Heat is the secret

Don’t air-dry it. That’s how you get flash rust. You have to dry it immediately and thoroughly.

After washing with mild soap and water (yes, soap is fine for modern seasoning), rinse well. Then put the pan on a burner over medium-low heat for a minute or two until all the water has evaporated. You’ll see the water sizzle and steam off. Once it’s fully dry, turn off the heat and let it cool enough to handle.

If you want to be extra careful, rub a tiny drop of oil onto the warm surface before storing. That seals the iron against moisture in the air. A paper towel with a smear of vegetable oil is all you need—don’t go heavy or it’ll get sticky.

One more thing: don’t ever leave a cast iron pan to drip dry in a rack. It’ll rust before your eyes. Heat drying is the only way that works.