I recently was given an old family cast iron skillet and noticed that the outside of it had serious buildup. Basically I can take my fingernail and lift several, thick, black pieces off. The inside of the pan is fine. I was wondering where this comes from and if this affects cooking on the pan. Also what would be the best way to remove the buildup? Thanks
The inside looks absolutely fine, so assuming you will protect that if you do any actual work on the outside I see a couple of routes you can take...
You can ignore it & see if it will reach a new equilibrium with your own cooking equipment & technique.
You can clean it off & quite quickly return the outside to a lesser seasoned state - as you're not cooking on the outside the seasoning is far less important, & as you've already discovered, the outsides of pans can get a lot more build-up over time than the insides*.
You could attack it with sandpaper, or a drill & wire brush attachment, though you need to beware of the mess that can make if you do it indoors... or you could take it to somewhere that could shot-blast it for you. This is an industrial cleaning process, depending on abrasive type can be extremely vicious, but it's rapid & they could clean the outside back to shiny iron in 2 minutes.
You can then re-season the outside.
*You should have seen my old wok before my partner threw it away. I eventually forgave her ;)
Placing the pan in the oven during a self cleaning oven cycle will make the peeling layers turn to ash, and they can be easily scoured off using a steel wool scrubber. (Tried this from experience with a pan very similar to yours)
Unfortunately, this will require re-seasoning the entire pan.
I am always looking for things to break out my dremel....iT would work perfectly on a cast iron pan that has build up...In fact you could used several different attchments to really take off the black bumpy stuff....I would have a ball if I had a cast iron skillet that was old and needed this I have it looking new in no time at all and you could too !! grab your dremel and get to work !