doublegunshop.com - home Forums General Discussion DIY Gunsmithing @ doublegunshop.com Charcoal bluing

I wanted to give charcoal bluing a try, I found this recipe in Clyde Baker's book "Modern Gunsmithing"

It reads:

An old English gun maker gave me the following which I have seen him use to produce very fine work, although I have never used it myself:

Make a boxy of heavy sheet iron large enough to hold the largest part to be blued. It is not necessary to rivet or weld the box, merely fold the corners. Fill it with pulverized wood charcoal in lumps about the size of a small pea, and heat in a furnace or large forge until the charcoal is partly burning throughout, but not quite redhot. Attach an iron rod at least two feet long to the gun, and bury it in the glowing mass, allowing the rod to stick out for handling. In 5 to 10 minutes, lift out and examine it. If the color has started, take a large wad of clean cotton waste or tow, dip it into dry powdered lime and rub vigorously over every part and work fast. You may be fooled at the first bright blue that appears. This is merely a "tempering color" and must be disregarded. It will not wear, and it is not the blue you are after. Continue the treatment until a deep blue-black similar to that seen on Colt revolvers has developed. Let cool in the air (do not quench) then apply any good light gun oil.

Oops this got submitted before I finished it

returning to Clyde Baker's book

The process may be repeated a second time if desired, usually deepening the color. The parts must of course be cleaned of all this by applying a mixture of chalk and water, letting it dry on the gun, then brushing it off.
A variation of this method was at one time used by Smith and Wesson, except that the gun was rubbed with oily waste instead of lime. Either method required considerable skill and experience, but the results fully justify the effort."

I had looked through the internet other discussions of this, and thought I would give it a try at home. I had a trigger guard that I wanted to reblue, a floor plate and a ramped front sight. I polished the portions of the trigger guard and floor plate that I wanted reblued to 600 grit and degreased them in acetone.



I smashed up some charcoal briquettes and put them in an old roasting pan. But that on my gas grill and cranked up the burners to high and waited, my grill may not be the most powerful, I reached a high temperature of 550 F. At that point, the charcoal at the surface was turning to ash and would glow if a breeze hit it. Not quite the description of the coals in Clyde Baker's book. But I gave it a try anyway. I submerged the floorplate and front sight in the charcoal and pushed the bottom of the trigger guard into the charcoal and used a trowel to cover as much of it as I could, the magazine box stood out of the charcoal. Every 15 minutes or so, I would pull the parts out and rub them with a cotton cloth dipped in rottenstone. Here are the results.



The quick release lever was fire blued. I was really pleased with the results, it could be done without much in the way of specialized equipment. I will definitely do it again. Next time, I will wait until I have a number of parts to blue, use more roasting pans and build holders for the parts. I was fishing them out with tongs and holding them with tongs while rubbing them with rottenstone. If the tongs slipped, I would get scratches.

Nice work!

As long as the charcoal starts to consume itself (burns with a white ash),,it'll produce the results you need.
Allowing a draft to fan the coals and boost the temp will result in a grey color and then a heat scale on the the parts.

The deep blue/black color is produced at about 830/850*F.
That just happens to be the temp that wood charcoal burns and consumes itself w/o any further help from an outside heat source.
The occassional scrubb down is a burnishing technique to even out the color and remove any blemishes on the surface.


Scale won't form when it's out in the air being burnished down as the metal temp is below red heat,,or it should be!
(You can get the same blue/black color look if you Nitre Blue and run the temp of the salt bath up the same 830/850F temp.
A lot more dangerous than doing it this way though!)


Imagine doing this over a huge open hearth of burning charcoal all day and with hundreds of parts as Colt, S&W and most every firearms mfg did at one time.
The factorys used child labor to do the work in many instances as it was dangerous but didn't require a high degree of training or skill development over time.

Small parts handles make the job easier as you found so you can scrubb and quickly return the part to the coals. Bury the part and rake coals over the part again and move to the next one. Keep in rotation and you can set a pace with the number of parts you are doing and the size of your set up so you have no down time and the job gets done fairly quickly.
It's still hot work! But the results are so worth it.
Nothing like it for those early SxS trigger guards.

Most modern instructions warn NOT to use charcoal Briquettes as they contain a binder (clay?) and possibly other materials to spoil the finish. You seem to have proven otherwise!.
I've always used small chunk charcoal. Didn't seem to much matter what brand. Some say they use Aquarium charcoal.
I don't know,,It's much like any of the finishing processes. Lots of different ways to get results.
You find one way that works well for you and stick with it.

That looks great Fred. I need to give this process a try.

I believe this is a variation of the Charcoal Blue process that was used by Colt. But in the Colt process, the parts were held stationary in a rotating drum oven. The charcoal was heated along with the parts to the correct temperature. As the drum rotated, the tumbling of the hot charcoal over the steel surfaces provided the burnishing. Another variation was called the Carbonia Blue process, which was used by Smith & Wesson. It also utilized a rotating drum oven, but instead of wood charcoal, they used bone charcoal that was treated with a proprietary product called Carbonia Oil that contained pine tar.

