Cast iron pans are seasoned by applying a thin layer of oil or shortening to the entire pan, then baking in an oven preheated to 325 degrees Fahrenheit for one hour. The pan should be placed upside down on the oven rack with aluminum foil on the rack below.
The non-stick layer created by seasoning a cast iron pan is called patina. Patina is created when the layer of fat oxidizes and bonds together to create a shiny, hard surface on the pan. Flaxseed oil is an ideal oil to use for seasoning because it creates the best patina. Once the pan has cooled down, the seasoning process can be repeated several times after the initial seasoning to enable multiple layers of patina to form.
A seasoned cast iron pan should only be washed using water. Using a small amount of mild dish detergent is optional. The pan must be dried immediately after washing to preserve the shiny, non-stick cooking surface that seasoning creates. Using a clean paper towel, apply a thin layer of oil after each use to preserve the patina. Store the seasoned pan with a clean paper towel between it and other pans to avoid damage. The appearance of dullness or rust indicates that the pan requires seasoning.