Inclusions in a diamond are features visible inside the stone that were generated by Mother Nature billions of years ago during the crystal's development under extreme heat and pressure.
Flawless (F) is the highest clarity grading for diamonds. When an expert diamond grader examines a flawless diamond at 10X magnification, there are no flaws or defects evident. Internally Flawless (IF) is the second highest rating, which means there are only minor superficial imperfections but no inclusions visible under 10X magnification.
The ratings that follow are:
'Very Very Slightly Included' (VVS1 and VVS2),
followed by 'Very Slightly' (VS1 and VS2).
The next diamond grades down the scale are 'Slightly Included' (SI1 and SI2) and finally 'Included' (I1, I2 and I3).
Under 10X magnification, VVS graded diamonds generally have minute inclusions no larger than the tiniest pinpoint.
Minor inclusions are more visible in VS diamond grades than in VVS diamond grades, although they are still small even under 10X magnification.
SI grade inclusions are larger and easier to spot under magnification; yet, SI clarity ratings can often be a buyer's best friend if the diamond is completely eye clean and the imperfections are well-placed. With these requirements, a stone can be as bright as a flawless diamond while costing a fraction of the price.
Inclusions visible (I1) to the naked eye and noticeable under 10x magnification are present in "I1, I2, and I3" clarity diamonds (Included). Inclusions in I2 and I3 stones are frequently noticeable and have a negative impact on the stone's brilliance, beauty, and durability.
According to the GIA, a diamond's Clarity grade is determined by five variables. Size, Scope, Position, Nature, and Relief are the factors to consider. Clarity grade and value are determined by the size and quantity of inclusions as well as their position in the stone. An inclusion situated closer to the stone's edge [girdle] will be more noticeable and less attractive than one located under the table. Furthermore, because diamonds are highly reflective, if an inclusion is deep and too close to a pavilion facet, it tends to reflect around the stone like a house of mirrors, lowering its desirability and value.
The type of inclusion also makes an impact on value. Inclusions that break the surface of a diamond have considerable impact on durability and value and should be avoided.