How did rust appear on my cast iron in a matter of minutes?

Question

So this has been an on-going saga the last few days, and I've already posted several related questions here, and I am feeling quite defeated.

I have/had a beautiful 16" cast iron dutch oven from Cabelas. I took it out for a test spin the other night (I had completed all seasoning steps that the Google Gods recommended). Then:

• I tried (and failed spectacularly) to cook a pork roast in it, but cooked it at way too hot a temperature and burned/charred/fused the animal fats/juices into the oven, whereby it basically baked into the cast iron (related question here)
• I tried cleaning/scrubbing it with coarse-grained salt -> did nothing
• Then I tried cleaning it with dishwashing liquid + salt -> did nothing
• Then I let the whole thing soak in a vat of a 50/50 mixture of water + white vinegar -> took all the tarry slude off, stripped some seasoning off (revealing bare iron), but in 80% of the burned/charred areas, still did nothing
• Then I went to town on it with a steel wool and salt and dishwashing liquid and was left with some smooth, properly seasoned surfaces, and some more areas stripped down to bare metal
• I decided to just re-season it. So I scrubbed it one last time (about 1 hour ago) with a steel wool and some water, got all the rust and remaining crud off (finally), and built a fire.
• I placed it on the hot coals of the fire and let it sit there for 15 mins. My intention (whether misled or not) was to burn off all the remaining water from when I had previously washed/scrubbed it, then let it cool off, then season it with oil, and then bake it for a few hours.

So I just took the oven off the fire and opened the lid...and the entire inside is covered in rust. An hour ago there was none. When I put the oven into the fire 15 mins prior, there had been none (yes, I checked) This just came out of nowhere.

I'm ready to give up, unless anyone can offer some concrete set of steps for me that will salvage this $100 rust bucket. How can I get rid of the rust and then re-season this before more rust sets in? Meh...

Answer 1

The problem with your last step was the lid, I think.

If you had placed it on the hot coals, open, the heat should have driven the water off as you intended, drying the pot before it rusted. With the lid on, the moisture was trapped inside, and had opportunity to cover every inch of the metal - and, as Joe mentioned, heat speeds up the reaction. Sitting on the heat with a coating of water, and you have a layer of rust. Not functionally different that if you'd tried boiling a pot of water before seasoning it. The seasoning is, after all, supposed to protect the bare metal from water so it doesn't react like this when being cooked in.

How to fix it - go back two steps. Scrub off the rust, or as much as will come off easily. I agree with paparazzi, here, if it won't come off while scrubbing it will probably not come off while cooking - especially under the seasoning. Once it's well scrubbed, dry it off. You might use a towel or something first, but if you're going to put it on the fire, leave the lid off so the moisture can escape the pot.

You might have the lid drying to the side, leaning against the outside of the pot, or partially on (generously offset) if you want to dry the lid as well. You probably don't need to heat it for long, either, just until it looks dry - and it will be evaporating water all the way until it cools down, too. When I'm re-seasoning my frying pan, I heat it only 10min or so, and by the time it cools it is usually dry (disclaimer, I use the stove rather than coals, so your timing may vary).

After that, you can smear it with a layer of oil and re-season. wipe it down with oil, and heat to re-create the layer of seasoning that got scrubbed away in the first place.

Beyond that, it will probably help to calm down a bit. In the future, just remember to keep the lid off when drying, and that you don't need to panic quite as much. Cast iron is pretty sturdy, and scrubbing down to the metal and re-seasoning is always an option until the pot is worn away to holes.

Answer 2

I realize that I am a year late to respond, but I just found a solution to your exact problem. Perhaps it can help someone else.

1) When you scrub off the rust (my cast iron was totally stripped of seasoning, so I used warm soapy water and steel wool), you must IMMEDIATELY towel-dry it. This is critical! If you put it in the oven to dry it, the heat causes it to rust much more quickly than it dries. (Note: I stripped mine by putting it in the oven and using self-cleaning mode. It totally destroyed all built-up gunk and most of the rust, and I just used soapy water to rinse and get a little remaining rust)

2) Once it is dried off, check and make sure it is a dark grayish color all over with minimal red. Large spots of rust should be scrubbed again, but some faint red coloring has never hurt my cast iron and disappears once they are seasoned.

