There are a numerous ways to blue gun metal, the oldest and probably the least expensive way is rust bluing.
The metal is prepped by removing old bluing, rust and any oil or grease. Then an acid solution is applied to the metal, the acid will accelerate the rusting. The metal is then placed in a humid environment to rust.
Some places (like Louisiana or perhaps Seattle in the spring) are plenty humid without help, but if you live in an area that is dry, you will want to build a "sweat box".
Disclaimer: If you chose to embark on the process, please use precaution, follow known safety rules and read the labels of any product you use.
Getting back to the chemicals, there are several brands on the market.
Plinkington's Classic American Rust Bluing Solution was very popular, but has been next to impossible to find for the last year or so (I just saw that Brownells has it in stock again).
It appears that Brownells has reverse engineered the product and are now selling a similar product.
There is also Mark Lee's Express Blue #1, Laurel Mountain Barrel Brown and a new solution simply called Rust Blue, sold exclusively at Rust Blue.com
The problem with all these solutions is that they never seem to be in stock and they are expensive. They range in price from 3.50/ounce to more than $15/ounce not including shipping charges.
Also some of these chemical solutions contain highly toxic elements.
So I did some research and came up with some recipes for home made bluing acids.
The one that looked the most promising includes 1 cup of Hydrogen Peroxide, 2 teaspoons of White Vinegar and one teaspoon of table salt. These are common ingredients available at almost any store.
You need to heat the Peroxide in the microwave for a few seconds, then dissolve the salt, then add the vinegar. The heat is supposed to help dissolve the salt. I used a mason jar to heat and mix the solution
The solution looks slightly cloudy, but otherwise colorless.
After mixing up the ingredients I put them in a container for storage. Make sure you mark it POISON so no one mistakes it for their beverage.
I am going to experiment on a piece of a shotgun barrel left over from another project (Zombies)
I know you are probably thinking I chose this barrel part because it has a vent rib. It is true that older shotguns with double barrels and vent ribs MUST be rust blued because the Hot Salts method contains caustic ingredients that will loosen the silver solder. The newer shotguns (like this Mossberg barrel) spot weld the ribs on, so they can be blued with any method. The real reason I chose this, is because it was the only piece of gun steel I had laying around.
First step is to remove the old bluing, I use naval jelly, it is cheap and easy to find. Wear gloves (especially if you have any cuts or open sores), if you are sensitive to chemical vapors you may want to wear a mask and make sure you have ventilation (outdoors or near an open window).
It works well, but it does leave a rough surface behind (it is an acid after all). So you need to clean that off with a wire wheel.
Next step is to sand/polish to the proper smoothness. I have read that the rust blue process will etch the metal with the acid solution and the rusting, so there is no point in sanding beyond a 320 grit finish. I decided to test that theory, I sanded one side of the barrel to a 220 grit finish and the other side to a 500 grit, we'll see if I can tell the difference.
Rust bluing usually provides a satin finish. If you are looking for a high polished blued finish, you need to use the Hot Salts method.
After sanding/polishing, put on some latex or nitrile gloves, you don't want to touch the bare metal with your hands from here on out.
Wash the metals with hot soap and water.
I used a dixie cup to hold a small amount of solution for soaking the cotton balls.
You want to soak the cotton ball, but not have it dripping liquid. Apply in one long stroke, try not to overlap your strokes and try to cover all the metal that needs to be blued. The bare metal immediately started to rust
My Dad built me this sweat box from old plywood he had laying around.
I didn't add a lightbulb and tray of water as it is springtime here in the Emerald City and the rain is coming down pretty good. I am guessing that the humidity in my unheated garage will be plenty to get the metal to rust.
If not I have a 100 watt incandescent (don't tell anyone) light bulb I can install in the base of the box with a tray of water, to create water vapor.
After just a few minutes you can see the rust forming.
After a week of sitting in the garage, this is what we got
It wasn't what I expected, I was hoping for a thicker coating of rust. I decided to boil it anyway and see what happens
After 10 minutes boiling in distilled water, the rust turned black
I used 0000 steel wool (de-greased in acetone) to card the surface, you get black powder that flakes off
I then started another round of rusting by applying my acid solution, rust immediately began to form.
Back into the garage for a few more days, I am going to add a pan of water and a light to help speed things up.
Here it is after a few more days in the garage
Another round of boiling
The rust again turns black
I swabbed more solution on and put it back in the box
Another round, The process is very slow.....but I guess that is why they call it Slow Rust Bluing...
It appears that I am not making much headway......I don't think my homemade solution is causing the rust to go deep enough. Time to buy some "off the shelf" stuff....stand by for part 2
As Mason Cooley once said that "if you call your failures experiments, you can put them in your resume as achievements!"