The acid dissolves the outermost layer of the rock therefore causing all the stuff that is stuck to the outermost layer to just fall off (which on Pukani rock is a lot of stuff). I tried bleaching a few pieces and it barely removed anything. I only let irt soak in the bleach for about an hour and nothing got removed that I could tell whereas the acid took it all off in half the timestill don't understand why people recommend acid. You really want bleach to oxidize the organic