Guys,
The B.P. residue method is the way I darken shiny brass to give it the old looking patina. Here is how I use this process. I bring the shiny brass gun to the shooting range. I shoot the gun and swab the bore with a spit patch. Then immediately I begin to wipe down the shiny brass with the dirty, wet patch. It darkens the brass nice and quickly, and the right color, too. If you collect the dirty patches in a bag to take them home for later use, it will not work as well as a really fresh dirty patch, they must be really fresh. If you keep the dirty patches in a plastic bag in the shop for a long time, then try to use them, they don't work at all.
Also, commercial cold blue solution will work, it gives a too black color (in my opinion).
Jim