Blackening Steel Parts
The Live Steamer, March-April 1950
One of the simplest methods of producing a nice blue-black finish to steel parts is as follows.
Finish the piece by any orthodox method, draw file with a #4 toolmaker file gives the best surface without rounding square corners as emery cloth is liable to do. Then wipe over whole surface with an oily clean rag. Now get a pot of lead melted, allow to stay over the burner a few minutes extra after melting is complete. This will heat the metal a few degrees above the melting point, but don't heat too much. Now plunge the oily piece of bright steel below the surface of the lead. Hold it below for a few minutes until it has acquired the temperature of the lead. Take it out, and the moment it is exposed to the air it will acquire a deep blue black color evenly all over. This kind of finish seems to resist rust to a certain extent. The writer has had two throttle levers in the basement for the past six months, one was a bright finish, the other treated as above. The former is red with rust now, while the other is unblemished.