charcoal bluing again.

[jerrywh]

 I suspect that Tom Snyder doesn't know any more than has been revealed on this forum. The heat it takes to develop that heavy oxide blue is over 1000° f.  It will warp a barrel if the barrel is not bedded well or it is heated unevenly or cooled too rapidly. I know this for a fact.  I had the Historical arms making tech books for years and they never did come up with a method to eliminate the blotching of the blue of either process. It is supposed to look like this only a slightly different shade of blue. Acer blued his with a torch.

[Curtis]

At the NMLRA Gunsmithing Seminar in Bowling Green KY this June there is supposed to be a demonstration of charcoal bluing.  I'm not sure who is demonstrating, and have no idea what the process will be...  but if it takes place as planned I will be happy to relay the details as well as the results.  It will be an educational experience regardless!

Curtis

[bob in the woods]

That's the same look/finish I got on my Chambers Officer's Fusil.  

[kutter]

Just some random thoughts from my experiences in restoration work

Run some Nitre Blue salts up to betw 800F and 840F and blue some steel parts in it.
You get nearly the same look as Carbona Blue and not that far from that of charcoal blue.

They are all related,  
They are all done in the same temp range of 800F to 840F.
They are all done in the absence of contact with the atmosphere and the oxygen in it.


-We got various shades of blue (reddish tones especially) if any outside O2 got at the parts during Carbona Blue process.
- If packing a part in charcoal that is then heated up and blued and a mottled pattern/look is the finished product. It is very likely due to moisture in the charcoal. That moisture then starts to evaporate from the char as it heats up and causes spotting on the steel surface before it evaporates.
The evaporation pattern on the steel is what then shows through as the mottled blue look to the finished product.
Warming the charcoal just before packing the container will usually take care of it.
Warm the bbl also before packing it in the char.

We got the same problems during case coloring. The moisture in the wood and bone char left marks on the case harden parts that showed under the CCH pattern.

Leaving the next days worth of 'char' in a large,loosely covered steel box on top of one of the furnaces at the end of a day would dry it out sufficiently overnight as the furnace cooled down.

-The oil and bone char used in the Carbonia Blue process was warmed also to drive off any moisture before being used.
-Use real Hard Wood charcoal for any of this stuff. Don't use formed charcoal briquettes as they have binder mixed in to make the neatly formed little blobs and will play havoc with your blue or case color.

FWIW:
One of the old methods of 'charcoal bluing'  small parts,,supposedly Springfield Armory used it at one time but I don't know if that's true:
Coat w/a thin coating of oil, linseed works. I've been told WD40 does too(?),  .
Then dust the part w/charcoal dust (some say hardwood ashes work but I've gotten little luck with them).

Mark the part in a small inconspicuous area by simply rubbing a small area free of the dust & oil w/your finger tip so you can see the metal for color change.
Heat the part and watch the small indicator area for the color change to the blue shade appropriate.
A thermostat controlled furnace is nice for this, but 'by eye'  isn't too hard to do on small stuff.
Let cool & oil.

Some same ideas involved but not much of a set-up required. Works good for trigger guards and small parts if you can control the heat evenly over the entire part.

[Tmas]

Curtis:

Is it possible to get a more uniform color on the rifle you posted by oiling it and rubbing it down with steel wool or a polishing compound.  The dark spots seem to shine, like they are thicker. 

Jerrywh:

That double looks very good.  I would be happy with a finished that color.

[jerrywh]

 The double barrels are actually perfect. The differential or the color in that photo is just fingerprints.
 Those barrels were done in a special furnace or my own design. I also had some advise from Dave Crisalli.
  Kutter. Are you telling me you did carbona bluing? I thought I had about all the info on that in existance now days.

[Long John]

Jerry,

I have a question regarding your shotgun barrels.  The temperatures everyone are quoting are substantially higher than the soldering temperatures commonly suggested for the assembly of the barrels with soft, low-temperature solders.  On your shotgun (which I think is exquisite - but you already know that) did you blue the barrels first and then solder them together?  Will soldering fluxes commonly used for tin/silver "soft" solders achieve wetting if the bluing has not been abrasively removed?  How do you keep the solder from flowing all over and ruining the beautiful blue surface?  Do you use some form of "solder mask" to limit the solderable area when joining the barrels?  Your photo triggers a bunch more questions but I don't want to be a pest.

