Cast Iron Pans: The Bluing Process

Bluing is a passivation process that protects steel from rust using a black oxide coating. It is named after the blue-black appearance of the resulting protective finish. The process involves an electrochemical conversion coating resulting from an oxidizing chemical reaction with iron on the surface selectively forming magnetite (Fe3O4), the black oxide of iron. Bluing is used in seasoning carbon steel cookware, to render it relatively rust-proof and non-stick. In this case, cooking oil, rather than gun oil, acts to displace water and prevent rust. The bluing step is essentially the same as gun bluing, which is just a much thicker coat of black oxide achieved by a chemical process.

What is gun bluing?

Gun bluing is a passivation chemical process that protects against rust by putting a layer of black oxide coating on top of the metal. Bluing is also known as black oxidizing. This type of finish ranges in colour from a very dark blue to black, which gives the process its name. It is created by an electrochemical conversion coating that causes an oxidizing chemical reaction with iron. The result is the black oxide of iron called magnetite.

The process of bluing is not a technique only known to gunsmiths. Many people have conducted a bluing process, but never realised they were doing it. For example, if you have ever seasoned a cast iron skillet, you have effectively “blued” it. A cast iron skillet that is properly seasoned has a glazed coating that looks like bluing on a firearm. A properly seasoned cast iron skillet is also rust-resistant and non-stick. The difference is that you are using cooking oil instead of gun oil, but the outcome is relatively the same.

There are several types of bluing processes, including colour case hardening, which creates the mottled finish that you may have appreciated on antique revolvers and rifles. But all bluing processes operate according to the same fundamental chemistry, even if they don’t all yield the same exact colour finish. In addition to case hardening, there are also hot bluing, rust bluing, fume bluing, cold bluing, niter bluing, and browning.

Hot bluing is the most common process for bluing a firearm. This method is the most durable and gives the best protection to the firearm. First, the firearm is disassembled and cleaned. The gun parts are then soaked in a warm bluing solution for about 30 minutes. The bluing solution is a caustic salt mixture of potassium nitrate and sodium hydroxide and is warmed to 275-310 degrees Fahrenheit. The parts are then rinsed and dried and placed in boiling water for about 45 minutes. The last step is to soak the parts in an oil bath for about an hour. The newly blued gun is now ready for reassembly.

Cold bluing is a process that does not require heat. It provides the least protection of all the bluing techniques. This type of bluing also does not hold up well if the firearm is carried in a holster. Cold bluing is more effective when doing small areas on the firearm. It is good for touching up areas if the gun is oiled on a regular basis. To cold blue, the part of the firearm to be blued needs to be thoroughly cleaned, then sanded smooth. The bluing compound is then applied to the area. The bluing is then lightly sanded to blend in. Gun oil can then be applied to the area.

How does it work on cast iron pans?

Cast iron pans can be seasoned to create a black non-stick coating. This is achieved by causing thin layers of flaxseed oil to polymerize and bond to the iron. The oil bonds better to the pan when the pan is covered with magnetite rather than blank iron. This is due to the porous nature of the oxide layer.

One way to create magnetite on a cast iron pan is through a process called "rust bluing", which is used in gun manufacturing. This involves encouraging the formation of a thin layer of Fe2O3 (red oxide) on the gun barrel, which is then immersed in boiling distilled water. The lack of dissolved oxygen in the water causes the Fe2O3 layer to convert into Fe3O4 (black oxide) within minutes.

However, when attempting to apply this process to a cast iron pan, the Fe2O3 layer stays red and does not turn black. This may be due to a difference in materials, i.e. cast iron vs. gun steel. To successfully apply rust bluing to a cast iron pan, additional steps may be required, such as "carding", where the steel is rubbed or brushed to remove larger rust structures, and repetition of the process multiple times.

Another method to create magnetite on a cast iron pan is to heat the polished and cleaned pan on a stove, which will oxidize the surface and form magnetite. The oxide layer can be grown in thickness by adjusting the temperature.

Once the magnetite layer is formed on the cast iron pan, the pan should be completely clean and dry before the first layer of seasoning is applied. This involves heating the pan sufficiently to dry it and open the pores. After this step, a coat of oil (such as flaxseed, lard, or ghee) is applied and wiped off. The pan is then put back in the oven at a temperature between 350-450 degrees Fahrenheit. This process of heating and wiping is repeated multiple times to ensure an even coating and to prevent blotching.

After cooking on the pan, it is recommended to wipe it dry and put it back in the oven at 450 degrees Fahrenheit for an hour. This helps to create the next coat, which comes from the polymerization of the oil during the cooking process.

By following these steps, a cast iron pan can be successfully seasoned, resulting in a non-stick and durable coating.

What are the benefits of gun bluing?

