I first saw this stuff in a (very tangential) physics demo. I Then tried to take a picture of with the camera I was using at the time. (a medium format pin hole with an f/200 lens) and failed. This set comes from playing with the stuff for a day with 35mm film and a 100m macro lens. I would like to shoot more of it, but the liquid is expensive, messy, and the professor I borrowed it from is on sabbatical. (Serious Thanks to Prof. Moore).
Ferrofluid is made by dissolving magnetized iron fillings on the order of nanometers into a liquid. Kerosine and Vegetable oil work. When a magnet is placed near the fluid it erupts into the shapes seen above. Those shapes represent the lowest potential energy of the fluid as a whole. (that's as much as I understand). One more thing, don't drop the magnets into the fluid, it makes a huge mess, and is extremely difficult to then get off. This was the one condition of borrowing them from Moore, it was an accident worth photographing. I am not sure if he knows that I did drop them in.