Both of these processes replaced the earlier hot, dirty, and labor intensive hand burnishing described by Kutter

Thanks Kutter and Keith

I really appreciate what you both wrote. After having tried it and then read your comments a lot of things made more sense. It took about 3 hours of work to get the color on the metal and it was initially quite discouraging. But once the charcoal began to consume itself, I noticed a lot more heat coming from the setup and the color appearing more quickly. Thanks Kutter, what you wrote really helped me to understand things. Next time, I will put the stuff in the grill and wait a lot longer before putting the parts in the charcoal and will have specialized handles.

And Keith, thank you, I had read such varying descriptions of charcoal and Carbonia bluing that I wondered if they were talking about the same thing. And I wondered why the rotating drum was necessary. Now having tried it and read your comment, I see how the rotating drum and having the charcoal tumbling over the parts provides the burnishing. That makes sense. Thanks again.

Yes, it is a hot, dirty and labor intensive process, but I could use to sweat off a few pounds. I think also that for the home gunsmith,it is a great technique to try in that it does not require a lot of additional equipment, provided that you have a grill to start with.

I also appreciate the time you took to share the info and experience. Thanks to Kutter for rounding out the process. If Kutter is still following along, I wonder if you've ever engraved on a case hardened surfaced that went through this form of heavy tempering vs a full anneal?

Still here,,

This Charcoal Blue /Open Hearth method is what Colt and others used before the American GAs Furnace Co. method came on the scene.

Colt blued all pistols including the first year Model 1911's with Charcoal Blue.
Then the switch to the Amer Gas Furnace Co. rotating furnace took place. Somewhere in the 1912 time period the change took place.
A mint condition 1911 mfg'd Model 1911 and a 1912 mfg'd Mod 1911 placed side by side will show the very slight but yet noticable difference in the tone/color.
Any other Colts blued on either side of the change in operation will do as well.

Rifle Bbls were always rust blued at colt.
IIRC the only rifle bbl that was charcoal blued in a factory was the Henry rifle bbl. I can't think of another but there probably were others.

S&W changed over to the Amer Gas Furnace system about the same time as Colt. S&W kept theirs running much longer than Colt according to Roy Jinks their historian.
Winchester, who also used the AmerGasFurnace stopped using it and went to HotSalt DuLite just before WW2

The first of the Win21's were blued using the Amer Gas Furnace method. That method of bluing is also using a temp in the 830/850F range.
I've engraved/recut a number of the early 21's that were blued using that method and they seemed to be as tough on the chisels as the later hot blued 21's which didn't see those temps in bluing.
Winchester went to hotsalt blue (300F+ temps) around 1939)

I can't recall engraving any casehardened parts that had been thru this charcoal blue process.

Cutting case hardened steel is kind of odd. Since the 'case' can vary from nearly nothing to a few .000, cutting thru it is more like punching thru it, Getting underneath the hard surface and into the soft steel, the graver goes along quite nicely. Carbide gravers are a near necessity though. HS will just nub over getting through even thin case.

The problems are that the cut you make as you chisel merrily along looks somewhat like plowed furrow.
It doesn't cut cleanly on the surface. The soft steel underneath responds just fine, but that thin glass hard case breaks up in tiny fragments as the upper portion of the tip of your chisel point pushes it's way through.

Also when you come to the end of a cut, you have to dive through the casehardening once again to begin the next one. You do that hundreds if not thousands of times on a pattern. It gets to be laborious trying to get through the case hardening and it's various thicknesses.

Then there is the issue of cutting fine lines. There is almost no way to do that. A light tough such as shading is impossible as you can't get through the case. You can get a scratched surface as the tool skips off the hard case, but that's about it.
Any punch work and you just batter the punches and flatten them to useless spindles.

Thanks Kutter for taking the time to comment. I believe yours is the first deeper explanation I've seen about why an engraver prefers a case hardened part to be annealed. Generally, it's just mentioned as an automatic passing step. I believe there are folks that will engrave, for example, a modern high alloy hardened stainless knife blade, but they probably wouldn't have to contend with the complications of a case.

Back to the topic, I asked about the high temperature anneal, because the usual recommendation is to pack a part in basically the same char coal. But, I'd think that annealing above critical temperature, in that manner, also drives more carbon into the surface of the piece. It may just turn out to indistinguishable, but on the other hand, occasionally parts crack. Thanks again for your comments, and to you again PhysDoc for the inspiration.

Glad to do it, this is what the forum is all about. After trying this, and rereading Clyde Baker's description. I think if he would have tried it, he would have omitted the part about "Either method requires considerable skill and experience" it wasn't that hard to do. Probably by the end of summer, I will have some more parts that I will want to blue this way and will do it again and report on the results.

I've been thinking about this process for a while now and everything that was posted about it sounds like this is just a temperature process. If so, then why not do this in a lead pot or nitre salt bath that is turned up a little higher than one would do for spring tempering? Even if the burnishing is essential, that too, could be done with lead pot or nitre bath. Perhaps it takes more than 900 F? -at which point, I would not want to be messing with lead.

I am considering trying this method with my next projected.

How much shine or gloss does this process allow? About the same as a slow, dilute rust blue or something more?

Brent