Cast iron frying pans can last a lifetime if properly cared for. However, cast iron will rust if not seasoned and prepared properly. If your cast iron frying pan is starting to rust or you just want to keep it in good shape as you use it, follow these steps.
With a new cast iron frying pan, season it after purchase. All new cast iron cookware comes with a factory-applied coating that needs to be removed before using it. Scrub the pan (and its lid if it has one) with a kitchen scrubber and a little dish soap. This will be the only time that you will ever use dish soap on your cast iron. When you've thoroughly scrubbed it, heat the pan on the stove over high heat until every drop of water has vaporised. Heat the lid on a separate stove element. Let the pan and lid cool until they can be handled.
With a paper towel, wipe vegetable oil onto the pan, covering every inch inside and out. Rub oil into the inside of the lid as well. Wipe off excess oil from both the pan and the lid. Store the pan with its lid off until ready to use.
After cooking with your cast iron frying pan, remove food immediately. This helps speed cleanup and stops the food from absorbing too much iron. If some food is stuck on the pan, soak it for no more than 15 minutes in hot water, then proceed to Step 4.
Clean your cast iron frying pan properly after each use. Allow the pan to cool down slightly before washing. Never put cold water into a hot cast iron pan or the iron could crack. Pour a few spoonfuls of table salt into the pan and scrub with water and a kitchen scrubber or nylon brush--the salt helps scrub off stuck-on food--then rinse. The frying pan will still look and feel slightly greasy and that's OK. Heat the empty frying pan on the stove until every drop of water has evaporated. Let the pan cool slightly, then re-season with vegetable oil, wiping off the excess with a paper towel. After several uses and re-seasonings, the cast iron frying pan will develop a patina and become naturally non-stick. Proper seasoning after each use will maintain this patina.
Rejuvenate your frying pan if it has rusted. A cast iron frying pan left with water in it will form orange-brown rust spots. Scrub off the rust spots with steel wool and water, then re-season the pan as in Step 4. The rust does not hurt the frying pan but should be removed to prevent it from flaking into your foods.
You can purchase an ugly rusted cast iron frying pan at yard sales for next to nothing and easily rejuvenate it. Cooking with cast iron pans adds iron to your diet.
Do not leave your cast iron frying pan wet, as it will rust quickly. Never use dish soap as a regular cleaner for cast iron pans. Do not leave food sitting in your cast iron frying pan, as it will continue to absorb iron. Do not cook acidic foods (like tomatoes) in your cast iron cookware until it has been re-seasoned several times.