Clarity grade refers to amount and severity of internal and on-the-surface flaws of a diamond, called inclusions and blemishes, respectively. The flaws are judged when viewed with x10 magnification, under industry-standard viewing conditions.
Inclusions can be small fractures (also called "feathers"), crystals ("piques"), and minute particles forming together a cloud-like appearance ("clouds"). Blemishes include deep scratches, cavities and small penetrated crystals of diamonds ("naturals", "knives" or "knots"). Colorless or colored internal growth marks ("graining") may be present too.
The GWLAB laboratory's clarity scale includes twelve grades ranging from Flawless to Included (or Imperfect). The clarity grading scales are given in the following Table, as viewed by a skilled observer, under favorable lighting conditions after thorough examination with a binocular microscope at ten power magnification and with a 10x corrected loupe:
Fracture in a diamond
|Flawless||This grade is used to describe a diamond that does not include any inclusions or surface blemishes, under the above conditions. Small extra facets on the pavilion near the girdle, not visible when viewed from above, are permitted as are small naturals when they are confined to the girdle and do not flatten the girdle's outline. Internal graining is permitted, provided it does not draw any color or texture and is not observable through the crown.|
|Internally Flawless||This grade describes diamonds which have no inclusions or possess minor surface blemishes that do not penetrate the stone. Surface grain lines are permitted provided they are not too thick or numerous so as to detract from the beauty of the stone. Internal graining is permitted, provided it does not draw color or texture.|
|Very, Very Slightly Included (VVS1 or VVS2)||These grades are used to describe diamonds which have very, very small inclusions which are difficult to see under the above conditions. Colored or textured graining is permitted, provided it is not observable through the crown.|
|Very Slightly Included (VS1 or VS2)||These grades are used to describe stones with very small inclusions which can be difficult to observe under the above conditions. Except for larger stones or occasionally with Emerald cut diamonds, these are rarely visible to the unaided eye.|
|Slightly Included (SI1, SI2 or SI3)||These grades are used to describe stones with small inclusions which are usually obvious when viewed under the above conditions. The SI3 is a unique clarity grade for EGL. It is a step grade between SI2 and I1 and represents the "top quality" of I1-graded stones.|
|Included (I1, I2 or I3)||These grades are used to describe stones with medium or large inclusions (Piques) which are usually obvious to a skilled observer with the unaided eye under favorable lighting conditions.|