Electrolysis is a technique for returning surface rust to iron. It uses the effect of an small low voltage electric current and a suitable electrolyte (solution). It has advantages over the old standbys, like vinegar, Coke, muriatic acid, Naval Jelly, wire brushing, sand blasting etc -- These methods all remove material to remove the rust, including un-rusted surfaces. With many, the metal is left with a "pickled" look or a characteristic color and texture. The electrolytic method removes nothing: by returning surface rust to metallic iron, rust scale is loosened and can be easily removed. Un-rusted metal is not affected in any way.
What a good idea... now get rust busting...