Brand new carbon steel pan produces grey residue. (I know it’s normal, but what actually is it?)
I purchased a brand new carbon steel pan, and followed the instructions to wash off the protective layer then briefly dry it on the cooktop before applying a thin layer of grapeseed oil. Afterward, the paper towel I used to apply the oil appeared to have picked up a fine grey residue.
The paper towel on the bottom right was used to apply the oil to the carbon steel. For comparison, I repeated the exact same process on a stainless steel pan using the paper towel on the lower left, which has a much more natural light-brown staining, as I would expect from a little grapeseed oil. The paper towel in the background is clean and untouched, for contrast in the photo.
I‘ve searched everywhere online and can’t find a reliable explanation for this, either on carbon steel forums or manufacturers’ websites. There are literally tons of posts like this on this subreddit already, and I’ve browsed as many as I had time for, but I haven’t run across a genuine explanation, though theres a lot of well-intentioned and educated hypotheses. I know it’s normal, and I’m not concerned about it, but it’s still so weird and counterintuitive to someone like me that’s never cooked with anything other than stainless.
My best guess is it’s some kind of oxide like magnetite that formed between the time the pan was formed and the factory applied their protective coating. But that’s 100% guesswork until i find a reliable source that confirms or disproves it.
Anyone have any leads? Shot in the dark, but I’d love to know.