Salt Blueing~
 

How does this process differ from all the rest and when and on which lugers was it used? Eric

I found this~ http://www.rustblue.com/about/instructions/ A real detailed process! Eric

Explained! https://en.wikipedia.org/wiki/Bluing_%28steel%29

I think that salt based bluing accelerates the controlled oxidation process, probably creating a higher percentage of the blue-black mode of Iron Oxide than the slow rust and card process in the older more manually intensive Rust bluing processes.

The WikiPedia article you found has a pretty good explanation of the different oxidation modes of iron, and why Magnetite (the blue-black mode of Iron Oxide) is a desired finish. Getting there is, of course, half the fun...

As contrasted to the rust bluing process you found described online, salt bluing is done in warmed baths of mixes of chemicals followed by polishing steps.

Brownells has a pretty good summary of the modern process here:

https://www.brownells.com/aspx/learn...aspx?lid=11044


The chemical bath contents and mix levels have varied over the long development of an efficient process, and this also was impacted by the alloy content of the steels being treated (leading to color variations with certain chemical mixes).


Mauser started shifting military contract Lugers to Salt Bluing in 1937, with a mix of characteristics coming over the first part of that year. I'm pretty sure Krieghoff Lugers were salt blued as well but could be mistaken about that.

All my post war modern Mauser Lugers were salt blued.

Even after 1937, Mauser commercial Lugers were rust blued, appearing with strawed small parts. It must have been considered a premium finish at that point. Here's a photo of the rust blued frame from a 1938 dated .30 Luger Mauser pistol from late in the "w" block and a 1938 Military contract Mauser Luger frame and receiver which were salt blued. You can see the metal still in the white inside the commercial Luger frame where the bluing chemicals were never applied. The Military contract Luger shows the bluing throughout the interior of the frame.

Mauser does an excellent job!! Tks for your valuable info!! Merry Christmas!

"As contrasted to the rust bluing process you found described online, salt bluing is done in warmed baths of mixes of chemicals followed by polishing steps. "

No,
items to be hot blued must be polished or "prepared" before bluing. If polished after, all the blue color- which is a very thin "coating" or reacted layer as you described, will be removed and one is back to the "white" state of un-finished metal.

As we all know from experience, hot blue is not a very durable finish; rust blue is a little better as the surface is etched during application.