One of the most common questions gunsmiths like me get asked is "how do you blue a gun".
I covered this topic nearly 10 years ago and decided to update it as my equipment and methods have evolved a bit.
To start with we need to explain the science, then I will show you how I do it.
For starters most guns are made of steel, steel is an alloy of iron and a small amount of carbon (usually less than 1%).
Modern gun steels often have other metals in the alloy like chromium or nickel. These alloys can affect the way the guns are blued.
Bluing is not really the correct term, the finish is actually black oxide.
We all know what happens to iron or steel if left unprotected, it rusts, more precisely it oxidizes. Oxygen attaches itself to the metal and creates a new alloy: Iron oxide. Iron Oxide has a reddish orange color.
When you heat iron or steel that has been oxidized, it changes the color and composition of the oxide to a hard black surface. This black oxide surface is called bluing in the gun world, everywhere else it is called black oxide.
Just a reminder, you can only blue steel or iron. Aluminum will oxidize, but it turns to a white powder and heat will not turn it black. In fact, if you put aluminum into a salt bath for bluing, the aluminum will disappear, as in dissolve.
The original method for bluing involved using some acid or rust inducing the steel to oxidize evenly, then the steel was boiled in water, then carded (buffed) then the process starts over. Six to ten cycles got you a nice shiny black oxide finish.
The new way of bluing guns involves a solution of Sodium Hydroxide (aka lye) and a nitrate. These nitrates include Sodium Nitrate, Potassium Nitrate or Ammonium Nitrate. This is how virtually all manufacturers blue their guns today.
Sodium Nitrate is used as a fertilizer, in food production, pottery and other industrial applications. Potassium Nitrate is (was) used to make black powder, hot dogs, sausage, corned beef, as a fertilizer and other industrial uses. Ammonium Nitrate is used mostly as a fertilizer, but due to its use in ANFO bombs its access has been restricted.
I use Sodium Nitrate, it is the easiest and cheapest to get. I always buy food or lab grade products as they are the purest.
I have purchased my products from The Essential Depot many times in the past and can recommend them.
The tanks I have are 6" x 6" x 30", built out of mild plate steel by a friend of mine.
When adding the water, it is best to wear your PPE and stand back, the water causes a chemical reaction and puts off a gas.
This would be a good time to talk about PPE. NEVER blue guns without the proper PPE. Not only are the salts hot (nearly 300 degrees), but they are highly caustic, meaning even when cold they can burn you or blind you.
Here is what I recommend.
Arm length chemical resistant gloves
A chemical resistant apron made of rubber or vinyl
A full-face shield
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As soon as you add the water to the salts, they will begin to heat up, you will need to stir them to get the water to mix properly
I soak the parts in boiling water while I wait for the solution to get to 270 degrees, then I put the parts in and let them soak for 30 minutes.
I suspend the parts in the solution using steel wire (rebar tie wire) that has been cleaned and degreased. The wood dowels help keep the parts from sitting on the bottom of the tank.
The small parts go in a basket, I have two of them, the rectangular one is homemade, the round one came from a carburetor washing kit.
Then they go to a worktable or bench to be sprayed and/or soaked in water displacing oil
If you notice some rust on top of the bluing, do not fret, this is not uncommon, simply soak some 0000 steel wool in oil and gently rub the rust off, it should remove easily.
