Hi Splidge
From my experience with working for ICI, proponal, which is basically alcohol anyway, I think (could be wrong as my chemical days are long gone) should not do any harm to an iron blade directly and should remove light oils quite easily. I would imagine that newly bought propanol fresh from the bottle used sparingly would be best. It evaporates quite quickly (use it with good ventalation ie outside) and if you use it do make sure you really give the blade a good wipe to remove all residue as you never know especially with old blades and what they could have been coated with previously. A previous low grade oil with dust and other nasties could have a negative effect if left to its own devices with a solvent. Also propanol in a scabbard could have a negative effect too with woods, glues, dust, laquer etc etc...