There is a substance out there called a ferrofluid. It is quite possibly one of the coolest things ever. Ferrofluids are metals that exist in a liquid form, but when a magnetic field is applied, they solidify into neat shapes and patterns. They're generally composed of tiny particles of compounds that contain some amount of iron, such as hematite or magnetite. The particles are tiny enough to be suspended in a liquid. They were developed by N.A.S.A. in the 1960's and are now being used in a variety of applications, including engineering, electronics, medicine, the military, and art.