EVAPO-RUST works at a pH of 6.1 to 7 (neutral) through selective chelation. This is a process in which a large synthetic molecule forms a bond with metals and holds them in solution. Most chelating agents bind many different metals. The active ingredient in EVAPO-RUST bonds to iron exclusively. It can remove iron from iron oxide, but is too weak to remove iron from steel because the iron is held much more strongly.