I had some given to me that were pretty cruddy. I lit the charcoal grill and put them in it, closed the lid and left it overnight. In the morning when everything had cooled, the crud was all burned off. I reseasoned them and use them to this day. YMMV
'93 Jayco FS3500 TT behind a '92 Dodge D250 powered by 5.9L Cummins
'94 Vogue Prima Vista powered by 8.3L Cummins w/ 6spd Allison
A elderly lady down the street ask Me if I would like to have all Her black iron cook wear. She said it was to heavy to handle any more. I took it! The problem is: She never washed the outside. It has a crust at least 1/4 inch thick. Inside is cleaned and seasoned well. What can I do to get the crust off short of using a jack hammer?
Don't clean the outside, the baked finish keeps it from rusting.
The same reason you don't wash it in soapy water.
When I season a piece, I do it inside and out. Enjoy.
The neighbor must think a lot of you to give you her Cast Iron.