I have a stainless steel kettle that I let boil dry. That is, I left it on a hot coil burner with nothing in it, and noticed a few minutes later that the bottom was red hot and smoking. To make matters worse, I panicked and quenched it with cool water.
Both the inner and outer surface were left discolored with various shades of yellow and purple. This seems to be a known consequence of overheating, but I can't find an explanation of what actually happened.
I understand why heat (especially combined with quenching) would warp the metal, but why would it cause discoloration (that persists after the metal has cooled)?
After hunting around, I saw several suggestions that boiling white vinegar could remove the discoloration, and to my suprise, it worked pretty well. Why does this work?