Make Your Own Ferrofluid for Fun and Science

Ferrofluid is liquid containing a suspension of ferrous (iron) material — usually very fine iron powder or shavings. Often, special surfactant coatings help to keep the particles from clumping together. As iron is magnetic, ferrofluid responds to magnetic fields. That is useful for visualizing magnetic fields, as the liquid will conform to those fields if they are strong enough to overcome gravity and surface tension. You can buy jugs of commercially made ferrofluid, but it can get pretty pricey. An alternative is to follow this Instructables tutorial from Zujus to make your own ferrofluid.

To make his ferrofluid, Zujus turned to a ready source of affordable ferromagnetic material: cassette tapes. Those tapes, used both for audio and general data storage, encode information through magnetic polarization. A cassette recorder’s writing head sets the polarization and strength of flexible tape containing magnetic particles. A cassette player’s reading head translates the tape’s local magnetic fields into an electric signal. Because cassette tapes border on obsolescence today, they are very cheap (and maybe even free) to acquire in large quantities. A typical tape doesn’t have any real monetary, sentimental, or historical value, so nobody will get upset about you destroying it for this purpose.

The goal here is to harvest the iron oxides from the magnetic tape. To do so, you’ll need to separate those particles from the flexible plastic tape film. Zujus devised a process that is easy and affordable to follow at home:

Start by breaking apart a bunch of cassette tapes to gather the rolls of tape. Then put them in a tub (that isn’t made of ABS plastic) full of acetone. Cover the tub and let the solution do its magic for a few hours, giving it an occasional shake or stir. Then remove the congealed tape roll gunk.

This process should dissolve the tape enough to release the iron oxides, which will then disperse through the acetone. You can collect those ferromagnetic particles using a strong magnet wrapped in plastic and dragged through the acetone. Scrape those particles off the magnet and let them dry, and you’re left with a fine ferromagnetic powder. Mix that with some cooking oil and you have a ferromagnetic fluid.

This DIY ferromagnetic fluid won’t perform as well as the commercial stuff, as it lacks surfactant coating to reduce clumping. But it should work well enough to visualize strong magnetic fields. It is particularly useful for school science experiments.