Ok, so most people have heard about or used rust bluing before right?
Basically, you swab the object with an acid mix bought from midwayusa or brownells, put the part in a sweat box, boil it to deactivate the acid, card off the rust, and repeat the process up to 8 times to get full coverage. 8 days to finish optimally.
Most smiths don't do this any more because it's just too time consuming and most people are cheap and don't want to pay for the labor involved. Also, if you apply the finish unevenly, you will get streaking that takes even more applications to blend in.
Here's something I've been experimenting with that I'd like to share with the community at large:
If you haven't seen electrolytic rust removal before, just type it into youtube and watch a video. Pretty simple. A battery charger, a sacrificial anode, some baking soda and some water. All these aim to get rid of rust, leaving it all on the sacrificial anode.
What we want to do is create rust! (black oxide)
All you do is reverse the current. Put the positive lead on your part that needs bluing, put the negative lead on something that is rusty.
After a couple hours, turn off the electricity and remove your part. It should have a nice surface layer of rust on it. Underneath that surface is black oxide.
Using a carding wheel (recommended) or some 0000 steel wool, start lightly polishing the red rust off. Keep putting it back in the tank, rusting, and carding until the entire surface is covered in black oxide. Because we are using baking soda, just rinse it off in the sink. You don't have to boil the part to remove any acids, like with the bluing solutions out there.
The electrolysis only works in a straight line between the anode and cathode, so you will need to rotate your part as it gets covered. As soon as you get adequate coverage, and you're happy with the finish, put the part in a solution of ATF/WD-40 to displace the water and halt any future rusting.
WARNING: Try this on some tools in your garage before anything gun related. If a part is extremely thin, like a knife blade you will eventually rust the sharp edge off of it and it will need resharpening. Rusting still causes a part to lose some of it's mass, so I would highly recommend only using this on larger parts. In a nutshell, don't use it on small internal gun parts.
2nd WARNING: See those little bubbles rising to the surface of your water? That's hydrogen! The byproduct of putting an electrical current thru water to convert/remove rust creates hydrogen. Don't smoke or do this around open flames or sparks. If you do this indoors, open a window or turn a fan on to disperse the gas that rises from your container, or if you're like me, open your garage door.
Because this doesn't involve the use of acids, expensive solutions, or long wait times, I believe that you can get pretty proficient in this technique in a short time. It's so simple, I'm sure some gunsmiths have figured it out on their own, but don't want to give their competitors an edge. I KNOW I'm not the only person to figure this out.
It took me about 8 hours to complete covering a large high carbon knife blade in black oxide (Instead of 8 days.) There was a little pitting on the back of the blade that I didn't like, so I ground off the pitting and it's back in the solution as I type this. (I think the pitting was because I never bothered to card that part off the knife off, so it accelerated the rusting.)
The finish looks like what you see on drill bits. It's a non glare, dark grey finish (almost black) that doesn't reflect light and holds oil just like parkerizing. I believe that the higher the carbon content, the faster you'll see results. If there is high nickel or chromium content, your part might not rust like you want it to, and it might be a better cantidate for hot salt bluing or using a harsher solution than baking soda.
I believe that information like this is too good to keep a secret, and there are countless guns that won't ever get refinished because it's too expensive to do for most folks, so my motivation is to help out everyone by sharing this. That's how society improves. The free exchange of information.
Now go have fun experimenting and save your rusty tools!
Andy.