I've used electrolysis to clean up several cast iron pan flea market finds. It works great. All you need is a car battery charger, a large plastic container (I use an old kitchen garbage can), a piece of rebar, and some washing soda.
http://antique-engines.com/electrol.asp

-Blast

p.s. Do it outside and don't smoke. It release quite a bit of really flammable hydrogen gas.