Best Regards,

John Cholin

[jerrywh]

LongJohn.
  I made my own barrels and they are silver soldered together with silvaloy 56.  That is a 56% silver alloy.  The melting temp of 56 is about 1200°F. The ribs, RR thimbles and lugs were all silver soldered at the same time.     I built my own furnace for brazing barrels just for that purpose.   
Acer may have seen this furnace a few years ago in my shop.   I studied how to do this for about a year off and on without warping and causing extreme oxidization inside and out.  They did warp about .010” and I had to straighten them.  There was little or no oxidization inside or outside.  Dave Crisalli helped me figure out the process.   Two of the best shotgun smiths in the country said it couldn’t be done.   I knew it could because the French and Belgians had been doing it for a couple hundred years by a similar process.   They were blued in the same furnace. The furnace is convertible from an enclosed type to a ceramic glass top that you can see into.  The barrels are 32” long with a muzzle wall of .032”.  They were blued after all the gold work  was complete.  You just don’t do that in a bonfire.   I am pretty sure someone in every country in Europe was doing this by the 18th century and before.  I have been studying these processes for at least 20 years off and on.   I have evidence that even rust bluing was done in France about 1800.  Information on bluing in 18th century Europe is hard to find because the guilds kept it secret just a some do today.  Some don’t like all the references to European guns but this is where most of the gun tech in America came from.   It’s not logical to separate the two.   I purchased two tubes from Long hammock barrel co. in Florida and then contoured   them to an 18th century pc shape.  I am positive the bluers of Europe didn’t do it in a fie pit.
    I have photo documented the whole process for a future publication. Maybe. 

[jerrywh]

 Tony Clark.
   If you don't have a pyrometer you don't have any idea what temp you are at.  Everything I do is measured by two or more digital pyrometers. I have four furnaces. One has 6 pyrometers and one has two the others have one.They measure temp to one tenth of a degree F or C. by the color your barrel never went over 600F. If it did that color would have disappeared an it would not come back at any higher heat.  The spots are caused by moisture in the charcoal or impurities. The charcaol produced by an open fire is very impure and there is no way to obtain constant and accurate control. Also you have no control over the oxygen content.
  I don't mean to be combative but that is just a fact. Even the type of wood makes a difference. The resin amount and etc. In order to produce a perfect result on a regular basis everything must be constant. A system can be developed by trial and error but it will take a lot more than one or two trials to do that.

[Long John]

Jerry,

Thank you for your reply.  You have been very generous with your knowledge and I am most grateful. 

I hope you don't mind if I pester you with a couple of other questions via the personal message system here.

Best Regards,

John Cholin

[jerrywh]

 Long john
    You can contact me by Email. Just click on my name and you can get my Email address.

[Eric Kettenburg]

I've had quite a few pieces here that definitely were blued through some form of assumed charcoal process.  Definitely deliberate, because it was on the underside of the barrel and it was done *after* heavy filing and after under lugs were installed - one or two pieces evidenced the blue under old loose dovetails.  It was not only an "early" process either, it's been seen on guns as late as approx. 1810-1815.

I have never found a period or otherwise documentable reference to the process that appears to have been used.  So currently we're all doing it via experimental archaeology. 

The process I've used is essentially the same process Tony has outlined above.  I have no idea what temperature is being reached nor do I care.  All I care about is the end result, which also looks identical to Tony's very pretty work.  So it's all via eyeballing measure for me.  I don't have any problems with it being repeatable.  I do believe the key factors are a deep bed of consistently burning charcoal, so as to severely limit oxygen, and something to cover the bed and keep it from getting away from you.  I use large old steel sheets.  I use a metal trough, probably not a good idea to do it directly in the dirt.

I think the idea of constantly pulling the barrel out and rubbing it down in some way is a bad one.  Early on, tried this and it seemed to promote warping and especially scale buildup.  I do think it is important to very thoroughly degrease the barrel before bluing, and not to touch it until afterward. 

If it's done right, it does not appear as a flaky scale buildup and there should be no need to lap the bore.  And it's tough as nails.

The end results seem to very accurately mimic what I have seen on original American arms as well as some German guns of mid 18th century.  I have not seen the very fine, lighter 'temper' blue on any American guns nor any of the German guns I've had, although I'm sure it was used in Europe probably on higher quality pieces based upon existing arms (none that I've personally had here but pieces I've seen via photos) as well as period description of what seems to be a much more low-temp and quick process.

[crankshaft]

   I will/may try anything once.  I  read it on the interweb it must be true.       .     I once charcoal blued a bbl.   
 Nice even dark  blue.   
 After 25 yrs. of little use it is now a nice brown.

[jerrywh]

Eric Kettenburg
 That is a good idea about putting a sheet of steel under the fire to stop the moisture  and dirt from coming up through.  Thanks for the input. I like your guns a lot.

[Joe S]

Eric

How long do you leave your barrels in the charcoal?

[Curtis]

Curtis:

Is it possible to get a more uniform color on the rifle you posted by oiling it and rubbing it down with steel wool or a polishing compound.  The dark spots seem to shine, like they are thicker. 

