As diamonds form deep underground and under extreme pressure and heat, imperfections can form in the crystal structure and trap mineral impurities within the stone.
The size of these impurities and imperfections determine the clarity grade of a diamond. Diamonds without such impurities are extremely rare.
The grading scale ranges from Flawless/Internally Flawless (FL/IF), Very Slightly Included (VVS1/VVS2), Very Slightly Included (VS1/VS2), Slightly Included (SI1/SI2) to Included (I1, I2, and I3). Diamantwerp does not sell diamonds below SI2 as they are not considered suitable for jewelry. In general, diamonds graded VS2 are more likely to have inclusions visible to the naked eye, but this varies from stone to stone.