Leviticus 15:12

And the vessel of earth, that he toucheth which hath the issue, shall be broken: and every vessel of wood shall be rinsed in water.

The vessel of earth ... shall be broken. It is thought the pottery of the Israelites, like the earthenware jars in which the Egyptians kept their water, was unglazed, and consequently porous, and that it was its porousness which, rendering it extremely liable to imbibe small particles of impure matter, was the reason of the vessel touched by an unclean person being ordered to be broken.