Gun bluing is a process that improves the condition and aesthetic qualities of damaged metal surfaces on a wide range of hobbyist equipment. It is a passivation chemical process that protects against rust by putting a layer of black oxide coating on top of the metal. The process is typically segmented into two distinct categories: 'cold bluing' and 'hot bluing'. Here are the benefits of gun bluing:

Protection from Corrosion and Wear

Bluing provides a layer of protection for the raw steel used in many gun parts. It is a passivation process that converts steel to create a thin protective shell around it, preventing rust and other factors that could cause damage. This protective finish shields steel parts from corrosion, helping to maintain the metal finish by resisting superficial scratching.

Improved Aesthetics

The blue/black finish that results from the chemical reaction after applying the gel to a steel surface enhances the appearance of steel items. This can be especially beneficial for small businesses looking to entice customers to buy their metal products.

Cost-Effectiveness

Cold bluing is a convenient, cost-effective, and environmentally friendly alternative to hot bluing. It does not require heating and can be easily applied to achieve a quick, effective blue finish.

Ease of Application

Cold bluing can be purchased as a gel and easily applied to any steel equipment, making it perfect for owners of small to medium-sized gun collections. It is also safer than hot bluing, which requires handling extremely hot chemicals that can be challenging to dispose of without harming the environment.

Durability

Hot bluing, the industry standard for bluing, is a very durable finish applied to a variety of steels. When combined with oil, it is an excellent rust preventative, extending the life of a gun.

In summary, gun bluing offers a range of benefits, including protection from corrosion and wear, improved aesthetics, cost-effectiveness, ease of application, and durability. It is an important process for gun enthusiasts and manufacturers, enhancing both the functionality and appearance of firearms.

What are the alternatives to gun bluing?

There are several alternatives to gun bluing, each with its own advantages and disadvantages. Here are some of the most popular options:

Parkerizing

Parkerizing, also known as phosphating or bonderizing, is a process that provides a tougher finish than bluing and offers increased resistance to corrosion, nicks, and scratches. It involves dunking steel gun parts into a heated bath of phosphoric acid solution, which results in a matte finish ranging from medium gray to dark black. While it offers better protection than bluing, it still benefits from a coating of oil for smooth operation.

Metal Plating

Metal plating is a process that has been used for centuries to deposit a thin layer of one type of metal onto another. Nickel plating, for example, offers corrosion resistance and can be polished to a bright shine. Hard chrome is another popular option, known for its toughness and ability to extend the working life of high-velocity rifle bores. For decorative purposes, silver and gold plating are also options, though these soft metals are best reserved for display pieces. Titanium nitride finishes offer a similar level of toughness to hard chrome with the added benefit of a polished, lustrous finish.

Stainless Steel

Technically not a finish, stainless steel is a type of steel with corrosion resistance built into it due to its high chromium content. While it tends to be more expensive than blued finishes, it is a good option for guns used regularly in harsh weather conditions.

Cerakote

Cerakote is a popular coating option that is composed of a polymer-ceramic compound. It can be airbrushed onto gun parts and then cured in an industrial kiln, resulting in a smooth, matte or gloss finish in a variety of colors. Cerakote provides a hard, durable finish that is resistant to wear, corrosion, chemicals, and impact damage. It also improves lubricity, reducing friction between moving parts. One of its biggest advantages is its versatility, as it can be applied to various materials such as wood, polymer, and aluminum, making it ideal for treating an entire rifle.

Paint

A simple and cost-effective alternative to bluing is to use spray-on, bake-on paint. Rust-oleum oil-based paint is a commonly used option, but there are also more durable bake-on finishes available in various colors from companies like Brownell's Gunsmith Supply. These finishes are easy to apply, prevent rust, and can be easily reworked or touched up. However, they may not be as durable as some of the other alternatives mentioned above.

What is the history of gun bluing?

The history of gun bluing dates back to the early days of gun-making, when people sought ways to protect the iron and steel parts of their weapons from rust and corrosion. There are two main types of bluing processes: cold bluing and hot bluing. Cold bluing involves coating the gun parts with an acid solution, allowing them to rust uniformly, and then immersing them in boiling water to stabilise the process. This method was often used by gunsmiths in the 19th century before the development of hot bluing. Hot bluing, on the other hand, is a more modern and economical process adopted by larger firearm companies. It involves immersing steel parts in a hot solution of potassium nitrate, sodium hydroxide, and water, and stainless steel parts in a mixture of nitrates and chromates. This method provides better rust resistance and a more permanent finish.

The term "bluing" is derived from the blue-black appearance of the protective finish created by the process. While the technique was refined over time, its origins can be traced back to ancient Japanese swords and European straight razors. The process allowed Samurai to keep their weapons free from rust, even during prolonged battles. In Europe, the technique of browning or russetting, which involved applying a solution to the outside of the barrel and allowing it to rust, was adapted to create a dark blue/black finish, thus the term "bluing".

Over time, various formulas and techniques for gun bluing were developed, with each manufacturer using different steel alloys and processes to achieve the desired results. Today, bluing is still used by gun manufacturers, gunsmiths, and gun owners to improve the cosmetic appearance and provide corrosion resistance. However, modern coating technologies like Cerakote are gradually replacing blued steel as the primary method of preservation in modern firearms.

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