For years I used Blacken-it from A-West for darkening metal details such as chain, wire, etc. The product is no longer available. I've also had some success with Hobby-Black, which I believe is also no longer available. I've seen posts on using NeoLube as a metal darkening agent, but my impression is that it is less permanent than the other two products, which actually etch the metal surface.
What do you use for this process, now that Blacken-it and Hobby-Black aren't around? Any suggestions would be appreciated.