Rust is just about the worst thing that can happen to your cast iron. The flaky menace is iron oxide, a chemical compound formed through a chemical reaction between iron, oxygen and water. Left untreated, it will continue to corrode iron, making the surface more porous and brittle.
Recently, in our house, John and I joined forces against the Seasoned Dutch oven above. Tired dummy number one cooked a pot of dried rice and beans in it, and then tired dummy number two left it soaking in the sink, where it sat overnight. Whoops, wrong pot!
It looks bad, but really, it's no big deal. Our no fuss, no muss approach to rust:
Edited to add: We've gotten a lot of questions about this post! Your cookware will not rust easily and it needs to sit wet for some time to happen. Our cookware is no more likely to rust than any other iron cookware. (My mom accidentally ran her skillet through the dishwasher once and it came out fine - though your mileage may vary on that one!) The takeaway here is that even if there's been an oversight and you get rust on your skillet or Dutch oven, it's very easy to fix.
You are going to need to season your cast iron.
If you don't have the time to spare, wipe the affected areas with oil until you can deal with it. Rust can't continue to develop without access to oxygen (and the oil will seal it from the air).
Ready to start? You will need to get anything that can be wiped away off of the iron.
- Wash the iron with soap and water.
- If there is a lot of loose material on the surface, you'll need to scrub it off. I like to do this scrubbing under a layer of cooking oil to prevent newly bare spots from developing a rust haze on the surface.
- Once your iron is clean, dry it as much as possible and place it in a 200° oven until it is bone dry.
From here, you'll want to perform an oven seasoning, details linked! If you wish to, you can repeat the oven seasoning process several times, but it's not necessary. We find that cooking in your cast iron is the most robust way to build a nonstick surface.
Below, our Dutch oven after one round of oven seasoning and one pot of popcorn (obviously).
The color will deepen over time and even out as we cook in it and rebuild the seasoning.
A couple of notes!
- I generally do not find multiple rounds of oven seasoning worth the effort, but if you too have rusted out a Seasoned Dutch oven and mostly use it for bread, you should add another layer or two. Dry-baking doesn't allow for seasoning to build naturally through cooking.
- Sometimes a haze of surface rust will form that can be wiped right off. This "flash rust" can simply be sealed with oil without undergoing an oven seasoning process. Put a small amount of cooking oil on a cloth and rub it over the area.
- Do you use a tea kettle? Move your cast iron out of its daily steam-path!