A while back Og pointed me to this site with a home bluing formula/setup. At the bottom is a link to another, which has the formula I used. Having found the last ingredient needed, and having all the equipment, I gave it a try today. Here's the setup:
The burner is from Harbor Freight, cast-iron with two burner heads. The enamelware pot I picked up at a flea market, and the stainless pot(for the rinse) from a local store who has them cheap. They're both 16-quart. Not visible is the bottle of vinegar(in case of spill or splash), the heavy rubber gloves and the respirator(just in case). I set this up outside with a breeze blowing, no damned way I'd do it indoors unless I had some kind of fan or ventilation setup; might not be necessary, but I'd feel better.
I went with the second site's ingredients for two reasons. First, I couldn't find ammonium nitrate fertilizer that did not have sulphur added(Fed requirement, aftereffect of the OKC Bombing) and I didn't know how that might affect it. Second, the original site notes that his mix outgasses ammonia badly when you're mixing it, and the second avoids that.
I did have to order the nitrate of soda, as nobody around here carries it(hell, they'd never heard of it) and I thought I'd have to order the lye until I found it yesterday.
I got the two-burner rig so I could heat the rinse water along with the bath, so I lit the burner under the rinse pot while I mixed the ingredients in the other. I'd been afraid the stuff would have trouble dissolving in only a gallon of water, but no, the lye and then the nitrate went right into solution, just add no more than a cup at a time and keep stirring. I shut off the burner on the rinse water about the time the bath came up to heat. According to my thermometer(Wally World, bbq section, $5) by the time I had the nitrate dissolved the mess was already up to almost 200F, and it only took a few minutes to get it up to a rolling boil. It didn't start to actually boil until right at 250F, and with the slide, frame and some other parts in the burner on full kept it at a touch over 275.
I left the parts in for about 25 minutes, stuck them in the rinse and put the rest of the parts in(all hung on iron wire from a rod across the top of the pot). Everything came out a nice black except for the slide, which had an odd-colored section on the left front. It I scrubbed with a steel wool soap pad and washed off, then put back in for another 20 and it came out nicely. I've got everything coated in oil, and I'm going to let them sit until tomorrow before I reassemble. However...
I wanted to try this on a knife, so I took a dagger blade and treated it while giving the slide the second bath. The blade had a 400-grit finish, not mirror but very smooth and shiny
Please note that the tang was left with forge marks on the sides(the better for the epoxy to grab), and the tang is annealed to be easy to drill. I wrapped a wire around the tang so it held the blade horizontal; the solution was getting a bit low and it would not submerge completely if vertical. It got 20 minutes, then a good rinse, then oil. Now, these are not the best pictures, but they do give the idea:
The above was shot in the house. This one was shot outside so I could get the sun glinting on it:
I need to get a better shot, these just do not do the finish justice; it's not just dark, it's gleaming BLACK. The only contrast on it is that there's a bit of difference in the color between the hardened blade and annealed tang for some reason.
The pistol doesn't look like it'll be quite this marvelous, simply because it wasn't polished. I went over it and smoothed everything very nicely, but did no actual polishing. If this blade is any indication, if you do take the finish to (I'm guessing) a 240-grit or above, the result should be just as pretty as this blade.
Overall, this seems to work very well. It's supposed to be good for another 5 guns minimum, which makes it pretty cost-effective. I was going to use the knife to test out how well this finish wears, but it came out so damn pretty I hate to mess with it.
I had to use the wire it was hung on to hold the frame on its side; one gallon of solution in this size pot wouldn't let it submerge completely if you had it vertical.
Before putting the slide in for the second time I thought I'd add some water to bring the level back up from what had boiled off: Don't Do That, it is a Bad Thing. If I hadn't been standing well aside I WOULD have been spattered when the stuff spit. Wait until it's cooled off to add water.
It take the bath several hours to cool down, mine had sat for about two and it was still very warm when I put it in a plastic container for storage.
Do remember, lye will mess you up if you get careless with it.