Charcoal Bluing (updated 7-18-18)

[David Rase]

I started gathering parts about 6 months ago to build an oven to charcoal blue barrels in.  On the 4th of July I finally got a chance to start the process of trial and error.  I currently have done 4 cycles working through different variables.  Current information out there has people using temperatures anywhere from  700 degrees f to 900 degrees f.  Soak times also varied from 1 hour to 3 hours. 
Below is a photo of my oven with PID controller and a hand held pyrometer.  Since my PID controller is not a ramp soak I use the hand held pyrometer to monitor temperature during the cool down cycle.


For my first attempt I started out conservatively using a temperature of 700 degrees f and soaking for 1 hour once I was up to temperature.  I used a 7/8" hex bar of 12L14.  Results were not even close to what I was anticipating.  The blues were splotchy and there was no color what so ever at the ends of the barrel.  Though my oven was heavily insulated, the end caps were not so I made some insulation caps for the ends to help maintain the heat at the ends of the oven.


On my second attempt I raised the temperature to 750 degrees f.  I got better coverage this time with the higher heat but the results were still disappointing.  The blues I got were more of a temper blue than a charcoal blue.  I came to the conclusion that a 1 hour soak once the oven reached temperature was not enough time for the wood charcoal to activate and emit any gasses.  Armed with that information I moved onto attempt number 3.
Photo of cycle #1 top and cycle #2 bottom.


This third go round I left the temperature at 750 degrees f but increased the soak time to  3 hours.  Upon removal of my test barrel from the oven I had results that were usable.  Though usable there was still too much bluish grey and not enough blue  for my liking.
Again shown with cycle #1 for comparison.


Onward to cycle number 4.  Increase the temperature to 800 degrees f and soak for 3 hours.  Finally, utopia.  A nice blue the full length of the barrel.  Though there are still some lighter areas, not spots, this blue is a keeper.  Due to this cycle not cooling down until around until just after midnight on Saturday I opted to wait until Sunday morning to remove the barrel.  Had I removed the barrel while it was still warm, around 200 degrees f on the thermocouple reading, I think I would of been able to blend in the couple of dark and light areas with lime, oil, steel wool or scotch bright pad.  We will see if this theory works when I make run number 5 on Tuesday.
Overall view of cycle #4.

[rich pierce]

Cool setup and great info!

[ChipK]

Looks great Dave, it will be interesting to see what difference the lime makes when the barrel is still warm.

[Marcruger]

I can totally understand that some of those results were not what you are after, but man they'd look good rubbed back slightly on the edges with a ScotchBrite pad to simulate wear.  Isn't it funny how a failed project can produce something cool in its own right.  God Bless,   Marc

[JPK]

Very nice set up. What little char coal bluing I’ve done has been pistols. My best results were a 3 hour soak at 800* then let it cool over night in the oven. I removed the parts that were all hung on wires and let them age for two days then oiled with machine oil. Rather dark blue and even.

[Eric Kettenburg]

That's extremely interesting.  Now I have not approached this with any type of specific precision as you have done, but I have done this with an awful lot of barrels in a charcoal fire and I'm pretty sure I am going higher than 800 degrees.  Your final barrel looks really good, so I wonder if that is the *minimum* required to get a proper blue.  Were you able to observe the barrel while it was being heated and determine whether or not there was any "glow" to it?  I believe I have been doing this at what old-timers usually called a 'black-red' heat, in other words if you were to view the barrel in a dark room, you would begin to think you were seeing a faint transition into a very faint red glow.  I'm pretty sure that doesn't happen until @ 1000 degrees.  Your setup looks really interesting and I'd like to know more about it - how it's constructed etc.  Propane for fuel?

[jerrywh]

 Dave.
   If you remember I did tests on barrel specimens for about  a month and a half In a oven and in a charcoal bath of different sizes.  I have it all on a thumb drive. However I did not try the type of setup you have.  Dave Crisalli recommended the type setup you have. More later.

