You know that bowl of water beside your pickle that you dunk
your piece in after you pickle it?? After a period of use, it
becomes rather acidic. Not as acidic as the pickle, but acidic
enough to be difficult to neutralize with baking soda. Tried it.
Along with that acidity comes dissolved copper. If you will
notice, the water that is beside your pickle has a blue hue to
it. This is copper sulfate. Now, if you had a steel implement
or some steel filings or anything steel in it, a plating reaction
would occur. There is enough copper dissolved and enough acid
there to provide a electrolytic plating bath. Weak, but enough.
Marshall T. Jones @Marshall_Jones