Originally Posted by oneclick

OK, here's the list of common methods and their characteristics:

Vinegar (ph ~3) - not much effect of either rust or steel, pretty much harmless to humans
Citric acid (ph ~2.5) - will remove rust slowly, wont do much to steel, similarly harmless
Oxalic acid (ph ~1.3) - will remove rust, slowly but faster than citric acid, won't do much to steel. Wash it off if it splashes on you and don't drink it.
Evapo rust (ph ~6) - will remove rust, slowly but faster than citric acid, won't do much to steel. Supposedly harmless but they don't say what's in it.
Phosphoric acid (ph ~1.5) - removes rust, faster than evaporust, won't do much to steel. Wash it off if it splashes on you and don't drink it.
Tannic acid (ph ~6) - will remove rust fast, leaves steel black on the surface which will brush off. Wash it off if it splashes on you and don't drink it.
Hydrochloric acid (ph ~1) will remove rust FAST, will remove steel FAST, will remove skin FAST. Don't even think of using this stuff.
Electrolysis - removes rust completely, leaves steel alone, safe except for low-voltage electricity and possibly whatever you use for an electrolyte; washing sode is ph ~11 and thus caustic, but you don't use much even of that in a huge volume of water.

The method I use depends more on the size of the part and the amount of rust. Small bits - nuts,screws,etcetera - go in a plastic tub with enough phosphoric axid or oxalic acid to cover them, and taken out when done (a few hours). Large things rusty all over usually electrolysis, especially if very large - did a Vespa frame a while ago and that much oxalic acid would have cost more than the moped did. Bike frames only oxalic acid because they have brazed joints and I'd have to find out what electrolysis will do to one before even trying it.