Rust bluing gives a blue-black protective finish to metals. It is desirable when restoring old guns, antique clocks with metal show pieces and other crafted works made from ferrous metals, such as wrought iron, carbon and some steels. To make a homemade rust bluing solution, you will need access to zinc or manganese dihydrogan phosphate, water, a tank and an oxidizing agent, such as nitrate.
To prepare the phosphate dipping solution, fill a tank with water until 6 inches below the maximum fill level. Add the phosphate, as directed by the supplier. Add more water until you reach the fill level. Heat the solution until it is between 179.6 degrees Fahrenheit and 190.4 degrees Fahrenheit. Add 7.5 grams of sodium nitrate, the oxidizing accelerator, for every 100 liters of water.
Cleaning the Metal
Before you immerse the metal, its surface must be perfectly clean. Even small traces of oil can tinge your metal with yellow. Also, be advised that different types of steel allow will rust in slightly different colors. No amount of hard work and polish will change this. The only way to achieve a unified rust is to rust metals that are the same.
Immersing the Metal
Once the solution is complete, immerse the metal in the heated solution for 45 minutes. For the first 15 minutes, hydrogen gas will be visibly released from the tank. If the visible hydrogen release does not stop after 15 minutes, remove the metal. Once the 45 minutes is up, completely immerse the metal for three minutes in unheated water.
Mixing chemicals can be dangerous. Always know which chemicals you are mixing and what reactions they will cause. If you have any questions, do not proceed until you have consulted the chemical supplier or other expert. Always mix the solution outdoors.