Ferrofluids are extensively used for the study of magnetic domain structures in magnetic tapes, rigid and floppy disks, magneto-optical disks, crystalline and amorphous alloys, garnets, steels and geological rocks.

Commercial applications include the quality control of magnetic recording media and the identification of micro-defects in steel.

Ferrofluid is applied to the magnetic tape, disk or other specimen so that a thin layer of ferrofluid covers the surface. When the carrier liquid evaporates, the particles congregate at the domain boundaries. These appear as dark lines in visible light and can be viewed with a microscope. A small external magnetic field can be applied to the specimen to enhance the contrast of the pattern.

The EMG series of ferrofluids, which includes both water and mineral oil based fluid, has been developed specifically for this purpose. Domain detection kits which include samples of different ferrofluid, wetting agent and solvent are also available.