Rust bluing, temperature and humidity

Olle · 04-26-2010, 09:30 AM

New member here, working on old guns as a hobby and a side business. No Luger yet, but planning to get one as soon as "the right one" shows up...

I have had good luck restoring old firearms using the slow rust method, but I'm still experimenting with it to get a more controlled process. My shop is in the basement where the humidity and temperature can vary quite a bit, so this weekend I built a temperature controlled cabinet. I haven't tried to rust anything yet, but a few test runs show that I can maintain a given temperature quite well. The humidity control is still on the drawing board, so until I can get a humidifier installed I'll just use a hot pan of water, spray bottle or whatever it takes to get the right humidity.

My first question is what the ideal temperature and humidity would be. I usually use Pilkington or Brownells, and they both seem to work quite well under average shop conditions (65-70F, 45-50% RH). It's still a bit of a hit-or-miss proposition, and I assume that raising the temperature and humidity to a constant level would give me more consistent and predictable results. The few brief test runs show that I can get at least 90F in the cabinet, but I will need to experiment a bit to find out what the max humidity can be.

The second question is how to achieve the right color. I usually get a graphite black, sometimes with a slightly blue tint to it. It seems like the color depends on the type of steel rather than the method used, but I figure that there would be a way to get this blue color on any kind of steel given the right rusting solution and temperature/humidity conditions. I have searched the forum, and I get the impression that this is a well guarded secret, but I'm still hoping that someone can lead me in the right direction.

Any advice will be appreciated!

Paladinpainter · 05-02-2010, 09:07 AM

Hey Ollie~
I've been struggling with the same issues all winter and I've stumbled onto some encouraging results.

I use a clear vinyl "greenhouse". I think it is used to starting seedlings indoors. I use a steam humidifier, turning it on/off as required. When the vinyl steams up, I turn it off; let it sit until they clear and then back on again. It takes me about 3 hours to get a good coating of red fuzz at 65 +/- degrees.

I was about to start mixing my own bluing agents because, like you, I you I wanted a bluer tone. By chance, I looked at the components of some Aquafortis I had: water, nitric acid, and hydrochloric acid....classic bluing solution. This stuff is very aggressive and I'm diluting it with water. ( It will still ruin your manicure.)

In my eyes, the results have more deep blue tones. Keep experimenting and let me know what happens.

alvin · 05-02-2010, 09:28 AM

I tried Brownell agent (the cheaper one, $10 per bottle). No matter what I do, the end result color tone is incorrect, showing more brown color, and if repeat a few more times, it turn into very black, and never showing correct grey-blue color tone.

(Not tried on guns, but on 4140 carbon steel)

Olle · 05-11-2010, 08:38 AM

That aquafortis solution sure sounds interesting, it appears to be similar to one of the formulas in Angier's book (starts with a "Z", can't remember the name of it right now...). I have also seen some comments saying that Mark Lee’s gives a slightly blue color, but haven't tried it yet. I spoke with a gentleman at a gun show a while back, and he was somewhat reluctant to give me the whole story, but one thing he told me was that he rusted at a temperature around 95-100F so this is one of the baselines for my experiments.

I have had a problem with the reddish color as well, and I sure ain't a chemist but this seems to be caused by the quality of the water. From what I have gathered, there are basically three kinds of oxides: A somewhat unstable red ("regular rust"), a more stable black (the kind we want), plus a stable, red oxide that can occur if you boil in water that contains certain minerals. I have boiled in tap water with mixed results so I assume that the water quality can vary. To be safe, I have started using distilled water, it's cheap insurance at 85 cents/gallon.

I have experimented some more with my rusting cabinet, and I did get some very encouraging results. By cranking it up to about 90-95 degrees, I can get what I consider a good rust (black with a distinct hue of red, that's where I usually want to boil) in about 30-45 minutes. I kept the humidity at 40-45%, as anything more than that seems to cause condensation on the parts.

I use two heat sources: One cheap cooktop from Wallyworld to get it up to temperature quickly, and one thermostat controlled IR-lamp from Petco (look in the isle where they keep the reptile stuff) to maintain a constant temperature. I would like to get a steamer, but for now I simply spray some distilled water on the cooktop to adjust the humidity. The cabinet is a simple plywood box, with plexiglass panels in the door so I can easily watch the progress. I might post some pictures of the setup later, once I have figured out how to use it.

markbritt · 05-11-2010, 11:55 AM

Guys:

I too had the same problems using Brownells rust blue. The color was inconsistant. Finally, after messing around for quite some time, I converted over to higher temperature Nitre bluing. The results are spectacular as I have been running some test barrels through the process. Once I get a few more under my belt, I may hang out a shingle to do C96, Lugers and P-38's.

Mark

Olle · 05-11-2010, 01:36 PM

In my experience, there will almost always be differences in the color or the appearance of the rust bluing. Some of this can obviously be controlled, but the steel quality seems to be just as important as the method or the bluing solution used. For example: I blued two guns, one right after the other, and used the same method and the same bluing. One came out black, the other one had that nice, blue tint. I have also seen variations in color between different parts on the same gun, blued at the same time but still coming out slightly different.