3) As soon as you towel-dry it and checked that all rust is gone, apply the first thin layer of oil for seasoning (don't wait - this invites rust) and pop in the oven (I do an hour at 250 degrees F). Most sites I used suggested applying about three good layers of seasoning before storing the cast iron.

It sounds like your problem was trying to dry the cast iron with heat instead of a towel. I hope you were able to save your dutch oven!

Answer 3

Oh, I'm sorry to hear about this latest frustrating development!

If this dutch oven is truly cast iron, I don't believe there was a factory applied "protective coating" on it. The only protective coating a cast iron pot needs is the seasoning of baked-on oil which you will be applying to it. Even if there had been some kind of NASA-inspired teflon coating that you removed with the steel wool, then, yes, it is now gone, and you are left with a wonderful old-fashioned cast iron dutch oven like the ones that people have been using for forever (with no space age coating on it).

It is true that rust can form on cast iron very quickly, especially if it is hot. Even though it is seasoned ok (at least I am happy with it), my cast iron frying pan gets a little rust on it if I wash it with water & don't bake it dry right away. But I just wipe the rust away, put some oil in the pan, and fry away.

It sounds like maybe you have more than just a couple thin smears of rust on this thing. Did you possibly put it on the fire with a little water in it and the lid on? Making steam? (which would really rust up the place)

In any event, without wasting too much more work on this project, how about removing as much rust as comes off easily, and if the surface is still smooth without a lot of deep pits and holes, then just go ahead & try seasoning it & see what happens. Follow the seasoning directions that probably came with it.... They didn't really tell you to season on a roaring campfire did they? Even if they did, I would try a more moderate temp. Does the dutch oven fit inside the oven of your kitchen stove? The instructions that Lodge sent with my frying pan specified baking with oil inside the oven at a temp that sorry I forgot, but pretty easy to look up on line I'd bet.

If the inside surface is so rusted out that it is deeply pitted and raggedy, then, hmmm, my advice is the same as paparazzi (look in thrift store)

Answer 4

A mechanical stripping is rarely good enough when it comes to cast iron. If you need to strip everything, you have to either burn it off or strip chemically, preferably with lye because it is food safe.

Also, never use salt for cleaning unseasoned iron. You can use it for seasoned pans, although you risk corrosion if your seasoning layer is not perfectly sealing everywhere.

It is absolutely normal for iron to rust quickly under the right conditions, so heat and the presence of acid or salt. The solution is to strip the rust just like seasoning, with lye (maybe the heat of a self-cleaning cycle works too, I've never tried). You can mechanically separate some of the rust first, but that won't spare you the lye bath.

After that, simply reseason. We have quite a few questions on how to do it.

Answer 5

I am having the same thing happen to a frying pan I am taking down to bare cast iron to re-season. I ran it through the self-cleaning cycle on my oven. After washing and drying on the stove burner, it was covered with a thin coat of rust. I just found out that it is called "Flash Rust." I just found this YouTube video that makes sense and I am going to use these instructions:

https://www.youtube.com/watch?v=wW2iJizDVsA

It shows scrubbing it down to bare (gun metal colored cast iron) with white vinegar first, washing the vinegar off with soap and water, then drying it immediately and quickly applying a coat of oil or Crisco to prevent the Oxidation/Flash Rust from recurring. Then you can proceed to replace the seasoning a layer at a time at your convenience. I would use an oven to control the temperature for re-seasoning. There are many YouTube videos on how to restore seasoning on cast iron. I hope that helps.

**I just finished adding 4 layers of seasoning to my skillet, and it is turning out perfectly. No residual rust. When I added that first coat of seasoning after the vinegar wash, I did have some brownish/rust color on my cloth that I was using to oil the pan - it didn't seem to have any negative effect or remaining rust after the first seasoning in the oven. Just wanted to update.

Answer 6

I never use any chemicals in my cast iron equipment. When the cooking is done, I just boil water for a minute or two in it and wipe it with a clean dish brush and then I let it self dry.

Never experienced any rust

Answer 7

Evidently there was a protective coating on the dutch oven you scrubbed off. I don't think you are going to get it back.

In hind site you were worried too much about getting the crud off. If it will not come off with a good regular cleaning then it is not going to come off and contaminate the next food you cook. You should have tried just cooking with it.

Rust is not poisonous. You could try cooking with rust and see if it taints the food.