How do I care for a cast iron pan?
Cast iron is more forgiving than its reputation suggests, and most of the strict rules people repeat are unnecessary. What actually matters is keeping it dry and maintaining the seasoning.
Seasoning is polymerised oil bonded to the metal, not a coating that sits on top. It builds with use, and cooking with fat maintains it. This is why a well-used pan performs better than a new one and why simply cooking in it regularly is most of the maintenance.
Cleaning can include soap. The old prohibition dates from when soaps contained lye, which stripped seasoning; modern washing-up liquid does not. What genuinely damages seasoning is prolonged soaking, harsh scouring down to bare metal, and the dishwasher, which combines aggressive detergent with a long wet cycle.
The important step is drying immediately and thoroughly. Rust forms quickly on exposed iron, and a pan left to air dry will often show it by morning. Drying on a warm hob for a minute drives off residual moisture better than a towel alone. Wiping a very thin film of oil over the warm surface afterwards protects it; the film should be almost invisible, because excess oil becomes sticky rather than hardening.
Rust is repairable rather than fatal. Scrub it off, wash, dry and re-season by wiping a thin layer of high smoke point oil over the whole pan and heating it in an oven above the oil smoke point for an hour. Several thin coats beat one thick one.
The genuine limitations are worth knowing: prolonged cooking of acidic foods such as tomato sauce will strip seasoning and impart a metallic taste, and the pan retains heat far longer than you expect.