Ferrofluid is one of the neatest things to see in action. Suspending liquid through the use of magnets? Super neat! Ferrofluid is a colloidal suspension of ferrous, which contains iron, and a liquid. (Some kind of oil since we all know what happens when you mix water and iron).
There are generally two ways you can make ferrofluid. The more expensive way (around $100 per cartridge of magnetic primer toner and some vegetable oil), and the cheaper way which is a little more difficult to make, but will only cost you about $10. You’ll need about 10 cassette tapes, some acetone, a strong chemical resistant bucket (this is very important), plastic wrap, vegetable oil, and magnets. Earth magnets are the better choice because neodymium magnets aren’t as good at stripping ferric oxide off of the tapes. To make, you’ll want to step outside as inhaling acetone is not favorable. You’ll break apart your cassettes and throw the tapes in your chemical resistant bucket. You’ll mix your acetone in, cover it with plastic wrap, and let it sit for an hour. When you come back you’ll have a fine black powder in the bottom of the bucket, and your tapes will look clear now. Wrap your magnet in plastic wrap and push your tapes to the side. Collect the ferric oxide with the magnet and place the powder in a small container off to the side to dry. Once it’s dry, add your vegetable oil (approx. 1.5 tsps of vegetable oil to 1 tsp of ferric oxide) and then you have your ferrofluid!