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What is the Blue Finish on a Firearm?

Updated: Nov 16, 2022

Many revolvers with a blu finish. Most are 50+ years old and in excellent condition. However, some show signs of wear from normal use over the years. Note the wear on the revolver's blued barrel in the center of the top row.

You pay enough for weapons that you want to keep them in good shape. Besides, you want them to fire when you need them to fire. One of the coatings that keeps a gun from rusting and keeps it looking good is bluing. However, even with a blued barrel, you need to keep the firearm clean, including removing fingerprints. The oils from your skin will cause the blueing to start rusting.

What is Bluing, and Why is it Important?

What does blued mean on a gun? Bluing is a coating that manufacturers and gunsmiths put on gun barrels to protect the barrels. The process also improves the aesthetic qualities of a firearm and "repairs" damage on the surface of the barrel. The term comes from the bluish-black finish caused by the chemical reaction from the chemicals used on a steel barrel. Bluing comes in two forms: Hot bluing and cold bluing.

A 100+ year old revolver that has had the bluing worn off over a century of use. The firearm is still in reasonable condition for its age and could use a rebluing to help ensure future protection from rust and pitting.

Hot Bluing

Hot bluing, which is usually done at the manufacturer, involves placing the steel pieces of a firearm into certain chemicals and heating the solution to 302 degrees Fahrenheit (150 degrees Celcius). In most cases, the chemicals used are potassium nitrate and sodium hydroxide mixed with water.

The chemicals cause magnetite – a black oxide – to form on the surface of the metal. The magnetite coating is rust-resistant but not rust-proof. You still need to keep body oils and water off the weapon.

Advantages of Bluing Handguns and Other Firearms

Hot bluing a weapon means that the user does not have to wipe the firearm down every time he or she looks at it or takes it out in the rain. It keeps the firearm from immediately rusting should it get wet. However, you do want to clean it as soon as possible.

Disadvantages of Bluing Handguns and Other Firearms

Hot bluing means working with corrosive chemicals and high temperatures. It needs to be done in a controlled environment. Thus, only manufacturers usually use the hot bluing process, as they have the equipment to do it on a large-scale basis. They also have the personal protective equipment needed to keep the workers safe from chemical and thermal burns.

Another huge disadvantage to hot bluing is that the chemicals are also difficult to dispose of. Finally, hot bluing is not as durable as some other types of finishes – it scratches easier but is also easier to remove and replace with new bluing or another finish.

Cold Bluing

If you have a firearm where the bluing has worn off, you can cold blue your firearm yourself. You do not need heat for this process. All you do is purchase a bluing gel and follow the instructions on the brand you purchase.

Cold-Bluing Advantages

The cold-bluing process is safer for the end-user, and it is an environmentally friendly process. It is not expensive, and you can do it in less than an hour.

Cold-Bluing Disadvantages

With cold bluing, many products are not corrosion-resistant. However, some protection on the weapon is better than no protection. With hot bluing, the process actually creates a layer of oxide. With cold bluing, this does not happen.

It also takes longer to cold blue a gun than hot blue, though it is much less expensive. Finally, cold bluing scratches easier than hot bluing.

How to Blue a Gun with Cold Blue

The process to cold blue a gun is very simple. Remember, you will be working with chemicals, so you should always wear protective eyewear and rubber gloves.

Step 1: Take the gun apart. You can remove the front sight or leave it on. It's pressed in and could be difficult reinstalling it. Plus, you'll have to sight the gun again. Many people leave the front sight on, but remove the rear sight, which is usually held on with a screw. Also, leave the trigger on if it is attached with a pin.

Step 2: Remove the existing bluing with ultra-fine steel wool.

Step 3: Degrease the barrel. The bluing kit should come with a degreaser.

Step 4: Rinse the barrel with cold water and dry it completely.

Step 5: Apply the first coat of the bluing chemical with the included sponge.

Step 6: Rinse the barrel in hot water, then wipe it dry.

Step 7: Gently smooth the bluing with ultra-fine steel wool.

Step 8: Repeat Steps 5 through 7 at least once.

Step 9: Gently buff the newly blued barrel with ultra-fine steel wool until it comes to a shine.

Step 10: Put the gun together and enjoy the newly blued barrel.

How to Remove Rust from a Blued Gun Barrel

Sometimes oil from your fingers or moisture will cause a barrel to rust. If the rust is surface rust on top of the bluing, wipe the barrel down and coat it with gun oil. Wipe the gun oil off.

If the rust doesn't come off because it is deep into the barrel, you will need to remove the old bluing and reblue it. You can choose to have the barrel hot blued or cold blued.

How to Keep a Blued Gun from Rusting

Always clean your firearms after every use. Make sure you use gun oil on the barrels and wipe it off with a soft cloth. Always check the bluing, especially on older guns. You might have to blue the barrel and other metal parts after many years, especially if you use the firearm frequently.

Also, keep your firearms out of moisture. Keeping guns in a case helps keep any moisture in the house from rusting the barrel. If your home has a lot of humidity – moisture in the air – you might have to take extra care of your weapons to keep them from rusting. Cleaning them once every month or month-and-a-half will minimize the chance of the barrel rusting.

How Does Bluing Compare to Other Types of Firearm Finishes?

The market has several types of firearm finishes other than bluing, including:

  • Parkerizing

  • Anodizing

  • Cerakote

  • Duracoat

  • Nickel boron

  • Chroming

  • Specialty plating

  • Quench polish

  • Hydro dipping and skinning

  • Powder coating

Of these, only bluing and chroming score a 10 on attractiveness. None of the coatings received a 10 for durability, though Parkerizing, anodizing, Cerakote, Duracoat, nickel boron, chroming and quench polishing all scored a 9. Bluing came is a 7. Hydro dipping and skinning is the second least durable coating with a score of 5. Powder coating scored a 2 for durability.

Bluing lasts from 2 to 5 years, depending on the moisture content where you store the gun. The finish is water-resistant, as are all of the finishes. Even chrome rusts after a while if you do not take care of it, so we don't consider it waterproof.

With proper care, each of these finishes could last for many years. Blued guns need to be cleaned frequently with gun oil to prevent rusting.

While you can maintain blued finishes and even restore them on your own, sometimes it's a job better left to the experts. X-Ring Supply provides gunsmithing services, so if you need help restoring or touching up a blued finish on your gun, we are happy to help.


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