http://www.wag-society.org/Electrolysis/lye.php
Basically what a few above have said. I've restored countless old pieces ranging from no-name oldies to Griswold/Wagner/Piqua etc. You can do a lye bath (be CAREFUL of your skin/eyes) to remove everything except the rust first (as long as needed, you can't hurt it in the lye bath), then rinse well and do a a 50/50 water/vinegar to get the rust off. You're ok to go up to 12-18 hours if need be on the vinegar solution, just SOFT wire brush it occasionally as it goes. Then rinse VERY well to neutralize the vinegar, warm in the oven to dry, and season as you like. I prefer lard since I use mine all of the time.