The old timers would clean their cast iron skillets periodically by submersing them in the hot coals of a wood fire, not while it
was burning brightly but after there was nothing but coals in the pile. They would cover the pan inside and out with the coals and often leave it overnight and then wash and re-season the next day and when it got too much of accumulation on the outside or they couldn't get the inside cleaned good, they would repeat the process which didn't have to be done very often. I have seen my mom and my grandmother both use this process. Sad thing is most of us do not have the wood fires of old with the coals these days. Wish I could use my cast iron skillets on my glass top stove, I loved those old cast iron and still have several of them and will not get rid of them until I die.