A cast-iron skillet is a heavy pan that holds heat and lasts for decades if you keep it dry and thinly oiled. It is not a fragile antique and it is not a self-cleaning miracle. The black surface people call seasoning is oil that has bonded to the metal through heat. You maintain it by washing off food, drying the pan completely, and wiping on a film of oil so thin you can barely see it. Most problems that look like failure are thick oil, leftover moisture, or heat high enough to burn the coating off.
New skillets sometimes arrive with a waxy factory coating. Wash that off with warm water and a little soap before you cook. Dry the pan, then give it a proper seasoning if the maker did not already leave you with a dark, even surface. After that, ordinary cooking does most of the maintenance. Bacon, frying, and other fatty jobs help. Long boils of very acidic food on a brand-new seasoning can strip it. A well-used pan can handle a tomato sauce for a normal dinner. It should not be your pot for an all-day simmer of tomatoes until the seasoning is mature.
Wash it like a pan you intend to use again
Wash the skillet while it is still warm, not screaming hot and not three days later. Hot water and a brush or a non-scratch scrubber remove most food. A small amount of dish soap is fine. Soap will not destroy a real seasoning. What damages the pan is soaking it in the sink overnight, running it through the dishwasher, or scrubbing it with a harsh oven cleaner. If something is stuck, simmer a little water in the pan for a few minutes, then scrape with a spatula. Do not take a cold pan from the fridge and blast it, and do not plunge a ripping-hot pan into cold water. The shock can crack iron. Let a very hot pan cool for a few minutes first.
Skip the advice that says never to wash cast iron. Old food and rancid oil are not seasoning. They are dirt, and they make the next meal taste like the last one in the worst way. Rinse until the water runs clear. Feel the surface. It should be smooth, not greasy with chunks. If a thin layer of seasoning comes off after a harsh cook, the pan may look patchy. That is repairable. Rust is repairable too. Neglect is the only real threat.
Dry the pan immediately. Water left in the iron will rust it, sometimes by the next morning. Set the skillet on a burner over low heat for two or three minutes until every drop is gone, including the droplets hiding near the handle and along the pouring lips. A towel dry is a start. The burner is the finish. This step looks fussy the first week and then becomes automatic. It is the whole reason some people think cast iron is difficult. They stopped before the drying.
Oil it thinly or not at all
When the pan is dry and still warm, put a few drops of neutral oil on the cooking surface. Wipe it with a cloth or a paper towel until the pan looks almost dry again. If the towel picks up wet oil in streaks, you still have too much. A thick coat turns sticky and collects dust. A thin coat protects. You do not need to oil the pan after every single use once the seasoning is strong and the pan is stored in a dry place, but oiling after washing is a cheap habit that prevents rust. Wipe the outside occasionally too, especially if you see dull orange specks starting.
Use a neutral oil with a reasonably high smoke point for maintenance, such as grapeseed, canola, or another plain vegetable oil. You do not need an expensive bottle. Do not pour the oil and walk away while the burner is still on. A forgotten oiled pan over high heat will smoke hard and can burn the seasoning. Low heat for drying, a wipe of oil, and then off. If the kitchen fills with smoke, the heat was too high or the oil was too thick. Ventilate, let the pan cool, and wipe it again.
Sticky, gummy patches mean oil sat on the surface and never got hot enough to set, or it was applied in a heavy coat. Warm the pan, scrub the gumminess with hot water and a stiff brush, dry it, and start over with a thinner coat. Flaking black chips after a long storage often mean an old thick layer is letting go. Scrub loose flakes, dry, and cook. The pan underneath is still a pan. People throw away skillets that needed a scrub and a Saturday of ordinary cooking.
Heat it with a little patience
Cast iron holds heat so well that a high burner is usually more than you need. Preheat over medium for three to five minutes before you add food. The pan should be hot across the base, not only in a circle the size of the flame. Add oil when the pan is hot if you are searing, then add the food. Food stuck to a cold pan is why people think they need more oil than a small lake. Preheating prevents more sticking than any gadget.
The handle gets as hot as the pan. Treat it as hot even if you are used to pans with a plastic grip. Use a dry towel or a mitt. Do not grab it on the way to the oven. Cast iron can go from stovetop to oven, which is one of its best traits, and the entire object including the handle will be at oven temperature when it comes out. Set it on a heatproof surface. Do not set a hot skillet on a glass cooktop if the maker of the cooktop forbids heavy iron, and do not drop it. The pan can crack a glass top or a tile, and it can break a toe. Slide it, do not toss it.
For eggs and other sticky foods, wait until the seasoning is decent and the pan is properly preheated. Use enough fat. A brand-new skillet may stick a little for the first weeks. Keep cooking. Each fatty meal improves the surface. Do not sand the pan down every time an egg clings. Scrape, wash, dry, oil lightly, and try again tomorrow.
Season it when the surface needs help
If the pan is new, stripped, or rusted, give it a deliberate seasoning. Scrub rust with steel wool or a stiff brush until the orange is gone and you are back to bare gray metal. Wash, then dry on the burner until the pan is fully hot and moisture-free. Rub on a very thin coat of oil, inside and out, then wipe it off as if you changed your mind. The pan should look barely oiled. Place it upside down on a rack in an oven preheated to 450 degrees Fahrenheit, with a sheet of foil on the rack below to catch drips. Bake for one hour. Turn the oven off and let the pan cool inside. The kitchen will smell like hot oil. Open a window.
One round helps. Two or three rounds, each with a fresh thin coat, build a smoother surface. More oil per round does not speed this up. It makes a sticky shell. After the last round, cook something fatty at a moderate temperature. You do not need to baby the pan with a special ritual every week if you dry it and use it. Seasoning deepens with ordinary dinners.
Store the skillet in a dry cupboard. If you stack pans, put a paper towel or a cloth between them so the surfaces do not rub and so any trapped moisture has a place to go. Do not put the skillet away wet. Do not store it in the oven if you preheat the oven without looking, unless that is a habit you trust completely. A forgotten skillet in a heating oven is a smoke alarm waiting to happen. Hanging the pan on a wall is fine if the hook is strong. Cast iron is heavier than it looks when you are half asleep.
Mistakes that rust or ruin the surface
Soaking the pan is the fastest path to rust. Leaving food in it overnight is the second. Air-drying it in a dish rack is the third. A dishwasher cycle is the fourth. The fifth is oiling it like you are varnishing a deck and then storing it. The sixth is heating an empty pan on high until the seasoning turns ashy gray. Medium heat cooks almost everything you will make in this skillet. Save the highest heat for a short sear once you know the pan, and do not walk away.
If rust appears, it is not a tragedy. Scrub it off, wash, dry on heat, and season. If a tomato sauce stripped a young seasoning, wash, dry, and cook a fatty meal or repeat the oven step. If food tastes metallic, the pan may be bare in spots or poorly dried and starting to rust. Look at it in the light. A healthy surface is dark and fairly even, and a drop of water beads or skims rather than soaking in like a sponge. You do not need a perfect mirror. You need a dry pan with a thin film of oil and a habit of using it. Cook in it several times a week, wash it, dry it on the burner, and it will outlast the rest of the kitchen tools you own.