This early surface treatment involves placing steel or iron components inside a sealed retort and exposing them to superheated steam. The steam oxidizes the metal surface, and a subsequent flush of carbon monoxide reduces any higher oxides back to a stable, uniform layer of magnetite. The resulting blue-black finish resists atmospheric corrosion and serves as an excellent base for oil or wax sealants.
We found some old architectural ironwork that still has its original Bower-Barff process finish intact after all these years.
While largely replaced by other conversion coatings, you will still see this finish on historic cast iron hardware and structural fittings.
Related terms
Bonderize
To treat a steel surface with a phosphate conversion coating to improve paint adhesion and corrosion resistance.
Mill scale
Blue-black iron oxide skin formed on steel during hot rolling, which must come off before painting.
Hot-dip galvanizing
Coating steel by dipping it in molten zinc, forming bonded zinc-iron layers that protect by barrier and sacrifice.