If you have something rusty, you can get a wire brush and a lot of elbow grease. Or you can let electricity do the work for you in an electrolysis tank. [Miller’s Planet] shows you how to build such a tank, but even better, he explains why it works in a very detailed way.
The tank uses a sodium carbonate electrolyte — just water and washing powder. In the reaction, free electrons from the electrolyte displace the oxygen from the rusted metal piece. A glass container, a steel rod, and a power supply make up the rest.
For an example, a rusted sliding door piece was put in the cell. The steel rod became very rusted, of course. The piece came out looking pretty bad because the rust residue was caked on it, but it wiped right off leaving a pretty clean looking piece after an hour. He thinks leaving it in longer would have produced an even better result.
You should not use stainless steel for the steel electrode because stainless contains a toxic form of chromium (although one commenter mentions this is not an issue — we aren’t sure if it is a problem or not). He also warns you to be sure to be outdoors or under ventilation because the process will form hydrogen gas and you don’t want a repeat of the Hindenburg disaster in your shop.