It is very common for diamonds to be formed with slight imperfections. These are known as "inclusions" and can come in many forms, including tiny white points, dark dots, or feathery cracks inside the diamond. The fewer inclusions, the more the stone is worth. A diamond's clarity ranking is determined by the number, size, type and placement of the inclusions. External characteristics are called "blemishes." Inclusions have a higher impact on the clarity grade than blemishes.
Clarity grading in diamonds uses the criteria of 10x magnification (10 - power eye loupe) with the stone face-up. The fewer imperfections, the more valuable the diamond is.
A stone with only a few hard-to-see pinpricks located near the edge, where they can be covered by the mounting, has better clarity than a stone with a crack located right under the table (the large top facet of the stone). Cracks from the surface to the interior are especially dangerous because the diamond could break if hit the wrong way. On the other hand, small nicks and chips on the surface are often of little concern because they can be polished away.
For the most part, diamonds used in jewelry are clean to the naked eye. In a certified diamond, the cracks are charted on the certificate and act as a fingerprint for identifying a particular stone.
When determining a clarity grade, five factors are considered:
Size - The relationship of the size of the characteristic to the size of the diamond
Nature - The type of inclusion and its relationship to durability. Feather, fractures and cleavage can grow if enough stress is generated. Though these inclusions may be less noticeable, their durability will be a big factor
Location - The relative ease with which a characteristic can be seen due to its position in or on the diamond
Number - The relative quantity of characteristics found in or on the diamond
Color - The amount of characteristics found in or on the diamond
The following is the GIA clarity scale, along with corresponding definitions for different clarity grades, which is very commonly used in the United States:
||Free from all inclusions or
blemishes at 10x magnification.
||No inclusions visible at 10x,
insignificant surface blemishes.
||Difficult to see face-up at 10x.
||Easy to see at 10x.
||Easily visible to unaided eye.