Sudden rust issue in between coats of seasoning

[Charlie B]

I am very new to cast iron and refinishing (or attempting to). I have looked online and read a lot on this, many of the good advice was directly from this website.

I have done only 9 skillets with 7 still in the process of seasoning and 1 was a do over because I did not like the way it looked after 3 coats of seasoning. I thought all was going well until this morning when I had 6 skillets in the oven at 200F all of them with various coats of seasoning. After 20 minutes I took them out one at a time and applied another thin coat of grapeseed oil. This is when I noticed that a few of the skillets actually appeared to have a bit of rust that transferred to the blue shop towel that I was wiping the oil on with. It was not visible as the seasoning coatings are chestnut in color. One of these pans was on coat #7 and up to this point, I had not had this issue. One of the pans was on coat #2 and one on coat #5. All done with grapeseed oil.

I have looked all over online to see if I can find a reason for the sudden appearance of rust after this many coats but I am finding nothing. I hope to find an answer before going any further in case I need to start over. I would be very disappointed to try to cook in one of these skillets only to have rust.

I will describe my process and hopefully someone can find error with it or have an idea of what I did wrong this far along.

I am using an electrolysis tank to get the rust and crud off of these pans. I then take them inside and scrub any remaining spots and overall with very fine 0000 steel wool then use a green scrub sponge and dish soap and water to give them a final cleaning.

My fear is and was flash rust. Being new at this I did not want to have this happen so I tried to move fairly quick when removing from the E tank.

The first 2 skillets I read on a different website that you can use hot water to rinse and apply a coat of oil when its wet then put them in the oven at 200F for 20 then wipe off excess. This seemed to work ok and I did 3 coats of seasoning.

After the first 2 skillets I read that you can use very cold water to rinse then put in the oven at 200F for 20 minutes to dry then wipe on a light coat of oil. This method seemed easier so I kept with this.

When I apply the oil, I wipe all of it back off that I can with blue shop towel then the skillets go back in the oven at 470F for one hour. I turn the oven off after 1 hour at 470F and let the skillets come down to 200-225 range. I then apply another coat of oil and repeat.

This seemed to be working great with no issues. 2 nights ago I had applied the first coat to 2 skillets and the 4th and 6th coat. I let the oven run at 470 for an hour and shut it off and let the skillets cool inside till morning. This is the first time I did this.

I had put the 2 wet skillets that I removed from the E tanks in with the pans in the oven that were preheating for another coat of oil. The skillets were upside down like always and not touching. I had done this before one time as well adding a wet skillet to dry while the ones in the oven preheating with no issue. This was the first time putting 2 wet skillets in at once with the preheating pans but there was still plenty of room and airflow.

Thanks for reading this far and hopefully I described what I have done well enough that someone may be able to help me figure out where I goofed up.

I did go ahead and run these at 470F for an hour after wiping off rust with the oil then let cool 2 hours in the oven and they seemed to come out ok. I applied a very light coat of oil and back in for 20 minutes at 200F then wiped to see if I had any rust again. They were pretty good, a very slight wiped off one, only barely noticeable on the dry blue shop towel. I did not heat to 470F after this time I just wanted to see if the rust would happen again. Before I go any further hopefully I want to see if I need to re-strip these and start over.

Could it be the steel wool use and somehow I am not rinsing it all off after causing rust? Could it be adding the wet skillets to the gas oven when dry ones are in there is causing an issue? I am sure there are other possibilities as well.

I have 2 more in the tanks but I am going to leave the hang out until I can have some input.

This is definitely a fun and rewarding thing to do but I want to do it the right way so I am not giving my family skillets that they will have rust when they cook or bake with them. My Wife has been surprisingly patient with a kitchen full of cast iron for week and more sitting on the porch and I want her to have a good experience using cast iron skillets and for me not to get one upside the head.

Thank You for any and all help and advice.

 

[Charlie B]

To clarify, when I say I put the "wet" skillets in the oven to dry, I had towel dried them before hand so they were not dripping wet.

 

[Doug D.]

That's a lot to sort through, but I think what you're seeing on the shop towel may not be rust, at least not after you've applied a thin layer of oil, wiped off the excess and baked it to a dry state. It could just be oil that has become brown from heating.

Flash rust is just a thing that happens when bare iron meets any air with a level of humidity. It's not something to be prevented at all costs, avoided or feared. Any worth worrying about will wipe off with the excess oil you remove prior to baking. Even before baking, the thin layer of oil left should be a barrier that separates iron from air, so rust should not be forming past that point.

 

[Charlie B]

Thanks Doug, much appreciated! It definitely a long read and my apologies, I just wanted to paint a picture the best I could in case I could do something differently.

 

[C Carter]

This is a pretty old post but I would like to hazard a guess. When you put damp skillets in the oven to dry (even with a light layer of oil) and if you live somewhere humid like I do, I have found that I need to put a paint stirrer in the door to "just barely" hold it open during drying. This allows the evaporation to exit the stove, instead of just becoming a very hot sauna. I'm in Florida and I either dry my skillets - even well seasoned ones - on the stove top or in the oven with the paint stirrer at the top. It seems to help. After the pan is completely dry, then start your process as usual for seasoning.
Hope that helps someone.

 

[Charlie B]

This is a pretty old post but I would like to hazard a guess. When you put damp skillets in the oven to dry (even with a light layer of oil) and if you live somewhere humid like I do, I have found that I need to put a paint stirrer in the door to "just barely" hold it open during drying. This allows the evaporation to exit the stove, instead of just becoming a very hot sauna. I'm in Florida and I either dry my skillets - even well seasoned ones - on the stove top or in the oven with the paint stirrer at the top. It seems to help. After the pan is completely dry, then start your process as usual for seasoning.
Hope that helps someone.

Excellent information and this was exactly my problem. I did not realize how much moisture a gas oven or at least mine puts out at startup. I was trapping all the moisture in the oven with the pans. I switched to as you said, propping the door open while starting an empty oven and the entire preheating of the pans for 20 minutes or so. The issue of the rust residue is no longer. Thanks for posting that. I never thought to post a follow-up as to what solved my issue.

 

[Doug D.]

From the website article: https://www.castironcollector.com/seasoning.php

"Place the piece in the oven and let the 200° heat dry it completely, about 10 minutes. Leaving the oven door cracked open a bit during this initial heat-drying phase also helps to let moisture escape and minimize flash rusting."