Caring for and Cleaning It
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 spaghetti sauce, in your cast iron for more than a short time after cooking. It will react with the iron, making it black and icky tasting, and ruin your carefully developed seasoning. It's actually a good idea to avoid cooking acidic foods in cast iron at all until you develop that nice shiny, black surface.
Cleaning cast iron can seem tricky, since you shouldn't use soap or detergents (or put it in the dishwasher), 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.
Store your pan uncovered in a dry place to prevent rust. I store mine upside down in my oven, which has a pilot light so it stays dry and faintly warm even in our humid summers—and I almost always remember to take it out before I turn the oven on to cook in it.