TMAS, The thickness of the bluing is very uniform.  The barrel was rubbed down, oiled and waxed several times before the photos were taken.  It does almost have a 3d effect but is is only in the colors.

Curtis

[Tmas]

jerrywh:

Its been quite here. Just wondering how your experiments are doing. 

[jerrywh]

 The method of bluing in a dirt pit full of charcoal was invented or developed by George Suiter at Williamsburg, According to Gary Brumfield. There has never been found any documented evidence that the method was ever used by colonial gunsmiths or anybody in Europe or England. I have yet to see a single specimen that lives up to my standards or the standards of any of the guns done in Europe in the 18th century or earlier. That is how it is without regard to political correctness.  In plain words , that is the unmitigated fact. I spent months doing tests and researching the subject. Also. I have never seen a case where wood charcoal was touching the metal and the blue came out without defects or mottling. Gary Brumfield even had trouble with the bore when he did the high temp process and he had to recut the bore. That could be remedied but the outside surface will still come out mottled and with some flaking.  In my opinion I would never heat a barrel to over 800 deg°f  in that environment.  Eric Kettenberg had the best method in my opinion for doing so. He says he put a sheet of metal between the barrel and the charcoal.
   The term Charcoal Blue only infers that charcoal was somehow evolved in the process.  It does not mean the part was covered or packed in charcoal. The French and Belgians did their bluing over a charcoal brazier.   I have actual evidence to prove that. I have done enough of this to be able to tell that the rest of the European did it in a similar way. I have run at least 25 actual tests an different methods. Getting into even more modern times ,there is documented evidence that even S&W and colt that did a charcoal bluing process never let the charcoal touch the metal parts. I have historic evidence for that. Getting a perfect or even a close to perfect result in a fire pit with the charcoal touching the metal is an impossibility in my opinion. BUT, Perfect to a degree is a matter of opinion. What some people call perfect don't pass my standards. A lot of people don't even want perfection. In conclusion. There is very little or no evidence that the mottled gray blue is historically correct. It is a theory developed by George Suiter. The lower temp bluing is a whole different subject.

[JCKelly]

As you gentlemen are aware, there are two types of blue color which one gets by heating iron or steel.

The first is "temper blue", the color of a polished piece of steel heated to about 550 - 600°F. This really is a clear, colorless film. It makes an "interference film", about the thickness of blue light's wavelength. The colors you see are like those on a puddle of water with a little oil on it.

Huh? Anyway temper colors, straw through blue, are very thin and do not survive much as a metal finish.

Both nitre blue and charcoal blue are actual thick (relatively) layers of Fe3O4. This is the chemistry of scale one finds on steel that has been heated red hot in the forge or torch. Just like metal, oxides have a grain or structure to them. The scale from a forge is dull in color and flakes off easily. But, if you can form that scale in a very, very low oxygen atmosphere it will be thin, fine-grained and adherent. That is a gun barrel blue.

Colt percussion firearms were charcoal blued in a open furnace by skilled workmen. Probably a lot of carbon monoxide, no oxygen to speak of. I recall they rubbed fish oil on the metal during the process. An engraving of the Bluing Operation is shown on page 356 of A History of The Colt Revolver, by Charles Haven and Frank Belden. It was originally published in the  United States Magazine, March, 1857.

I rather doubt that the metal was all that hot, probably under 900°F or so. Perhaps that information is available somewhere?

Charcoal bluing is a process wherein one gets a very thin scale. In the early 20th Century Colt blued in a rotating barrel full of charcoal. That was a mechanized version of how Sam did it a century earlier. Doing this successfully by hand requires a lot of skill. It does not, in this metallugist's most humble opinion, involve heating the metal until it glows.

An industrial process to get the same type of scale is "steam bluing". Back in the 1960's  Black & Decker used steam bluing to get a blue-black color on the shoes of small portable jigsaws. I thought it was at 950°F. It was not pretty, but then no one polished the steel first. It did give some degree of rust prevention. Hardware screws used to be available with this steam-blued finish on them. ThyssenKrupp says the process is done at 840°F (450°C). Their steam has very low oxygen content, about 0.01% oxygen.

By the way, this is the ideal time of year to Google "charcoal bluing". Your rhubarb, and her roses, will love most of what you find.

[rich pierce]

Very helpful information. Good to know that some of what was done at Colonial Willismsburg was experimental archeology of sorts rather than relocation of documented processes. Now I will avoid charcoal blueing.

[Tmas]

Jerrywh, J C Kelly:

Thanks to both of you for your explanations.  I never really felt that a fire pit was the correct approach.  Also, temps over 1000F seemed out of place.

