Electrolysis cleans away rust like magic, and you can set up a simple system in your shop with a battery charger and a few household items.
A simple system consists of a shallow container, a battery charger, rebar, a short copper wire, a clothespin and washing soda.
This gunky water is actually quite safe, although I wouldn't use it to mix cocktails. It can be dumped down any drain.
I read about this rust removal technique in American Woodworker magazine several years ago and decided to give it a shot. It seems like something you’d see on “MythBusters,” but guess what? There's no myth busted here; it really works. I'd like to explain all the neutrinomistic-plasmotical physics involved, but, um…I just don't have the space, so I'll just tell you how to do it.
You'll need a plastic or glass container deep enough to hold enough water to cover your rusty item. And you'll also need a battery charger, a box of washing soda (found with the laundry detergents at just about any big grocery store), a short copper wire and some rebar bent to fit around the object you're restoring. Hook everything up as shown and walk away. Tomorrow morning you'll be amazed to see how rust-free Grandpa's old hatchet is. It gets rid of most of the rust, but you'll still need to polish with sandpaper, steel wool or Scotch pads to get down to bare metal.
When your kid comes home telling you about the science fair project, baby, you are ready! Only you still have to figure out that science-y stuff for the display. And by the way, don't e-mail me for help with that—I'm really busy.