Originally Posted by
Patrick Chadwick
I think a bit of clarification might be useful for beginners in rust removal. What follows is a gross simplification, from the point of view of a serious chemist or metallurgist, but it will serve for our efforts to restore rusted chunks of metalwork.
The surface known as "bluing" is a very thin layer of ferrous oxide, FeO, a black substance. The "blue" arises from light passing through the semi-translucent layer, which is very, very thin, and therefore fragile. Thicker layers are dead black.
Ferric oxide, Fe2O3, usually found in the hydrated form, Fe2O3.H2O, is the our common-or-garden RUST. This can also be written in rearranged form as Fe(O)OH, which indicates how it can be broken up.
Electrolytic rust removal is therefore doing this
Fe2O3.H2O ----- 2FE + O2 + H2
In other words, free oxygen and hydrogen are produced at the electrodes.
Obviously, if substantial quantities of the hydrogen and oxygen were to recombine – thanks to fire or an electrical spark for instance, the result could be explosive. Hence the general safety advice to keep your electrolytic cleaning bath at a low level – generating bubbles, but not boiling away! And in a well-ventilated area, of course.
The finish-friendliest way to remove rust off old gun parts is to use electrolytic cleaning. Accompanied by ultrasonic cleaning to remove loose particles, it will clean up corners that are in accessible by mechanical means. Search the forum for my contributions on "electrolytic cleaning" and "Anschutz" and you will find a good example of the use of this method.
I.M.H.O. mechanical methods (wire wool, wire brushes etc) should be regarded as a last resort.
