Clarity refers to the absence of internal flaws or inclusions. Type and placement of flaws are also very important. Sapphires almost always contain inclusions and even quality sapphires are lightly included. If you find a flawless stone, you would be wise to question whether it is synthetic or an imitation. Nature almost never makes sapphires, rubies or emeralds without inclusions.
Dark sapphires show fewer inclusions but lack the fire and brilliance of their lighter counterparts.
Sapphires should be eye-clean at wrist length with slight inclusions visible under a 10x scope. Nearly everyone wants the most perfect gem, but perfection in the precious colored gems may be impossible. The common unit of measurement for gemstones is weight and is expressed in carats. Do not confuse weight with size. Some stones weigh more than others because stones have different density.