So, is the preferred approach a controlled atmosphere furnace @ 800 to 840F, or nitrite bluing in a similar furnace? Or are we trying to find a way to get what we are looking for, standing in a hammock and should look for something simpler?

BTW;  I have always loved it when real metallurgists showed up and explained all the alchemy we were being fed.

[jerrywh]

The following is a partial quote from a description of the colt bluing process called carbona bluing.  This description coincides with the tests I have conducted. I want to say that bone charcoal and wood charcoal act very differently. Wood charcoal is much worse at spotting when it touches the metal.
This comes from a book called a century of achievement which is a history of the colt revolver.

"What is the chemistry of bluing, anyway? How does this bluing process impart this handsome and lasting blued steel finish so famous on Colt firearms? Bluing is a combination of carbonizing and oxidizing that by heat brings the inherent carbon of the steel through the opened pores to the surface. All the coloring is done by heat; no particle of bone ever touches the parts being blued. The smoke given off by the primer expels free oxygen from the drum leaving only sufficient to allow combustion. The primer and the charge control the composition of gas in the furnace, the heavy carbon dioxide shielding the parts from contact with oxygen. All this calls for expert knowledge and experience in mixing the proper proportions of the primer and charge not only to obtain the proper color but to create a smoke that shall be free from moisture. Otherwise, though being blued, the pieces would be spotted.”
     
Evidence in 18th century books confirms the same thing when it comes to bluing European guns. Look in  Diderot's encyclopedia of trades and industries published about 1750  under the guilders trade and you will see them bluing gun barrels over a charcoal brazier. There are others. Most European guns were heat blued over charcoal and some of them still look pretty good until today.
   My tests confirm what I have said. Browning was mentioned as early as 1632 and I have seen a Boutet gun that was rust blued about 1810.

[James Rogers]

I am very interested in the documentation on 17th century browning and to what material items the process was connected. I have seen the early references to "russetting" barrels (cant remember the exact year) which as I understand some assume was not browning as we are familiar with but a pigmented application.

[Long John]

Jerry,

If we arrange the bluing oven/furnace so the charcoal never touches the gun barrel, how do we keep the barrel from getting blued inside?  Do we fill the barrel with something and plug the bore?

Years ago I had to travel to Europe for work.  On my way home I spent the weekend in Copenhagen and spent an entire day in the Danish National Museum of Weapons I think its called the Tohussemuset or something like that.  I had a crappy camera and flash pictures were not permitted.  But I saw original guns that had brilliantly blued barrels EXACTLY like the shotgun barrels you show above.  Simply stunning!  I also saw guns with what I believe were browned barrels - the browning was almost a garnet color and they were polished as smooth as glass.  Many had gold damascene decoration like your shotgun, above.

I suppose one could make up a steel box, 4 feet long and skinny, maybe 6" by 6", fill the bottom 1/3rd with charcoal, lay a steel plate over top, sit the barrel above the steel plate and then put a nice tight lid on it.  Now the "box" is placed on a heat source to bring the temperature up to the right level.  The temperature can be monitored with a couple of I/C thermocouples and a Fluke DVM.    But what do I do to prevent scale or blue build-up inside the bore? 

Also, if the purpose of the charcoal is primarily to deprive the interior of oxygen, then almost any hydrocarbon would do, wouldn't it?  If you heat a hydrocarbon pyrolyzes to carbon, carbon dioxide and carbon monoxide.  A liquid hydrocarbon like vegetable oil would have no ash contaminants at all.  I know, when I start thinking there's no telling where I'll end-up!

I want to publicly thank you, JCKelly, Eric K. and the others for sharing you knowledge.  I remain in awe of all you guys know!

Best Regards,

John Cholin

[jerrywh]

I want to add this comment. There are still three or four tests that I have not yet run. All the tests that I ran this year and in about 2000 were all done with granulated wood and bone charcoal. The comments I made about spotting apply to those tests.
  
Up to this point I am inclined to believe that the charcoal was used because it was the only large supply of clean heat that was readily available in the 18th century and before and basically all the bluing they did was heat bluing to one extent or another. I do know that some swords were blued in a pile of hot sand over a forge and charcoal was only used to heat the sand. In Diderot one illustration shows a man bluing over a charcoal brazier. There is a pan suspended over the charcoal on bars. I suspect the pan would be copper.   A copper pan would diffuse the heat and make it more possible to obtain a even blue.
  I just gave a class on these things at the Oregon gun makers fair.  When I get home I can post a photo of the Diderot engravings and there I have references to browning in the 1600's
  So far I have no info on the process used because even then the guilds kept everything secretive.
  I agree with Eric in that I have never seen an American gun with the low temp blue. The temper blue or low temp blue was basically for royalty or presentation firearms in Europe and England.