Hot dog! I can rust blue!
I tried an experiment today to see if I could do it. I tried once before some years ago, and got a nice blue-black color, but a muddy brown underneath it when in the sunlight. Well, I tried it again.
I did this triggerguard. Just the bow and grip rail section. Wasn't worried about the rest. I polished it about as close to mirror bright as I cared to. Brought out the old bottle of Herter's Belgian Blue. I got a pot boiling with some pure water. I would heat the part with a torch, hot enough so that when I applied the stuff, it evaporated off real quick. I put the stuff on, rubbing it on quite a bit, then I put it in the boiling water for a few minutes. Took it out, rubbed off what little rust was on it with steel wool, and repeated. Over, and over, and over. I don't know how many times I did the cycle. Several. Probably more than was necessary, but I wanted to be sure. I was actually worried that the more I got on, the harder it would be to get rid of the brown color, but actually, the more I put on, the better it looked, and the more the brown went away.
What I ended up with is this deep, satin dark blue-gray, which is exactly the finish I have been told that rust blueing is supposed to produce. I'm not sure, but I don't think it's possible to make a mirror bright blue like a modern hot blue. The stuff etches the surface of the metal, and you have a satin, "micro-crystalline" surface. And, best of all, I have ZERO brown color left! None whatsoever. Not in any kind of light. No muddy brown. I'm happy.
I think this will make a durable finish, which it is widely reported to be. I was scrubbing it down with steel wool, and it wasn't wearing the blue off the corners or anything, so it seems pretty tough.
My first real project with this is going to be my S&W M22-4. It has been "delocked" (if you are familiar with the current infernal lock system, you know what I mean) and the holes filled, the slot beside the hammer has a slip of steel soldered in place. Supposedly, they MIGHT melt off the solder if someone tries to hot-blue it, so rust blueing is the "safe" alternative. (I can't imagine that they get it hot enough to melt tin, but that's what they say...)
I am convinced that rust blueing was done in the 18th century, but am unable to prove it. I've seen 18th century locks and mounts that SEEM to be rust blued, but can't say for sure.
I have a barrel blueing tank (48" long) that I can do barrels in. I guess the best way for me to heat it is to build a long wood fire under it.
I'm ready, I'm ready, I'm ready....