The clarity of a diamond is graded according to the size, number, discernability, appearance, nature, position, type and influence of inclusions or lack thereof within the diamond.
When we talk about a diamond's clarity or flaw-grade, we are referring to the presence of tiny, usually microscopic, imperfections. As it forms in nature, every diamond develops inclusions. They might be cracks shaped liked feathers or minute diamond crystals, or even crystals of some other gemstone! Each diamonds internal picture is unique and no two are alike.
Identification and classification of these clarity grades are determined by using a 10x magnification loupe under correct lighting.