Best way to clean rusty cast iron?

I once took one a very old one to an autobody shop and had them sandblast it clean.

@HellonKitchen: Yes, you are correct -- running a cast iron pan through the oven cleaning cycle will strip all the seasoning off, as I mentioned in my post. That is the goal -- to start fresh. Your suggestion is also a good one for less serious rust. How to proceed just depends on the condition of the pan.

Thanks, everyone. I have a couple of older skillets I've had forever, so I now general maintenance just not revival. I think I'll have to try the onion. I love that idea. Then I'll just do a regular scrub and season as I do with my others. Thanks again.

I disagree with cookbookchick. Don't ever run your cast iron pans through the oven cleaning cycle, you will strip off all the seasoning on there. I would first fill the pan with an inch or so of water and bring to a simmer for about 10 minutes, then cool. Drain and remove any remaining rust with a sponge - no soap here! scrubbing as needed with the synthetic scrubby side. Rinse and wipe out the pan with paper towels. Return pan to the stove and heat over medium until completely dry, several minutes. Add enough vegetable oil to cover the surface with 1/2 inch of oil. Heat over medium high heat for another 10 or 15 minutes. Let cool. Once cool, discard the oil and wipe with papertowels leaving a thin film of oil in the pan. For stuborn spots you can sprinkle pan liberally with course Kosher salt and scrub with the cut side of a lemon half. Then procede as above. I have my great grandmother's deep cast iron pan which I treasure. It has never seen one soap sud...

I have lots of cast iron and treasure (and use!) each piece. I have found that running the pans through my oven's automatic cleaning cycle works well. I place them on the floor of the oven taking care not to touch the heating elements. This cleans them and takes them down to the unseasoned metal, so you will need to re-season the pans before using them. Obviously, if you have six pans that need work, you won't be able to do them this way all at once. Once they are re-seasoned, frequent use and proper care will produce a beautiful black finish that is virtually non-stick.

Score!

We certainly love our cast iron. There have been a few sad stories detailed here, but even the saddest ones have had great outcomes.

http://www.food52.com/foodpickle/2227-i-got-a-cast-iron-skillet-from-a-friend-and-i-need-to-season-it-unfortunately-it-has-rust-all-over

http://www.food52.com/foodpickle/954-cast-iron-cookware-i-have-a-cast-iron-skillet-and-a-dutch-oven-my-boyfriend-is-an-absolute-dumpli

http://www.food52.com/foodpickle/478-can-u-save-a-cast-iron-pan-that-has-become-rusty