Have heard of this, but thought it was just a myth, and did not want to scratch up the chrome with the foil, but you prompted me to research, and was impressed... - from the article...
Oxides are the key
Cleaning Rust is basically oxidized metal or another words metal that has taken on extra oxygen atoms. As heat is generated by the friction of rubbing the aluminum foil on the chrome, a portion of the aluminum will oxidize to produce aluminum oxide. Aluminum has a higher reduction potential (i.e a tendency take on electrons and in the process reduce or break itself down) than the chrome, and will therefore leech oxygen atoms away from any rust on the chrome surface which changes the chemical properties of the rust and breaks it down.
Aluminum oxide is harder than steel, and the microscopic grains of aluminum oxide produced during the cleaning process creates a fine metal polishing compound which, mixed with the water you added, creates a paste that smoothes and polishes the chrome surface.
Another thing to add to my list for J.D.
and maybe that means... just maybe, .... no need to tar anymore... :confused04:;