I have burnt some badly burnt on food in a very old cast iron frying pan. It was handed down to me from my Mother, and it has great sentimental value, but I can’t remove the black residue.
Cast iron pans are fantastic, and they will last forever! A properly seasoned cast iron pan has similar properties to modern non-stick coatings, with the added benefit of being renewable, and also having the ability to withstand metal utensils. The first task would be to clean off all that carbonized material. There are cleaners available that contain sodium meta silicates, which work very effectively, and are found in most commercial food service environments. However, they are very caustic, and dangerous to work with, so a less chemical reliant solution might be preferable. Try putting the cast iron pan in your oven during a self clean cycle. Alternatives would be to place it into a camp fire, or fire place for a few hours, or to get some BBQ briquettes, fill the pan and light them up (outside of course) to burn off the carbon residue. The pan may need to sit for several hours to cool enough to handle, but bear in mind, the hotter the iron is when washing, the cleaner it will get. At this point, wet sand, or an abrasive scrubber work most effectively to loosen the remaining material from the pan. Finally, wash the pan in hot soapy water, rinse thoroughly, and dry immediately.
If you are seasoning a new pan, you have to wash it with HOT soapy water to remove the thin wax, or oil film that protects the pan from rusting. Some experts even suggest that after rinsing, and drying with a towel, the pan be dried over a flame or in a heated oven for a couple minutes to remove ALL of the moisture.
Turn on your oven to 300 degrees and add some Crisco to the pan. Do NOT use liquid vegetable oil. After about 15 minutes, remove the pan, and be sure the sides also have a coating of oil. Pour out the excess, and return the pan to the oven to “bake” for two hours.
Avoid acidic foods like tomatoes or beans, as they will damage a weak or newly seasoned finish. If not properly seasoned, cast iron pans will drip dark liquid into food. If this is the case with your pan, you will need to re-season it.
It is best to clean cast iron pans while they are still hot, by washing with hot water and a nylon pot scrubber. Abrasive scrubbers and soap will remove the seasoning. Always dry the pan thoroughly, and store without the lid in place, or with a paper towel inside to absorb any moisture.