the chance element in art?

i'm sure there was an art movement around that was purely based on chance element, for example it rings a bell to me, from a previous lecture donkeys months a go that some artists created collages by dropping the material on the page and this was purely what created the compostion of the collage. i think some also some artists just poured paint onto a canvas and that was then the artwork. I'm not sure whether there was a actual art group created for this, anybody know, Simon?

lbeastio