How to remove rust from metals without attacking the metal too much.
Use MSG like museums do all around the world.
Buy some monosodium glutamate (MSG) from your local Chinese store. Dissolve some in warm water. Soak your rusty item in it for three months or three weeks or a couple of years in the case of Captain Cook’s old anchor in Tahiti. If the solution looks too rusty, throw it out and start again.
The MSG dissolves the crusty rusty oxide but doesn’t have as much influence on the metal.
I’ve used it on rusty lawn edgers (the axle had swollen which prevented the wheel rotating), on a winch handle from our boat, on locks frozen in the sea air and on other stuff.
Museums have used giant vats of MSG to derust anchors and ship parts.
And you should know that MSG is fine to eat, despite the urban legends.
Joanna suffered from Chinese Restaurant Syndrome. She used to throw up exactly four hours after eating. It took us years to diagnose, but it turned out to be the popular wood-ear fungus (probably an Auricularia species). So, enjoy your MSG, but always ask for gluten-free water.