Rust Question

[Scott.L]

I use an E-tank and it does a fair job at breaking down rust, however i have noticed that it tends to leave a black almost powdery feeling residue. I use dawn, white vinegar, barkeepers friend, magic eraser, more dawn, steel wool, and green 3M all in separate stages. I get to a nice grey surface but 2 minutes later it is a bull black again and generally has a much more metallic odor during seasoning cycles. Is this a normal reaction for cleaned skillets with rust issues?

[Doug D.]

From: http://www.castironcollector.com/electrolysis.php

"The process of electrolysis converts red rust (ferric oxide) to ferrous oxide, sometimes called black rust."

Ferrous oxide is a form of iron oxide that, unlike rust, is soft, black and is easily rinsed off. Just wash with Dawn, rinse, dry thoroughly and proceed with your manual seasoning regimen and you'll be fine.

[Scott.L]

Doug,
is it normal for the ferrous oxide to return after being scrubbed off ?

[Doug D.]

As long as there is O2 and ambient humidity contacting the iron, there will typically be some kind of oxidation forming. Even though average relative humidity is high where I live, I haven't experienced the red "flash rust" phenomenon all that much. But drying a cleaned pan with towels normally transfers a black residue from an apparently clean pan that must be the "black rust". Some find it to be a positive and heat the pan to a high temp before manual seasoning to deliberately create it and jump start the darkening process. I really don't care about that too much one way or the other, but just know you don't need to drive yourself crazy trying to eliminate it because it probably won't totally stop. It's not really a cause for concern. The action of wiping off the first coating of manual seasoning oil will take most of it with it, and the thin layer of oil left will "seal" the iron from the air.

[Scott.L]

Doug,
Thank you; it had been worrying me on a few pans i was working for a friend. I would hate to give them a poorly restored skillet.