There are many factors that affect the overall quality of the egg shell, but before discussing these factors, it is important to know what makes up the structure of the egg shell. The egg shell consists of about 94 to 97% calcium carbonate.
The other three percent is organic matter and egg shell pigment. There are also as many as 8,000 microscopic pores in the shell itself. The outer coating of the shell itself consists of a mucous coating called the cuticle or bloom which is deposited on the shell just prior to lay.This protein like covering helps protect the interior contents of the egg from bacteria penetration through the shell.
Egg shell quality is determined by the color, shape, and structure of the shell. Colors can range from white to tints to brown and egg shape can also vary.