Cast iron has acquired a reputation for being demanding. Most of that reputation is people repeating rules they have never tested.
Here is what is true.
Two different materials
Almost every argument about cast iron collapses once you separate the two kinds.
Enamelled cast iron is iron with a glass coating fused to it. It does not rust. It needs no seasoning. It is not reactive, so tomatoes and wine are fine. You wash it like any other pan. The enamel can chip if you knock it hard or drag metal across it.
Bare cast iron is raw metal. It rusts if left wet. It builds a polymerised oil layer — the seasoning — that becomes its non-stick surface. It is nearly indestructible and fully repairable.
Bread ovens and casseroles are usually enamelled. Grill pans and skillets are usually bare. Check which you have before following any advice, including this.
Seasoning, demystified
Seasoning is not a layer of oil sitting on the pan. It is oil that has been heated past its smoke point until it polymerises into a hard, slick, bonded film.
Which means: a greasy pan is not seasoned, it is greasy. And you cannot season a pan by oiling it and leaving it in a cupboard.
Most bare cast iron now arrives pre-seasoned and usable from the first day. Cooking on it improves it. Frying is more effective than any ritual.
The soap question
You can use soap. Modern washing-up liquid does not dissolve polymerised oil. The rule dates from when soap was lye-based and genuinely did strip it.
What damages seasoning is prolonged soaking, the dishwasher, and scrubbing back to bare metal.
The actual routine: hot water, a stiff brush, a little soap if it needs it. Dry immediately. Put it on a low flame for a minute to drive off the last moisture. Wipe a very thin film of oil over the cooking surface — thin enough that it looks dry.
That is ninety seconds.
Rust is not the end
Left wet overnight, bare cast iron will show orange. This is recoverable and always has been.
Scrub the rust off with steel wool. Wash, dry thoroughly, then re-season: a very thin coat of neutral oil, wiped until it appears dry, upside down in a 230°C oven for an hour, cooled in the oven. Repeat if you want a deeper layer.
A pan you can resurrect with an hour and some oil is not a fragile object.
Why bother at all
Thermal mass. Cast iron holds a great deal of heat and gives it up slowly.
Put cold steak into a thin pan and the pan temperature collapses, so the meat steams. Put it into preheated cast iron and the surface stays hot enough to sear. The same principle makes a bread cloche work, and makes a grill pan hold its ridges' heat under a dozen cold shrimp.
Nothing else in a domestic kitchen does this as cheaply.
The short rules
- Preheat properly. Cast iron is slow to warm and unforgiving if rushed.
- Never take it from fridge to hot oven, or hot pan to cold water.
- Dry bare iron immediately and oil it lightly.
- Do not cut on the enamel or stack it unpadded.
- Expect it to outlive you. Most of it does.