So I thought I would have my wife take pictures of my bluing process so I may explain it step by step.
Step one: Prepare the steel. The first thing you need to know is that only steel or iron can be blued. The process will add a black oxide finish to your gun, this oxide finish is rust, that heat has converted from red to black.
The second thing you need to know is that the steel must be clean and free of ALL oils. This includes the oils from your skin. The third thing you need to know about bluing is that the condition of the steel before bluing will affect the condition of the finish after bluing. Bluing will not hide pitting or surface imperfections. Because it is black, some of the imperfections may not be as noticeable, but it will not "fill" voids or scratches.
Here are the guns prepped. I have polished the steel to the desired level of shine and cleaned them with Acetone to remove oils and residual buffing compound.
I blue guns outside, for a number of reasons, not the least of which is that the chemicals are very harsh on wood and metals, so it is best to perform this under a large vent hood or outdoors at least ten feet away from any vehicles or structures.
I set it up like an assembly line. Clean the parts in soap and water, prepare for the salts bath, the crab pot cooker is the rinse bath and then the parts move to cold water rinse and high pressure air before being dunked in the oil bath
It is very important that you follow safety guidelines. Bluing solution is caustic and very hot, they can cause heat and chemical burns. Keep a running hose ready as well as baking soda to neutralize the acid.
You want to wear long pants and long sleeve shirt, get a full face shield, a vinyl apron and "gauntlet" style gloves that go past the elbow.
If you get hurt doing this, don't blame me, I warned you!
You will also want to have plenty of nitrile gloves and shop rags handy
Here is my bluing tank, it is made from cold rolled 3/16" steel, 40" x 6" x 6", the burner on the bottom is from a BBQ grill. Notice the Candy Thermometer, it goes to 400 degrees....
The bluing salts can be purchased from suppliers like Brownells or Dulite, but I found that it is cheaper to make your own.
The chemicals needed include Sodium Hydroxide, this is also known as Lye.
Lye is used for drain cleaners, soap making, treating sewage, bluing guns and as a food additive....
You can get it as a drain cleaner (make sure it says 100% lye, as some formulas contain aluminum...not good). I get mine from a place called the Essential Depot. This is food grade, the highest quality.
The second ingredient is Sodium Nitrate, this is a food preservative (used in hot dogs and sausages) and fertilizer, it can be found at home & garden stores or at pottery supply houses. I got mine from a local pottery supply store, I buy in bulk & save mucho quatloos....
The 3rd chemical is Di-hydrogen monoxide, also known as water.
I used to use distilled water, but have since switched to making my own filtered water using a Zero Water filter
Add the dry chemicals to the tank, 2 parts Lye to 1 part Sodium Nitrate, in this case I used 10 pounds of Lye and 5 pounds of Nitrate + 1 gallon of water to start.
I like to "layer" the two ingredients, so 2 pounds lye, 1 pound nitrate and so on....water comes last
Better suit up (I know I wasn't wearing my PPE here) trust me you want to be careful, once water hits the mix, the chemicals become volatile for a bit and give off some heat and some gases.
Then fire up the burner and get the tank heated up. My wife snapped the picture just as the propane ignited.....remember be careful!
While the salt bath is heating to 275 degrees, I wash the gun parts in dish soap and water. Do not use your tooth brush......use someone else's :) ...and wear latex or nitrile gloves, you don't want your skin coming in contact with the parts at this stage.
Here is my small parts basket, notice the nice blued finish..
For the really small parts use some safety wire to connect them so they don't fall through the holes in the basket.
I also run the wire through the barrels of the guns to allow me to position them correctly in the bath. The question often comes up about plugging the barrels. You DO NOT want to plug the barrels. The air will heat up and spit out the plugs causing a minor explosion sending hot & caustic salts airborne. The bluing will not hurt the bore, even if it is chrome lined....no worries.
Wear your protective safety gear anytime you approach the salt bath....
After 20 minutes or so, check on the parts, if they are a deep black color, they are done, move them to the boiling rinse tank.
After a good soak and some plunging (to remove the salts from any nooks and crannies. Move the parts to a cold water rinse, this time I just used my garden hose, sometimes I use a 5 gallon bucket filled with clean, cold water.
After the cold water rinse, blow off the water using an air compressor. This helps keep the oil tank from getting contaminated with water.
Next move the parts to the oil tank. I use a garden planter that is 30" x 8" x 6", filled with WD-40 ( you can see it in the pic above).
Brownells and others sell special "water displacing oil", but the if you didn't know the WD in WD-40 stands for water displacing and it is easier and cheaper that the specialty stuff. You can probably use any oil, but I would read the labels and make sure there is no weird ingredients that could harm your new finish.
Note, sometimes you will get a red or black "soot" on the surface of the parts, use plenty of oil and 0000 steel wool to rub it off, you should have nice shiny black steel underneath. If not, simply clean the parts with soap and water and start over. I do not turn off the heat until all the parts have been inspected, just in case there was a problem and I need to return them to the salts bath.
Here are the parts after removing from the oil tank. I will spray them with some Remoil and let them sit overnight before handling/reassembly.
The last step is the clean up. You should NEVER put the spent salts down a storm drain. They are not so harmful to dump down the sewer as the chemicals are used for drain cleaner and for sewage treatment, however, I would consult my local water department first (although they probably will not understand chemistry and what your solution is/does). The best method is to save them, if the solution has not been contaminated, you can re-use it as many times as you need.
If disposal is needed your best bet is to find a chemical disposal facility, these people will understand what you have.