Just read a bit about passivation. Passivation is the dipping of stainless steel products immediately after manufacture in citric acid to remove any traces of free iron on the surface of the stainless steel. This results in a thin outer layer of pure chromium, which does not rust/tarnish. If I understand correctly, this outer layer cleansed of free iron is called a chromic oxide layer. Stainless steel treated by the chemical process of passivation is nearly impervious to rust, unless the chromic oxide layer is breached, or unless the citric acid bath did not remove all the free iron.
It occurred to me that some old stainless steel knife blades have rust pits, or stains.
Question: Has anyone tried to repeat the passivation process on old stainless steel pocket knife blades, as part of rehabilitating them?
I wondered if re-passivation might remove the rust, stains, etc., and restore a blade?