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David-NY · 03-06-2015, 03:37 PM

I have been trying to get familiar with the different bluing methods used on Luger pistols and want to tap into (and perhaps even contribute to) some of the collective knowledge on this board.

One preliminary issue (based on some of the posts I reviewed) is to clarify precisely what bluing is -- and is not. A bona fide "blue" finish is a metal surface that has been oxidized to form a layer of iron (II) oxide (i.e. Fe3O4 or "black oxide") on its surface. Black oxide does not, in and of itself, impart any protection from corrosion. However, the process of creating a black oxide surface layer results in thousands of microscopic fissures in the surface of the metal. If the metal surface is then impregnated with oil, oil will fill in the fissures and pores and form a film over the surface of the metal. The oil film prevents oxygen from reaching the iron steel, which prevents further oxidation from forming.

The original form of bluing was "rust" bluing which involved creating successive layers of regular old red rust - i.e. ferric oxide, Fe2O3. When ferric oxide is heated over about 200 F it changes to Fe3O4. This is why one step in the rust bluing process is immersion in boling water.

I have a book that says that rust bluing stopped in 1918. There are other books that put the date at 1923. E.g. the discussion here: http://forum.lugerforum.com/showthread.php?t=32819

Later Lugers were blued using bluing salts. This creates a layer of Fe3O4 by oxidizing the surface of the metal in a heated solution that is already sufficiently warm that it forms black oxide rather than red rust.

Frankly there is very little actual (end result) difference between different bluing methods - charcoal bluing, carbonia, etc. All of these processes involve creating a layer of black oxide on the surface. The obvious difference (at least when dealing with Lugers) is going to be that on a rust blued gun the inside of the frame will remain in the white.

In the above link there is discussion of a "built up" bluing method used on some guns starting in 1923. What is this???? The reference to immersion in boiling water suggests that red rust is being converted to black oxide, but references to the finish flaking off don't really make sense. It is true that if the oxidation layer was thin the finish would not last that long (as metal wore off and got beyond the oxidation layer).

Any input?

03-06-2015, 03:37 PM	#1
David-NY User Join Date: Feb 2015 Location: Peoples Republic of New York Posts: 33 Thanks: 4 Thanked 23 Times in 10 Posts	Let's talk bluing I have been trying to get familiar with the different bluing methods used on Luger pistols and want to tap into (and perhaps even contribute to) some of the collective knowledge on this board. One preliminary issue (based on some of the posts I reviewed) is to clarify precisely what bluing is -- and is not. A bona fide "blue" finish is a metal surface that has been oxidized to form a layer of iron (II) oxide (i.e. Fe3O4 or "black oxide") on its surface. Black oxide does not, in and of itself, impart any protection from corrosion. However, the process of creating a black oxide surface layer results in thousands of microscopic fissures in the surface of the metal. If the metal surface is then impregnated with oil, oil will fill in the fissures and pores and form a film over the surface of the metal. The oil film prevents oxygen from reaching the iron steel, which prevents further oxidation from forming. The original form of bluing was "rust" bluing which involved creating successive layers of regular old red rust - i.e. ferric oxide, Fe2O3. When ferric oxide is heated over about 200 F it changes to Fe3O4. This is why one step in the rust bluing process is immersion in boling water. I have a book that says that rust bluing stopped in 1918. There are other books that put the date at 1923. E.g. the discussion here: http://forum.lugerforum.com/showthread.php?t=32819 Later Lugers were blued using bluing salts. This creates a layer of Fe3O4 by oxidizing the surface of the metal in a heated solution that is already sufficiently warm that it forms black oxide rather than red rust. Frankly there is very little actual (end result) difference between different bluing methods - charcoal bluing, carbonia, etc. All of these processes involve creating a layer of black oxide on the surface. The obvious difference (at least when dealing with Lugers) is going to be that on a rust blued gun the inside of the frame will remain in the white. In the above link there is discussion of a "built up" bluing method used on some guns starting in 1923. What is this???? The reference to immersion in boiling water suggests that red rust is being converted to black oxide, but references to the finish flaking off don't really make sense. It is true that if the oxidation layer was thin the finish would not last that long (as metal wore off and got beyond the oxidation layer). Any input?