Numbers 31:22-24

22only the gold, the silver, the bronze, the iron, the tin, and the lead,

23everything that can stand the fire, you shall pass through the fire, and it shall be clean. Nevertheless, it shall also be purified with the water for impurity. And whatever cannot stand the fire, you shall pass through the water.

24You must wash your clothes on the seventh day, and you shall be clean. And afterward you may come into the camp."