Mark,
I think that this could be stated better by "Thor", but I'll try.
Rust blue is a very tricky process that is very time and labor demanding, and also easily messed up. in addition it is not as tough as the salt blue process.
Tha Salt Blue process is to describe it in simple terms simply dipping the parts into a hot *Salt* solution for a few minutes, neutralizing it, steel woolbuffing and oiling.
Rust Blue Is accomplished by Lightly coating the parts with an *acid* solution and hanging in a temrrature and moisture controlled chamber until a rust coat is generated.
this is steel wool buffed and and recoated and returned to the chamber to repeat the process.
this is continued many times until the coating is satisfactory and the part is neutralized, dried, steel wool buffed and oiled.
*Salt* and *Acid* are Basically nitric acid and hydrochloric acids and the salts are nitrate salts.
Two exactly opposite approaches to obtaining an Nitrous Iron oxide coating as the surface of the steel. Nitre is the constituent that renders the oxide blue in color.
I apollogise for the poor explanation of a very complex subject.
But I think I have sucessfully described the relative complexity of the two processes and this explains why most modern guns are treated by processes that resemble the "Hot Dip Method"
ViggoG
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