20 December 2010 at 19:26 #15379
Because it can stain and is usually wanted for demonstrations, it is now available in a bottle containing alcohol. (This allows a blob of ferrofluid full movement near a magnet but prevents it sticking to the glass wall).
A strong magnet is needed to get the hedgehog effect. The oil does stain quite easily and badly!
There are lots of good pictures on the web: