How do you season and care for cast iron?

Seasoning is not oil sitting on the surface; it is oil that has been heated past its smoke point until it polymerizes into a hard, plastic-like layer bonded to the iron. Building it means applying a very thin coat of a neutral high-smoke-point oil, wiping the pan until it looks almost dry, and heating it upside down in an oven above the oil's smoke point for an hour, then repeating several times. The most common error is applying too much oil, which produces a sticky, uneven surface rather than a hard one.

The soap prohibition is largely obsolete. It originated when dish soaps were lye-based and genuinely aggressive; modern detergents do not dissolve polymerized seasoning, and manufacturers including Lodge now explicitly say soap is fine. What does damage cast iron is water: prolonged soaking, running it through a dishwasher, and putting it away damp, all of which cause rust. The routine that works is washing promptly with hot water and a brush or mild soap, drying immediately and thoroughly, ideally on a warm burner for a minute, then wiping a very light film of oil over the cooking surface before storing.

Two further points. Acidic foods, tomato sauces, wine reductions, citrus, can strip seasoning during long cooks, which is a matter of degree rather than prohibition: a quick pan sauce is fine, a two-hour simmer is not. And rust is not fatal. A rusted or badly damaged pan can be stripped back to bare metal with steel wool, oven cleaner, or electrolysis and reseasoned completely, which is why century-old pans remain in service. Carbon steel behaves similarly with less mass and faster response, and enameled cast iron requires none of this since the enamel is the surface, though it should not be heated empty and chips permanently.