Why is it necessary, in re-blueing a firearm, to polish the original finish away before applying the new finish? It seems that t

[99explorer]

Why is it necessary, in re-blueing a firearm, to polish the original finish away before applying the new finish? It seems that the new blueing would cover all surface areas where the original finish had worn away.

[Sourdough Dave]

Bluing is a form of oxidation, sort of a controlled rust, so for the oxidation to take place you need to have bare metal.

[99explorer]

You would have bare metal where the original finish had worn away.

[Sourdough Dave]

Sort of like sanding out beyond the bondo on a repaired fender so the finished paint job looks smooth and you can't tell it was ever repaired. After polishing, degrease the surface before applying the bluing compound

[DSMbirddog]

If you don't take it all off you won't get an even blue. If your just touching up you can get a product for that but it won't be a nice even blue black finish. These guys are right.

[99explorer]

This is a theoretical question, and not a practical problem.
Polishing is said to be the most important step in the process. I have no reason to dispute that. I just don't understand why. It seems that after degreasing, the factory polish would suffice before submerging the item in the tank, and only the bare metal would be affected by the salts.

[Hunter Savage]

you dont have to if you are happy with blotches in your final bluing job .

[99explorer]

cooner-
Are you saying that the surfaces that retain the original blueing would be affected by the reblueing action?
Or that the worn surfaces would take the reblueing unevenly?