When does an egg shell harden?

Here's a breakdown of the process:

* Formation: The shell forms around the egg yolk and white inside the hen's oviduct.

* Calcium: The shell is primarily made of calcium carbonate, which is deposited in layers.

* Hardening: The shell hardens as the calcium carbonate crystallizes, forming a strong, protective barrier.

* Completion: By the time the egg is laid, the shell is fully hardened.

This quick hardening is essential for protecting the developing chick inside and for ensuring the egg can survive outside the hen.