When we moved into our new very old house it was a mess, or should I say before we moved in. I cleaned for weeks before we moved one box in because the previous occupants had been total pigs! One of the great features of the house is an old fashioned claw-foot tub (number 5 on bucket list!). But it was full of stains of some kind, probably rust. I tried the harsh store bought, guaranteed to remove it or your money back stuff that put tons of fumes into the air. It didn't do much.
Then I remembered in a book I have called something like 1001 uses for common household items that it had said salt and lemon juice removes rust stains from tubs and sinks. Well I had both and thought what the heck and tried it. I can say not only did it work like a charm, way better than the store bought stuff, but it also didn't put tons of nasty fumes into the air. Instead a nice lemon scent. I love it when old fashioned cleaners work better than the new harsh chemical stuff!
I am adding how I did it! Sorry everyone I completely blanked out to do this lol!
So what I did was first wet the area with lemon juice so the salt would stick better, then sprinkle the salt on, then re-wet with more lemon juice. I let it sit for a minute or two then scrubbed with a washcloth if the stain is still there. Some stains just disappeared, but the ones that were very severe had to be treated two or three times before they came off.