This is Ferrofluid. Invented at NASA, by Steve Papell in 1963, it is a liquid with bits of iron in it that will align along magnetic fields! Usually, it is kept inside of a container, often suspended in a clear liquid. Here, we let some of ours out to play!
The ferrofluid isn’t dangerous, although it does leave a nasty stain on skin and clothing, much like it is on our platter here, but it was well worth it!
Magnetic fields are an often mystifying concept, because of the inability to see it in normal circumstances, but with the addition of ferrofluid, it becomes much more obvious! In our setup here, the iron sphere is attached to two strong neodynium magnets, and becomes highly magnetized. The ferrofluid that made it to the sphere is condensed on the areas where the magnetic field is the strongest, allowing the magnetic field to become visible close to the magnet! We can now see something that is normally invisible!
While it seems exotic, ferrofluid is found in all kinds of everyday things, including speakers, transformers, and hard drives!