Here is a simple formula, and it wont kill ya, well at least it hasn't me yet.
Mix up a batch of the following, half hydrogen peroxide (drugstore grade is fine), half vinegar, and a pinch of salt. The reaction is pretty fast, and seems to produce a gas of some sort (I'm going to guess hydrogen) Just put it in a pump spray bottle and spray on bare metal. Works faster if the metal is clean and degreased first, either a wax & grease remover or simple paint thinner works great to remove any grease. The rust seems to form as the solution dries so it works better/faster in warm dry weather. I've even used a hair drier to speed it up when its cool, humid, or I'm just real impatient. The quick 5 min rust is fairly light but a little spray of clear coat will seat it in, but I usually like to spray the mix on and then set it outside in the sun for a few days and the rust sets in deeper on it own.