The majority of the black crusty crap on the pan was ages-old layers of carbonized oil. Likely the customer was using a poor oil choice for higher temperature frying and cooking, like EVOO, which would cause more and more layers to build up over time.

I got a large 44gal tote and filled it about to where it could cover the pans, then added sodium hydroxide crystals to it. Exact measurements vary on quantity of water, ambient temperature, length of soaking, etc. NEVER ADD WATER TO SALT, start with water then salt after.

The lye bath got rid of the majority of the gunk, and using a wire scouring wheel on an electric drill (WITH GOGGLES ON) finished the job.

Following this, I seasoned with two layers of homemade ghee.