[David Rase]

Eric,
I agree,  think I should still go a bit higher on the temperature.  I have been told that 900 degrees gives you a black color, which I don't want.  I may raise the temperature another 50 degrees on a subsequent run just to see what happens. 
The major components of my setup include a 2" diameter 50" long piece of black iron pipe wrapped with a 24' length of 1400 degree heat cord.  I have a K type thermocouple in the tube that relays temperature through a SSR (solid state relay) and the PID (proportional–integral–derivative) controller.  I am using commercial hardwood charcoal that I broke up into smaller chucks about 3/8" or smaller.  The tube is enclosed, (read not sealed as my goal was not to create a small explosion in my shop) so I have no viewing capabilities though that would be pretty cool.  I also have to let the oven cool down to 200 degrees before I can remove the end cap to access the pipe.

Jerry,
I am all ears when you speak.  Can't wait to hear more and compare notes.   

[jerrywh]

 Dave. I ran one test at 800° F. For about 4 hours on a highly polished barrel.  It came out like a S&W
 Black blue job. Looked like black porcelain.   Not trying to rob your post here. Just wanted to help if I can.    I also scrubbed one barrel with lime before blueing. It would not blue at all. The lime seemed to act as a flux.

[Curtis]

Way cool test, Dave!  Great job of documenting the process.  I wonder if a barrel might blue a little quicker than a solid bar because of the reduced mass?

Curtis

[stubshaft]

Very interesting and educational.  Thank you for sharing.

[heinz]

David, did you clean the barrel between passes or was the color building on what was there before?  Might mean a longer soak time if you were building on the established oxide. 
Great setup and observations.

[Greg Pennell]

David, you might try these folks for granulated wood charcoal. 

https://www.foyspigeonsupplies.com/pigeon-grit-feed-grains/7003-granulated-charcoal-3-lbs

I’ve used this for over 10 years for color case hardening, mixed with bone charcoal in various ratios. It’s typically very clean, and not too dusty, and sure beats crushing up larger grillin’ charcoal.

I have not tried it (yet) for charcoal blue, but it’s on the list.

Greg

[David Rase]

David, did you clean the barrel between passes or was the color building on what was there before?  Might mean a longer soak time if you were building on the established oxide. 
Great setup and observations.

Heinz,
I wanted to examine the effects of both so after the initial bluing of the entire barrel, I draw filed every other flat prior to the next run.  That way I could see the results of both bare metal as well as a second heat cycle on existing blue.  For the next run I draw filed the four flats that we not previously draw filed.  Today I am bluing an entire barrel that a friend brought over last night.  Stay tuned for more results later tonight. 
On a side note, I will be presenting a much more in depth analysis of my studies, as well as a hands on demonstration at the 2018 Montana Historical Gunmakers Guild annual meeting in August. 
David

[David Rase]

Way cool test, Dave!  Great job of documenting the process.  I wonder if a barrel might blue a little quicker than a solid bar because of the reduced mass?

Curtis

Thanks for the observation.  That was my thoughts exactly on the solid bar stock.  I did achieve better results, though not good, with an actual barrel at the shorter soak time.  I just might put that solid hex stock back in the oven for a 3 or 4 hour soak, for the sake of science, and see what happens. 
David

[David Rase]

David, you might try these folks for granulated wood charcoal. 

https://www.foyspigeonsupplies.com/pigeon-grit-feed-grains/7003-granulated-charcoal-3-lbs

I’ve used this for over 10 years for color case hardening, mixed with bone charcoal in various ratios. It’s typically very clean, and not too dusty, and sure beats crushing up larger grillin’ charcoal.

I have not tried it (yet) for charcoal blue, but it’s on the list.

Greg

Is the layer of charcoal dust in my shop that obvious?    When I broke down the hardwood charcoal into smaller granulations I set a box fan to my left so it would blow any charcoal dust rom my breathing area vs. wearing a respirator.  The idea worked great to keep my lungs clean.  The only mistake was that I only had the fan on low so all the dust settled on equipment in my shop about 3 feet away.  I should of used the charcoal I get from Brownell's to do color case hardening.  I would of involved much less cleanup. 
David

[SingleMalt]

David, you might try these folks for granulated wood charcoal. 

https://www.foyspigeonsupplies.com/pigeon-grit-feed-grains/7003-granulated-charcoal-3-lbs

I’ve used this for over 10 years for color case hardening, mixed with bone charcoal in various ratios. It’s typically very clean, and not too dusty, and sure beats crushing up larger grillin’ charcoal.

