I did get a real good rust blue from ( the old recipe) of Birchwood Casey's plum brown. It was an accident. I was a newbie, building my first kit gun, and was told the only way to stop the rusting for sure, was to use boiling water to rinse the barrel. I soldered up the ends of a metal chicken feeder, and put it over two eyes of the kitchen stove, with distilled water in it. Just as I put the barrel into the boiling water, the phone range. When I got back to the barrel it was as black as night. I removed it, and carded it off, as was pleased with the light blue finish that was left. So, I repeated the process several times until I got the color I wanted. I shot the gun for years, and eventually upgraded to a custom built gun. I kept that rifle for a loaner for several years, and eventually traded it for an aluminum canoe. That blueing never showed any wear. It did start to turn a little brown in the recesses but never wore off.
Hungry Horse