(1) A "clean" shell is a shell that is free from foreign material and from stains or discolorations that are readily visible.
An egg may be considered clean if it has only very small specks or stains, if such stains or specks are not of sufficient number or intensity to detract from the generally clean appearance of the egg. Eggs which show traces of processing oil on the shell are considered clean unless otherwise soiled.
(2) A "dirty" shell is an unbroken shell that has dirt or foreign material adhering to its surface, which has prominent stains, or has moderate stains covering more than 1/4 or the shell surface.
(3) A "check egg" is an individual egg that has a broken shell or crack in the shell but with its shell membranes intact and its contents do not leak. A check is considered a lower quality than a dirty.
(4) A "practically normal" (AA or A quality) shell is a shell that approximates the usual shape and that is of good, even texture and strength and is free from rough areas or thin spots. Slight ridges and rough areas that do not materially affect the shape, texture and strength of the shell are permitted.
(5) A "slightly abnormal" (B quality) shell is a shell that may be somewhat unusual in shape or that may be slightly faulty in texture or strength. It may show definite ridges but no pronounced thin spots or rough areas.
(6) An "abnormal" (C quality) shell is a shell that may be decidedly misshapen or faulty in texture or strength or that may show pronounced ridges, thin spots, or rough areas.