Rubbing alcohol and gun blue, people; it's all rubbing alcohol and gun blue
No, don't mix them together (God knows what will happen, and we probably don't want to.....); clean with alcohol; darken with blueing. This tends to give brass etc. a dark brown colour, and will not always match existing patinas. Go to a student college bookstore (or maybe a library, but a college bookstore at class-starting time........online I'm sure you could find these, too), and go to the Fine Art section; there you will find metalworking books and in at least some of them tables and listings of reagents for patinating various metals in various colours; just so's you know; but, yeah; gun blue will affect many metals, and the coating it leaves is usually fairly easy to remove (BTW, in reference to a question about its affects on chrome I did some tests on chrome plated stuff I have, and if you act within a minute or so of application, the dark wipes right off; I think it hardens more over time though, especially if you leave the wetness 'til it dries down; at first when you put it on nothing will happen, but then it begins to darken; I use a paintbrush or rag, and "working it in" with a sort or rubbing/scrubby motion seems to help things along, or at least to occupy the monkey while it waits
