Cyccommute,
You mention phosphoric acid. There is a solution called Ospho, a dilute phosphoric acid solution, no issue if it splashes briefly on hands, that is a common treatment for rust, it turns the red rust to black iron phosphate, and then you paint over it (I've had issues with cosmetic white "runs" if painting over too soon, the Ospho needs to dry about a week, and even better if first covered with primer). But anyway...
I treated a shiny carbon steel knife with Ospho, to get the vintage look, like carbon steel Sabatier kitchen knives that have been used for decades, graying from many years of slicing acidic fruits, vegetables, and meats. I didn't soak the knife in Ospho, just actively brush it on for several minutes, then rinse and dry, left a nice flat gray finish. So my question is, did this risk embrittlement of the knife? Thanks in advance.
Many years ago I derusted some files with concentrated hydrochloric acid (outside with full PPE), as I recall, made green solution on surface, but then after rinsing and drying, left them on an electric radiator heater a couple hours in case they absorbed hydrogen, wasn't sure if that would cure. Comments?
Last edited by Duragrouch; 02-11-24 at 02:34 AM.