, diamonds can also occur in shades of red, pink, blue, green and deep yellow - These are called "Fancy diamonds". In the United States and around the world colorless diamonds are graded on an alphabetical scale, introduced by the Gemological Institute of America (GIA). "Colorless" or "rare white" diamonds are of color grades D, E and F. Diamonds of color grade D are very rare, and extremely valuable.