An old time method to blacken steel parts: gather berries from the Sumac plant, wrap them in cheesecloth and then put into a kettle of boiling water. Cook for a bit, then put in the parts to blacken- remove when satisfied with the color.
To "age" brass hardware, degrease the component with lacquer thinner and use gun blue, available from any sporting goods store. It's cheap, the results are instantaneous, and it works well on nonferrous and some plated ferrous metals, and is safe to use. Finish the effect by stropping with steel wool to affect "wear" spots, and spray with a clear flat lacquer.