I'm seeking the name of or reference for an experiment I once saw in a college physics class. At the beginning of one class the instructor repeatedly wound a wiper that spread a blot of some type of ink all over the interior of a glass jar. Then during the lecture (which I admittedly don't remember very well) he must have explained something about the second law of thermodynamics or entropy and that once a large system gets all mixed up, there's really no chance for it to return to its original state. Then he concluded the class by winding the wiper in the opposite direction, and clearly to his delight our jaws all dropped---the film of ink, which had been spread all over the interior of the jar, reappeared in the original blot.
Surely, there are folks on this site who demonstrate this every semester. What on earth is this experiment?