I’ve always used white vinegar boosted with glacial acetic acid. Works pretty quick. In fact keep an eye on it or it’ll keep eat’n away. It’s been awhile, but I wanna say a 10” pan will be shiny in about 4-6 hours with a brush’n now and then. In a black tub out in the sun helps speed it up. I clean my smith’n tongs up now and then when they get rusty by dropping them in a pvc tube full of that solution.