Vinegar and a scrub pad.

Vinegar.

Mix equal parts white vinegar and water, submerge the rusted pan, and let it soak for about an hour – check every 20 minutes. The rust will lift. Scrub it off with a stainless steel scrubber or chainmail (both are fine for cast iron, despite what the purists say). Rinse thoroughly, dry immediately, and re-season.

Abrasive methods like sanding or wire wheels work, but they’re overkill for light to moderate rust and they might leave scratches that make seasoning stick unevenly later. Electrolysis is the gold standard if you’re restoring a museum piece, but for a kitchen pan you just need to use tomorrow? Vinegar soak is faster and zero setup.

Don’t let it soak overnight. The acid will start etching the iron itself. An hour is plenty. After you scrub, dry it on the stove – heat it until water evaporates on contact – then apply a thin layer of oil and bake.

If the pan is pitted with deep rust, that’s a different conversation. But for surface rust that came from leaving it wet? Vinegar. Always.