Sodium Thriosulphate (or hypo) is (was?) used as a photographic 'fixer' for black & white photographs.
It also has a useful reaction with steel producing an intense black colour on the surface of the steel. Diluted hypo, warmed to 75 deg C, and ultra cleaned steel swirled about in it produce this reaction in about a minute. Useful for blacking tools and the like.
But what is the reaction ? Is this a deposit (so maybe transient) or is there a reaction with the atoms on the surface of the steel (so hopefully reasonably well bonded)?
I know that it works but what is happening, anyone know?
AWEM