Even though I'm late also, let me chime-in since I love Cast Iron. If you can wait or don't have time to go camping or nowhere to build a fire. Soak the cast in a tub of white vinegar in your garage and it will remove all rust etc. It does take some time though. The fast track is to buy some phosphoric acid at the Hardware store, perfectly safe, it's in all sodas and won't kill you or blind you like muriatic acid. Be warned that phosphoric acid smells horrible when it reacts with iron. I think you can add a current by dropping leads from a car battery and it will make the process go even faster, though I've never tried the eloctrolysis method mysellf