Making steel turn black without actually applying paint to the surface is a trick that you must execute carefully. This is because you aren't actually applying a surface treatment to the steel, but by quenching it in a bath of used motor oil. Obviously, this presents some hazards. You should never attempt to blacken steel in this way indoors. In addition, it is best to keep a fire extinguisher nearby. This process should not be used on hardened steel, as it removes the steel's tempering.
Grip the steel part with the jaws of the channel locking pliers, being careful to avoid marring the steel. Soft decorative steels in particular can be easily damaged by the hardened tool steel of your pliers. You cannot, however, place anything between the jaws of the pliers to protect it.
Fill a bucket with used motor oil that will accommodate the size of the part that you are blackening. This is necessary because you have to completely submerge the part into the motor oil for it to apply the right colouration.
Heat the steel part with the propane torch until the entire part glows dark red.
Thrust the steel part quickly into the bucket of used motor oil and at the same time release the channel lock pliers. Step back from the bucket quickly. The heat of the steel part will temporarily inflame the oil in the bucket. Put down the pliers and cap the bucket with its lid. This will remove most of the oxygen from the bucket, extinguishing the flame. Allow the oil and the part to cool together for five minutes before removing the bucket lid.
Wipe the steel part off with a clean rag, being careful to clean away all of the oil before using the part for its intended purpose. It should now be blackened to a deep charcoal colour.
Perform this work somewhere outside where there is no overhanging foliage and away from buildings or flammable materials. One of the best places might just be the middle of your driveway.
The hot oil will catch fire when you quench the part within. Move quickly and wear safety gloves and goggles to prevent burns. In addition, have a chemical fire extinguisher close at hand in case of emergencies.