An egg shell that is smooth is preferred since rough-shelled eggs fracture more easily and have poor appearance. Eggs with extremely rough, or uneven shells are downgraded to B quality. Some eggs have a rough pimply appearance. The pimples (calcium deposits) are distortions to the shell. Infection is not responsible because pimpling also occurs in disease-free flocks. The defect may be partly hereditary.
Mottled shells have pale translucent spots (sometimes called "windows") of various sizes. Such eggs appear normal when laid. The mottling develops later and may be noticeable half an hour after laying, although it is more easily detected a day later. This abnormality is inherited, although a similar effect can be induced artificially, such as when a wet, newly laid egg slides across the wire cage floor instead of rolling, or when a hen's toenail scratches the surface of a recently laid egg.