I have not tried it (yet) for charcoal blue, but it’s on the list.

Greg

Thanks for posting that.  I want to try charcoal bluing in a pipe similar to that Curtis has done.  I've used grilling pure charcoal in an open top box for over 10 years with good results.

David, I take it you're heating your oven electrically.  Could you post either photos or a description of the construction of it?

[PPatch]

ach so, Herr Rase is now our newest mad scientist I see. Nice setup Dave, I will be following your thread with interest.

dave

[David Rase]

ach so, Herr Rase is now our newest mad scientist I see. Nice setup Dave, I will be following your thread with interest.

dave

Just de-energized the controller for run #5.  Due to the good insulation, it should be cool enough to remove the barrel in about 5 hours.  I cooked this barrel for 4 hours.  This barrel is actually going into a friends rifle that he is building for his girlfriend.
Wednesday I will go back to my hex bar and raise the temperature by 50 degrees.
David

[Mark Elliott]

The one charcoal bluing that I attended had the barrel in the charcoal for about 45 minutes total.   The charcoal had turned white and was glowing red inside..   I was told it had to be about 1000F.   It took a long time for the wood fire to get the charcoal container up to temperature, but the actual blueing was quick.       

[David Rase]

Pulled attempt #5 from the oven at 6 pm.  Overall results are not any better soaking for 4 hours vs. 3 hours.  Barrel is a bit darker in color.  This barrel was a Colerain.  The barrel used in tests 2,3 and 4 is a green mountain.  Don't know if that makes any difference or not.  Had a bit of inconsistency in color about 6" from the muzzle.  Not sure if this was caused by maybe my larger chunks of wood charcoal getting hung up at the rear sight when I was pouring charcoal down the tube leaving a pocket or not.  As stated in my last post, I am going to test my 12L14 hex bar at 850 degrees on Wednesday.

[B.Barker]

Thanks for posting all the info you have learned Dave. I wonder if altitude and humidity would makes noticeable changes to your process.

[Eric Kettenburg]

Dave I really think you need to go higher temperature, although the caveat here is that the blue you are seeking may not be the blue I would be seeking.  The way Mark described it above is exactly what I do and I end up with a very 'heavy' looking blue, basically looks like a coating of forge scale but fairly evenly coating the barrel.  Mine aren't perfect, there might be a blotch or change in color here or there, but it's a very tough coating of a dark blue that almost looks like it's on the metal rather than in it.  Think of how a parkerized finish looks - it's kind of like that, but blue.  I am pretty positive the barrel is hitting at least 1000 degrees if not a small amount hotter.  Your bluing looks good, but it looks very different than what I get; it looks more delicate and more "in the metal," kind of like a bright spring blue which can be pretty fleeting.  This is hard to put into words.

I'm not sure the length of time at heat is the primary catalyst here to create the desired appearance, I think it's the temperature.

[David Rase]

Eric,
I think you are correct about the temperature needing to be higher.  Today I cooked my barrel at 850 degrees and the color was remarkably darker as well as bolder.  The picture does not really show a good comparison due to the shop lighting but the top barrel is 750 degrees and the bottom 850 degrees.  Same time in the oven.  Tomorrow I will give 900 degrees a shot, maybe higher.  My heat tape is rated up to 1400 degrees so no worries about electrical failure at 900 to 1000 degrees.
David

[David Rase]

Eric, thanks for coaxing me to go up to a higher heat.  I think I found the sweet spot.  Just pulled a barrel out of the oven that I heated to 900 degrees f.  Left it at heat for 3 hours.  Nice dark fairly even blue.  I just put another one in that I will shut the oven off at 1010 tonight.  I think I will stop at 900 degrees f. for a while.  Might try a higher heat later down the road.
David

Lower barrel after 3 hours at 900 degrees f.  Upper barrel was at 800 degrees f. for 3 hours.