Let's talk bluing

[Paladinpainter]

4 Scale,
I suppose "blue" is in the eye of the beholder, but to mine there is a substantial difference in color between a caustic and rust blued gun. Caustic 'blue' produces a flat black finish with very few blue highlights, while the old rust blue - like you find on a 1920s era DWM - is distinctly blue to blue/grey.
The chemicals used in today's rust bluing solutions and the old time ones are different. To my tired eyes, the modern rust blue solutions result in a black finish. Thats why, Markbritt's discovery that the addition of sodium nitrate to Brownell's Rust Blue would create blue highlights was noteworthy. (See his sticky in this section)
The old bluing formulas contained stuff like copper sulfate, ethyl nitrate, and mercuric chloride, chemicals you dont commonly find in the modern solutions. My view is that the inclusion of these chemicals creates a molecular structure on the surface of the steel that reflects the blue part of the spectrum.
I think if you were to put a 1920 Luger and a 1940 Luger side by side in natural light, you'd see a difference.
Regards,