Bluing creates a thin layer of black iron oxide (magnetite) on the surface of steel parts. This controlled oxidation passivates the metal to protect against rust and provides a dark cosmetic finish. It is typically done in hot alkaline salt baths and requires regular oiling to maintain its protective qualities.
Heard on the job
We need to blue these receiver blanks before they go to assembly.
Insider tip
True bluing does not add measurable thickness to the part, making it ideal for precision firearms and tooling.
Also heard as
- Bluing
- Black oxide