Gun bluing is the process that imparts the rich blue-black finish to the metal parts of firearms. There are two methods of gun bluing. Hot bluing uses fairly large vats of boiling acids and is usually the preferred method for professional gunsmiths. Cold bluing can be done with a relatively small investment in equipment and supplies and is the preferred method for hobbyists. Bluing not only gives the gun an attractive finish but protects the metal from rust.
Hot Bluing Techniques
Hot bluing a gun will require three vats or tanks that can be heated to boiling. These tanks need to be large enough to completely submerge the largest part of the gun, usually the barrel, being blued. For this reason the hot bluing process is usually only undertaken by gunsmiths who will be bluing multiple guns.
Prior to submersion in the hot bluing chemicals, the gun parts have to be cleaned, often using hot solvents, to remove all oils and dirt particles. Any contamination on the metal of gun will interfere with the bluing process.
The gun parts are then placed in the hot bluing tank. The longer the gun parts are left in the bluing tank, the darker the finish will be. Use caution when submerging gun barrels. Any trapped air inside the barrel can expand during the hot bluing process and can violently eject hot liquids from the tank.
After gun parts are removed from the tank, they are rinsed in cold and later hot water before a hot oil finish is applied. The gun can then be reassembled.
Cold Bluing Techniques
There are several cold bluing products available for firearm hobbyists. All require the metal parts to be completely clean. Degreasers and solvents are used to accomplish this.
Once the metal is clean, the bluing agent is applied according to the product instructions. Usually the bluing materials are wiped or dabbed on the metal parts using clean, lint-free cloth. Cold bluing materials are often applied in multiple passes. This allows the new applications to overlap previous applications and can be used as a tool to provide a more even and uniform finish. Make as many applications as necessary to reach the color of finish desired.
Once the cold bluing is finished, an oil finish is usually applied.
General Gun Bluing Techniques
Either process requires the metal parts to be clean and rust-free. Even fingerprints on the metal can cause irregularities in the final blue finish to the gun.
Handle all materials used in gun bluing with care. All are solvents or acids and can be dangerous if handled improperly. Follow all instructions and safety precautions included with the product packaging. Work in a well-ventilated area and wear appropriate personal safety gear such as safety glasses and an apron.
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