04-26-2010, 09:30 AM	#1
Olle User Join Date: Feb 2010 Location: Tennessee Posts: 1,149 Thanks: 159 Thanked 664 Times in 318 Posts	Rust bluing, temperature and humidity New member here, working on old guns as a hobby and a side business. No Luger yet, but planning to get one as soon as "the right one" shows up... I have had good luck restoring old firearms using the slow rust method, but I'm still experimenting with it to get a more controlled process. My shop is in the basement where the humidity and temperature can vary quite a bit, so this weekend I built a temperature controlled cabinet. I haven't tried to rust anything yet, but a few test runs show that I can maintain a given temperature quite well. The humidity control is still on the drawing board, so until I can get a humidifier installed I'll just use a hot pan of water, spray bottle or whatever it takes to get the right humidity. My first question is what the ideal temperature and humidity would be. I usually use Pilkington or Brownells, and they both seem to work quite well under average shop conditions (65-70F, 45-50% RH). It's still a bit of a hit-or-miss proposition, and I assume that raising the temperature and humidity to a constant level would give me more consistent and predictable results. The few brief test runs show that I can get at least 90F in the cabinet, but I will need to experiment a bit to find out what the max humidity can be. The second question is how to achieve the right color. I usually get a graphite black, sometimes with a slightly blue tint to it. It seems like the color depends on the type of steel rather than the method used, but I figure that there would be a way to get this blue color on any kind of steel given the right rusting solution and temperature/humidity conditions. I have searched the forum, and I get the impression that this is a well guarded secret, but I'm still hoping that someone can lead me in the right direction. Any advice will be appreciated!

05-02-2010, 09:07 AM	#2
Paladinpainter User Join Date: Nov 2009 Location: Vermont Posts: 64 Thanks: 14 Thanked 45 Times in 15 Posts	Some good luck Hey Ollie~ I've been struggling with the same issues all winter and I've stumbled onto some encouraging results. I use a clear vinyl "greenhouse". I think it is used to starting seedlings indoors. I use a steam humidifier, turning it on/off as required. When the vinyl steams up, I turn it off; let it sit until they clear and then back on again. It takes me about 3 hours to get a good coating of red fuzz at 65 +/- degrees. I was about to start mixing my own bluing agents because, like you, I you I wanted a bluer tone. By chance, I looked at the components of some Aquafortis I had: water, nitric acid, and hydrochloric acid....classic bluing solution. This stuff is very aggressive and I'm diluting it with water. ( It will still ruin your manicure.) In my eyes, the results have more deep blue tones. Keep experimenting and let me know what happens.

05-02-2010, 09:28 AM	#3
alvin User Join Date: Jul 2007 Location: US Posts: 3,843 Thanks: 132 Thanked 729 Times in 438 Posts	I tried Brownell agent (the cheaper one, $10 per bottle). No matter what I do, the end result color tone is incorrect, showing more brown color, and if repeat a few more times, it turn into very black, and never showing correct grey-blue color tone. (Not tried on guns, but on 4140 carbon steel)

05-11-2010, 08:38 AM	#4
Olle User Join Date: Feb 2010 Location: Tennessee Posts: 1,149 Thanks: 159 Thanked 664 Times in 318 Posts	That aquafortis solution sure sounds interesting, it appears to be similar to one of the formulas in Angier's book (starts with a "Z", can't remember the name of it right now...). I have also seen some comments saying that Mark Lee’s gives a slightly blue color, but haven't tried it yet. I spoke with a gentleman at a gun show a while back, and he was somewhat reluctant to give me the whole story, but one thing he told me was that he rusted at a temperature around 95-100F so this is one of the baselines for my experiments. I have had a problem with the reddish color as well, and I sure ain't a chemist but this seems to be caused by the quality of the water. From what I have gathered, there are basically three kinds of oxides: A somewhat unstable red ("regular rust"), a more stable black (the kind we want), plus a stable, red oxide that can occur if you boil in water that contains certain minerals. I have boiled in tap water with mixed results so I assume that the water quality can vary. To be safe, I have started using distilled water, it's cheap insurance at 85 cents/gallon. I have experimented some more with my rusting cabinet, and I did get some very encouraging results. By cranking it up to about 90-95 degrees, I can get what I consider a good rust (black with a distinct hue of red, that's where I usually want to boil) in about 30-45 minutes. I kept the humidity at 40-45%, as anything more than that seems to cause condensation on the parts. I use two heat sources: One cheap cooktop from Wallyworld to get it up to temperature quickly, and one thermostat controlled IR-lamp from Petco (look in the isle where they keep the reptile stuff) to maintain a constant temperature. I would like to get a steamer, but for now I simply spray some distilled water on the cooktop to adjust the humidity. The cabinet is a simple plywood box, with plexiglass panels in the door so I can easily watch the progress. I might post some pictures of the setup later, once I have figured out how to use it.

05-11-2010, 11:55 AM	#5
markbritt User Join Date: Oct 2009 Location: NW Indiana Posts: 240 Thanks: 5 Thanked 48 Times in 22 Posts	Guys: I too had the same problems using Brownells rust blue. The color was inconsistant. Finally, after messing around for quite some time, I converted over to higher temperature Nitre bluing. The results are spectacular as I have been running some test barrels through the process. Once I get a few more under my belt, I may hang out a shingle to do C96, Lugers and P-38's. Mark

05-11-2010, 01:36 PM	#6
Olle User Join Date: Feb 2010 Location: Tennessee Posts: 1,149 Thanks: 159 Thanked 664 Times in 318 Posts	In my experience, there will almost always be differences in the color or the appearance of the rust bluing. Some of this can obviously be controlled, but the steel quality seems to be just as important as the method or the bluing solution used. For example: I blued two guns, one right after the other, and used the same method and the same bluing. One came out black, the other one had that nice, blue tint. I have also seen variations in color between different parts on the same gun, blued at the same time but still coming out slightly different.