Steel is used extensively in a variety of products from gun metal to hobby crafts. Unfortunately, steel is vulnerable to rusting, which discolors the product and deteriorates the material. Blackening, or adding a black oxide finish to the steel, helps prevent steel from rusting by creating a chemical reaction on the metal surface. This coating inhibits rusting and allows for additional paint finishing that will not be undermined by the rusting process. Black oxide can be finished by a cold process that can be done at room temperature.
Remove any rust with a wire brush or sandpaper. The cold black oxide process requires that you start with clean parts.
Clean the steel pieces carefully to remove dust, solvent and oil residues. Mix a mild detergent and water solution and gently wash all metal surfaces with a soft cloth. Wipe dry.
Prepare the black oxide solution as directed on the package.
Immerse the steel parts into the tank of black oxide finish chemicals.
Allow the chemicals to penetrate the steel surface. Read package directions to determine length of immersion for specific materials.
Fill the rinsing tank with plain water. The tank should be large enough to fully immerse the parts that will be rinsed.
Remove parts from the chemical solution with tongs and place them into the rinsing tank. Allow the parts to set for 10 minutes, moving the parts around with tongs to ensure that all metal surfaces get a thorough rinsing.
Remove parts and allow them to dry thoroughly.
Coat with penetrating sealer using a brush or by dipping into the sealer. Shake off excess sealer. Allow to dry thoroughly.
Apply primer and paint as desired
Cold black oxide kits can be used on forged steel, cast iron, mild steel, hardened tool steels and powdered metal parts, according to CaldwellPlating.com.
Racks can be placed in the solution tanks to allow for complete coverage of the parts.
Penetrant sealers used after the cold black oxide process can leave an oily finish, according to Modern Machine Shop Online. Other types of sealants are available that provide a non-oily finish that may be more suitable for the application of additional coatings.
Cold black oxide treated parts can be welded without danger of toxic fumes.
Wear rubber gloves, goggles and clothing protection to prevent injury from caustic chemicals.
Both the chemicals used in the black oxide process and those used in rinsing the pieces must be disposed of according to local community regulations. Consult with local environmental control agencies to meet their requirements.
The cold black oxide process does not provide as durable a finish as titanium nitride or other tough coatings. According to SWDInc.com, black oxide coatings are not suitable for severe outdoor conditions or corrosive environments.