craftgrrl | what's this activity called?

i was going to ask my ex this question, but i decided he's not nice and i never want to talk to him again, so:

i did an art project when i was a kid, that involved covering a canvas randomly in paint, then finding shapes in it and painting the details onto it, using the random mess as inspiration.

i'm working at a summer camp and i want to do a similar thing with the campers, except we're going to make the random mess with mud, because mud is fun.

according to my housemate, there is a name for this process of making art out of random mess that he learned at art school, but he can't remember it. anyone know what he means?