important basics of diamonds clarity:

Diamond clarity is used to illustrate the in-existence or existence of flaws that are internal or the external part of a diamond. It is rare to find a perfect stone that possesses perfect clarity or clearness and most of the flaws that exist in jewelry grade diamonds cannot be seen without bare eyes, but by looking at it through the magnifying loupe of the jeweler. Clarity is one of the qualities that you should consider before buying a diamond.

What SI2 stands for?
SI2 means Slightly Included while others call it Slightly Imperfect but they all mean one thing, that is – the Diamond possesses Small Inclusions in it, the tiny imperfections which are mostly small.

The difference between SI2, SI1 and VS
SI1 is the higher end of the SI Clarities that is closer to the VS Clarity while the SI2 is the lower end of the SI range (according to GIA). VS Category diamonds are also known as the Very Slightly Included category. These diamonds have tiny inclusions which are very hard to be seen with 10 times the magnification by a trained grader.

How a good SI2 diamond is defined by?
Small inclusions – these are the inclusions such as clouds, feathers, crystals or minerals, knots, cavities, cleavage, bearding or internal graining that can hardly be seen by the naked eye.
White/natural color inclusions – these are the inclusions that do not exactly modify the original color of the diamond.
Well positioned – they are located at the side or bottom of the diamond where they will be not so visible.
Spread – inclusions are scattered evenly so it can not be that obvious.

What is a wrong SI2 diamond?
Dark color – the inclusions are basically black or grayish in color that can make them visible when the diamond is examined.
Large – inclusions can be easily seen by the naked eye.
Concentrated – inclusions are concentrated in one place where it can be so visible.
Badly positioned (surface, mirror effect…) – inclusions are mostly located in the heart and crest of the diamond where it can be easily distinguished.

How to avoid from buying the wrong SI2 diamond?
Understand the basics – know the basic facts about what you are about to buy.
See the diamond or see a real view picture – if buying online, check out some TRUE pictures of the diamond you wish to purchase,or visit a diamond store to have a close look.
Certified – before buying, make sure that the diamond was certified by a reputable lab.
Trusted seller – go to the seller that you know you can trust.