Re: Jim Keenan's comments about cold bluing wearing off quickly.
George Stringer first recommended Ox-pho Blue to me several years ago, and I've found that it is substantially better than other cold blues.
I took an old shooter Luger that was in pretty sad shape, stripped it down to white, and redid it with Ox-pho Blue. I'd defy you to tell it from an older Luger's factory blue (I had one of those too, and they were almost indistinquishable.) And it has proved to be as durable as factory bluing. But I put a LOT of thin coats on.
That has NOT been my experience with other brands of cold bluing -- which were, at best temporary recoloring.
Surface preparation is critical, and George suggested applying it in very thin applications, with almost-dry cotton balls. (I used cleaning patches.)
Worked for me.