Fire bluing, or 'Nitre blue'?
 

It appears from my 'research' that Borchardts, and perhaps early Lugers were 'blued' by way of the above process using potassium nitrate, or 'saltpeter'. If I understand the process, it seems that it is merely a controlled immersion heating process rather than a chemical reaction. For example, I've 'case hardened' BP gun frames just using a propane torch. Supposedly, Spectricide stump rotting chemical is a source of potassium nitrate. I saw a Youtube example of a guy coloring small parts in a pot, the potassium nitrate was hard like solid rosin before heating. I guess the blue occurs around the 700 degree F range and is only a way creating a large, constant heat for an entire gun, as opposed to small parts. I tried some of the Laurel Mountain Browning on a sample and it is too black for my Borchardt project. I've never seen, first hand, any 'early' Lugers, or other examples of the nitre blue process. I think I read early Winchesters were done by this process too. Anyone tried this? Bill

'Fire Blue'
 

This is what I call fire blue, just a propane torch

I have used a small propane plumbers torch for many gun parts...Strawing and fire bluing. I very nice result can be achieved if you pay attention. I clean the parts very well with alchohol and lay them on a clean soft firebrick. Run the torch over the part and you can watch it turn colors. Be careful not to over focus the flame directly on the small part. Slow and steady. Take the flame off earlier than you think..the part will continue heating with the flame off and sometimes get darker than you want.
I don't know about larger parts like frames and cylinders..I never tried any of those. You might want to try a toaster oven
for larger parts for a more controlled heat.

It works. I should have mentioned the entire Walker above is 'fire blued'. Also should have mentioned, I also use a Mapp gas torch. By hold the flame on one small place, I can create the color case hardened effect, moving it when color starts to change. After 10 years or so, the color on the barrel is starting to wear off.

I don't think Borchardts or Lugers were ever done by the nitre method...I have a Uberti 1873 done that way, and the blue is verrry bright and brilliant, but very fragile and wears off easily. I've been experimenting with 5 different rust bluing solutions including Laurel Mountain, and I'm going nuts trying to get a blue finish and not a black one. Thor says he has found the "secret" process of doing it, but of course he's holding it as a trade secret. I'm stumped.

Thor has found a nearly perfect match for the early DWM rust blue. Borchardts are not fire blued, they are rust blued. Springs, pins and sights were fire blued but not the gun.

To illustrate what Ron said, here's the difference between fire blue and rust blue. Regards, Norm

Can never find what I want! There was a Borchardt on the web with close-up pics labled: 'Fire Blue'. That and something I read referrred to the process led me to think that was what was done.

rust blue?
 

About 15 years ago, or so, I rust blued my carbine with some 'german rust blue' I bought from a guy running a small ad in Shotgun News. Was easy and made a satiny finish. It was in a small bottle and a thick, kind of beige color. Not sure if pics do it justice, dark, but not black.

The small parts were fire blued, not the whole gun. "Fire Bluing" can also be done in your kitchen oven if it will heat up to 550 degrees. I do strawing and fire bluing in my electric kitchen oven. If you don't get the color just right, it polishes off easily and can be redone. The secret to a good job is a high polish and absolutly clean of any oil (including body oil from your fingers!)

Examples of "Fire or Nitre Bluing"
 

The Single Action has all parts except for the casehardened frame & hammer Nitre Blued.

Discussion of various surface treatments at this website http://www.runniron.com/index_cowboy.html I was looking for local chrome platers for a customer's M/C parts and found it, perhaps at the exact moment this thread got started yesterday! Look in the Restoration section.