The answer probably lies in the fact that, until shortly before they are laid, hens' eggs are white. The brown pigmentation associated with breeds such as the Rhode Island Red and the Maran is a last-minute addition during egg formation and, like a fresh coat of paint, can come off surprisingly easily.rnMore than 90 per cent of the shell of a hen's egg comprises calcium carbonate crystals bound in a protein matrix. The shell starts to form after the egg has reached the uterus, where it stays for around 20 hours prior to being laid.
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