In my experience you need some sort of mild acid to wash the copper rolls....hot vinegar works well and gave good results, I just can not stand the smell of vinegar unless its in a jar of pickles or kraut. I use dilute phosphoric acid obtained from a janitor supply place in town. Probably any dilute acid other than sulphuric would work (would clean but it would beat hell to get all the sulphur byproducts out and hence turn your product blue)