What is Philosopher’s wool?

The compound zinc oxide (ZnO) is called philosopher’s wool. Alchemists, as part of their rituals, would burn zinc in air and collect the residue, which formed into white woolly tufts. They called it lana philosophica in Latin, meaning philosopher’s wool. Zinc oxide has many uses: as white pigment in paints, component in zinc ointment for treating skin diseases, material in sun screens and sun lotions, in rubber manufacture and in photocopying products.