I've inherited some cast iron pieces, and I've read quite a few threads on CH about how to deal with them. Armed with that info, I've set to work scrubbing off the gummed up stuff that was layers thick on these skillets, and under all that I'm finding an orange layer. I'm assuming this is rust? I didn't realize it could grow under the oil. Do I need to scrub until all the orange is gone? Or am I just scrubbing till the surface feels flat, and then oiling and heating them to re-season? Thanks!