i've used oxalic acid with good results, i think it can be bought from ebay in granule form. works out far cheaper than coke. you only need to add a small amount to the water. i've also used brasso on my mongoose nickle forks which had pitting on them.
Having tried the coke and tinfoil and the oxalic acid I will never use anything but the acid from now on. No matter how careful you are the tinfoil is leaving tiny scratches.
The acid does the job much better. I did a frame recently and all i did was bath it in the acid mix in a plastic bin for 24 hours and during that time a quick brush round the rusty areas with an old toothbrush.
Came up mint without hours of scrubbing
Get it cheap in granular form off ebay.