I was given a nice old 10" cast iron skillet from the 1950's. Only problem is the former owner sprayed it with WD40 in his garage so she wouldn't rust. Any chance of bringing it back?
I think what some folks are missing here is that oils etc can be very easily BURNED OFF, and if using the directly in the fire method even the carbon to which most things are reduced will be likewise burned away.
There is nothing left after such a treatment except "virgin" cast iron.