Mike’s Brain

Rheoscopic fluids allow you to current flows — think of a bottle of pearlescent shampoo.
Paul Matisse created a number of Kalliroscopes, which use rheoscopic fluid to display fluid flow.  Info on Matisses’s work, and has rheoscopic fluid for sale. 
www.kalliroscope.com (Warning – horrible Java menus!)
Another source - Pearl Swirl Rheoscopic Concentrate from Steve Spangler Science