The purpose of the wash is to remove all traces of oil and prepare the surface to accept the bluing. Once you have it prepped and dried it, the bluing is applied and then removed on the high spots, the reason that the .3 micron film is used instead of polish is so that it does not go down into the grooves of the etch and pull the bluing out. If you use polish it will remove more of the bluing than you really want.