The clarity grade of a diamond is determined by the presence, or lack, of internal inclusions and external blemishes under 10-power magnification. Diamonds with very minute internal characteristics are very rare.
Diamonds graded Flawless to SI1 are known as "eye clean" meaning that their internal inclusions are only visible with the aid of a microscope. SI1 diamonds represent excellent values. Cross' diamond buyer cherry picks the best, always looking at each diamond under the microscope before it becomes part of the Cross Collection.