The clarity of a diamond refers to the presence or absence of flaws. There are two types of flaws called inclusions and blemishes.
Inclusions are internal flaws. They appeared during the formation of diamond, a gemstone composed of carbon which crystallizes. The inclusions are unique for every diamond. These « fingerprints » make it possible to recognize a diamond among others diamonds. There are many types of inclusions: clouds, feathers, crystals or minerals included in the diamond, knots, cavities, cleavage, bearding and internal graining.
Otherwise, blemishes are external flaws. They can be natural or can occur during the cutting process. There are different forms of blemishes : polish lines, grain boundaries, scratches, nicks, pits and chips.
Furthermore, the number, size, color, relative location, orientation and visibility of inclusions and blemishes can affect the clarity of a diamond. A diamond with no or few inclusions are rarer and highly valued than those with less clarity.
However, the clarity of a diamond can be enhanced with treatments. A laser can be used to remove some types of inclusions. And tiny cracks in a diamond can be filled with a colorless substance.
To evaluate the clarity of a diamond, the GIA, Gemological Institute of America, observed diamonds under 10x loupe magnification and created a scale:
Internally Flawless named IF is a category of gemstone which have no internal inclusions but eventually few external flaws.
VVS1, VVS2, the abbreviation of Very Very Slightly Included are regrouping diamonds which have flaws very difficult to see.
VS1, VS2, the abbreviation of Very Slightly Included, designed flaws not easily seen.
SI1, SI2, for Slightly Included, regroup flaws which are easily visible.
I1, I2, I3, for Included, is the last grade of diamonds whose flaws are visible to the naked eye and affect their appearance.
Generally, jewelers recommend to buy a diamond with a grade higher than SI2.
The best clarity (F, IF) don’t improve the appearance of a diamond, compared to a grade like VVS1 or VVS2. In fact, a diamond of grade SI2 look exactly the same to the naked eye than a diamond of grade VVS1.
Moreover, a higher grade of clarity don’t assure that this diamond are the most beautiful. Other criteria are essential like carat, color and cut. These characteristics and clarity are representing the four Cs of diamond grading.