Iron is subject to several kinds of oxydations. The rust [Fe2O3], is the naughty one, because it is formed by irregular crystals which grow (they use more space than actual iron). But other kinds of oxydation may form a regular and hard coat of protection.
Below feature two easy ways of getting rid of rust adapted to nose flutes.
I have a vintage Humanatone which was just lightly rusted, and I wanted to clean it and protect it from future attacks. I didn't want to change much its color, just to fix it in a stable state.
An easy trick for that is to dip the thing in phosphoric acid. This acid transforms the rust Fe2O3 into iron phosphate FePO4, which forms a stable protective coat. OK, but where to get phosphoric acid ? So easy! Coca-cola!
So, I opened a bottle of Coke with a Pfaff Nasenpfeife (High-tech german nose flute which includes a bottle opener (!)), and let my Humanatone dabbling for a night in its Coke bath (yuk!).
Next day, I rinsed the flute (don't drink the Coke!!!) in water added with baking soda (to stop acidic action) and, brushing with a piece of very soft steel wool (000), I got the shiny back. I just sprayed some lubricant (WD40 or so) all over the nose flute (inside included) and wiped it with a paper towel.
More, with the action of phosphoric acid, the different alloy layers had appeared, as if my flute had been forged with Damascus steel!
Another nose flute I have got was seriously rusted when I got it, really attacked, and the method explained above would not have been efficient enough. So, I tried the hard way.
The hard way requires more products, but gives an incredible result. It consists in blueing the flute, exactly as one would do with a gun barrel. That is applying a special oxydizer ("Gun Blue") which will form a very hard black oxyde (magnetite Fe3O4) protective (and beautiful) coat.
First, I performed the Coke bath trick, and the next day removed all the oxyde with a Dremel drill mounted with a polishing disk (plus red paste), then by sanding with very soft steel wool (000) (pic 1). I sprayed some grease remover, wiped the flute with paper towel, and avoided to touch it with my fingers anymore (pic 2). I put some Gun Blue in a (clean:) cat food tin (pic 3).
In conclusion : two methods, the light one and the heavy one, for two very different results. Please feel free to ask questions if something is unclear.