Here we hold a magnet beneath the glass, close to the ferrofluid. We can see how the spikes form and how the spikes follow the magnetic field lines of the magnet. The stronger the magnetic field the denser and more pointy these spikes become.
Normally, fluids are not ferromagnetic, which means they are not attracted by a magnet. When you manage to get tiny iron particles floating in a fluid without clumping together or sinking to the bottom, then you have a ferromagnetic fluid that reacts to a magnetic field, a so-called "ferrofluid". If you then place a super magnet near the ferrofluid, you can watch all sorts of weird behaviour. Ferrofluid is typically only industrially used, for instance during the production of loudspeakers. In our webshop, you can get the ferrofluid in small bottles with a pipette so you can make your own experiments with this fascinating fluid.