Can you season over some thin flash rust and get a usable pan as a result? What are the downsides of doing so?
I've had a carbon steel pan with some thin flash rust spots. I've tried to remove them by scrubbing, but after applying a new layer of seasoning it turned out I hadn't removed all of it.
While I find a lot of posts online about how to remove rust from pans and how to prevent rust in pans, I can't find a clear answer to the question whether a thin layer of rust under layers of seasoning is actually harmful. The way I see it, once there's enough seasoning on top of the rust there won't be any oxygen for the rust to expand and the surface that touches your food is free of rust.
What are the downsides when you have some flash rust in a carbon steel pan and continue seasoning over it until the pan stops giving off rust when rubbed with an oily paper towel?
Some of the problems I can imagine happening (but I'm not sure if they will happen):
The seasoning won't hold onto the pan as well as it would without the flash rust.
The new layers of seasoning won't 'grab onto' the rusty parts meaning that you will never arrive at a point where the existing rust is trapped inside layers of seasoning. In other words, when rubbing it with an oily paper towel the pan will always continue giving off some rust.
Best Answer
An iron pan is one single piece of substance. It just stays the way it was cast.
A patch of rust is a brittle, powdery substance. It will crumble with time, pieces of it falling off, no matter if they have a bit of seasoning on top or not. So, you will end up with these spots being "naked" again.
Additional to that, in any kind of applying coatings (in the kitchen and outside), "hiding" pieces of other stuff under a coating (even if it is "just" an old patch of the same coating you are applying) is a hallmark of shoddy work. The integrity of your new layer is compromised, and you get quality problems over time. Any professional painter spends more time sanding away old paint than applying new one. It is just a physical property of coating layers that they require an even surface with known-good qualities. If you want a good coating on your pan, you will have to do the stripping work.
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Can I season over flash rust?
A patch of rust is a brittle, powdery substance. It will crumble with time, pieces of it falling off, no matter if they have a bit of seasoning on top or not. So, you will end up with these spots being "naked" again.What happens if you season over rust?
In addition to posing a potential health risk, rust on your cookware can negatively affect the flavor of your food. Using rusted cookware is not a good idea, especially if it's a pot or pan that you use very frequently. With all of this in mind, it's best to play it safe when you're dealing with rust.Can you use a pan that has rust on it?
Regardless of the extent of rust, there are options beyond throwing out rusted cast iron. For severe rust that covers most of the cookware surface, take the piece to a machine shop to have it sandblasted and restored to raw cast iron, then season immediately.No More Flash Rust
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