Having a professional gunsmith blue a firearm or other metal can be expensive and rarely yields better results than you can achieve yourself. Gun bluing is used on swords, knives and other metal implements as well, when a midnight blue or black finish is desired.
Cover your table with a plastic tablecloth or dropcloth to protect it from the bluing and other chemicals needed. Disassemble your firearm, clean the entire surface with steel wool, and wipe it clean with acetone.
Gun bluing solutions used to require heating, but cold application is now a viable option. Use cotton balls and swabs to apply gun bluing as evenly as possible over all surfaces. This will prevent drips from running, leaving streaks. Apply several coats to ensure good coverage. According to gunsmith Jon Moran, "I rub the bluing on as if I were polishing brass. Firm pressure and scrub it on. Pressure helps keep the application even and reduces the spotting."
When the blue is even, soak all parts in a baking soda solution for several minutes to neutralize the acids. Rinse with clean water and dry the outside of all pieces with clean rags and the inside with a cloth on your bore cleaning rod.
Lubricate Your Firearm
Soak each piece with a coating of spray lubricant. According to artisan and industrial blacksmith Gypsy Wilburn, who uses gun bluing as a finish on swords and knives, "Get plenty of lubricant into all the holes and slots or rust might develop." Rub down all pieces with gun oil, using clean rags and your bore-cleaning kit. Reassemble your firearm.
According to gunsmith Holt Bodinson, writer for Guns Magazine, "Color sometimes is a function of the time bluing chemicals are in contact with the steel, but most cold blues seem to be self-regulating and simply stop working at a certain point. The point is follow the directions first and then experiment a bit if the results aren't exactly what you want."