This is done only prior to the first seasoning, or before starting from scratch if your seasoning gets abused beyond hope. Most new cast iron cookware comes preseasoned but I recommend seasoning them as well.Start by washing in hot soapy water (this is the only time you will ever use soap on your cast iron), rinse it well, and put it upside down in the oven, set to 200 degrees or less, to dry completely. If your pan is now a dull gray all over, you can move onto the actual seasoning process. If there are patches of rust or baked on gunk, grab some steel wool or a wire brush. For really stubborn greasy residues, try covering them with a natural oven cleaner and put it to work for you.
Seasoning Your Cast Iron
There are so many ways to correctly season cast iron cookware. This is what I recommend and prefer. Apply a very, very thin coating of an edible fat or oil (grass-fed lard, olive oil, or even duck fat) to all surfaces of the item, including the underside, handle, and sides of the pan. Wipe off any excess, then bake it in a moderate (300- to 350-degree) oven for a few hours, allow it to cool, and repeat a few times until it starts to turn an even or speckled brown.
As you continue to use your cast iron, it will darken and become an even, shiny black, which means it’s getting really well seasoned and naturally nonstick. Using a stainless steel spatula with a straight edge and curved corners as you cook will help polish the inside surface, making it even smoother and more nonstick.
Do not leave food, especially acidic foods like tomatoes, in your cast iron for more than a short time after cooking. It will react with the iron, making it black and terrible tasting, and ruin your seasoned cookware. It’s actually a good idea to avoid cooking acidic foods in cast iron at all or at least until you develop a good seasoning.
Soap or detergents should never be used to clean your cast iron cookware but here are a few tricks to make cleanup easier. Immediately after use, hold your pan under running hot water and give it a quick swish with a nylon or natural-fiber brush; don’t use steel wool or metal scrubbies. Use a nylon or wooden scraper to dislodge small stuck-on bits. If there is lots of stuck-on food, sprinkle some salt (kosher salt works well because the grains are so large) on the pan then go at it again with your brush. You can also fill the pan with hot water and return it to the stove on low heat for a minute or two to loosen food bits, then repeat the hot-water-and-brushing treatment. Return your cleaned pan to the stove, turn on the burner, and allow it to dry completely. If there are any dull gray areas, coat the pan lightly with oil or fat before putting it away.