Should I cook in the old carbon steel skillets I just bought at a flea market? And can I use them for campfire cooking? I just bought two carbon steel old pans, numbers 43 and either 6 or 9 (orientation?), at a flea market. One of the skillets has a lot of burned on flaky black very hard something - outside, mostly, on sides and bottom, and some around the top edge of the inside sides. I need to clean them, but they appear to be seasoned okay. The super hard stuff on the outside and inside has me worried. How can I clean that off and start out well?

Also, I bought them to use over a campfire, on a grill grate, so they won't rest on coals or wood. Is this acceptable for carbon steel, and if so, are there any parameters for heat or closeness to the fire? 

At home, I cook almost completely on cast iron and coated cast iron. Are cast iron and carbon steel skillets the same basically in regards to seasoning and cooking on electric, or should I use them more like stainless steel?
You can season these pans by heating with salt in the pan until it is extremely hot. The salt is abrasive and will remove any particles when you rub it around the pan with a dry cloth. Be very careful as the salt is very hot! This opens up the pores in the steel. Remove the hot salt and ad some veg oil, olive oil or what ever you have and let it season the pan. The pan should now be non stick and the heat has sanitized the pan. Remove the oil and wipe with a paper towel.