Inherited cast iron skillets have rust under gummed up oil
I've inherited some Lodge cast iron skillets -- non-enamel (just plain old cast iron). I've read quite a few forum threads about how to restore them, since one had rust and the other two had gummed up residue in thick layers on them. So I've set to work scrubbing off the gummed up stuff (with sand paper, not using any water), 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!