The Flawless Grade (FL) is used to describe diamonds in which a skilled observer, under favorable lighting conditions, cannot see any inclusions or surface blemishes after thorough examination with a binocular microscope at 10 power magnification or with a 10 power corrected loupe. Small extra facets on the pavilion neat 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 outline. Internal graining is permitted provided it does not draw any color or texture and is not observable through the crown.

The Internally Flawless Grade (IF) describes diamonds which have no internal characteristics observable under the same conditions as described above, but which have minor surface blemishes that are confined to the surface. Grain lines are permitted provided they are not thick or numerous and do not detract from the beauty of the stone. Internal graining is permitted, provided it does not draw color or texture.

The VVS Grades (Very Very Slightly Included) are used to describe diamonds which have very, very small inclusions which are difficult for a skilled observer to see under the conditions as described previously. Colored or textured graining is permitted, provided it is not observable through the crown.

The VS Grades (Very Slightly Included) are used to describe those diamonds with very small inclusions ranging from difficult to somewhat easy to observe under the 10 power magnification and favorable lightning conditions.

The SI Grades (Slightly Included) are used to describe those stones with small inclusions which are easy or very easy to see under 10 power magnification and proper lightning. Occasionally, inclusions in the SI category are visible to the unaided eye.

The I Grades (Included) are used to describe stones with medium or large inclusions which are usually obvious to the unaided eye under favorable lightning conditions.

Every diamond is unique, with a distinctive pattern of internal and external identifying characteristics. The skilled diamond grader takes into consideration the size, nature, locations, and number of these characteristics to assign each.