If a few dark or dull patches are still there, bring in baking soda. Keep a thin layer of water in the pan, sprinkle in some baking soda, and scrub with the cut side of a lemon. It may fizz a little, and that’s perfectly normal, because the acid and the baking soda are working together to lift stains. Note that lemon alone may not work on bluish, rainbow-like heat stains, so for those, a baking soda paste or a little diluted vinegar can do better.