Ferric Chloride Etching Solution: Hematite Dissolved in Spirit of Salt

Ferric chloride solution etches copper: it turns the bare copper into soluble chlorides that rinse away, leaving the covered pattern, as on printed circuit boards and etched metalwork. Dissolve powdered hematite, the red iron ore, in hydrochloric acid; the solution comes out brown. It is corrosive: gloves and goggles. The picture: a brown solution of iron(III) chloride.