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

If you Nitre Blue but run the temp of the Nitre salts up to 830/850F,,you will get the (near) same deep blue/black color as that of charcoal blueing.
Actually the color will look closer to that done with the American Gas Furnace rotary furnace method.
True Charcoal blue has a slightly 'bluer' tone. But steel type, polish and who's doing the actual bluing all come into play just as in any finishing work.

Don't take the temp much above 850F.
Don't get it near 900F or you'll get a grey color on the parts and that'll be the end of that for the parts as far as coloring them.
You'll have to pull them out, allow to cool. Then re-polish and start again.
That grey color happens just before the steel starts to turn red (heat). That red heat point is right around or at 900F I figure from the mistakes I've made.!

I've mentioned the use of the high-temp Nitre salts a few times, maybe here and other Forums. Never got much response about it.

Like the lower temp Nitre Bluing done at the 650F range, the higher the polish,,the brighter the 'Blue'.
Don't be shy about a high polish. But a sloppy polish won't be hidden by this blue or any other.

This process can be incredibly dangerous as you now have a big container of Sodium Nitrate at 850F and you must keep it at that temp of 850F through the entire bluing time.
Keep any moisture far away,,just like when casting lead. Very explosive reaction.
Safety measures/clothing/eye protection. Even then this stuff if it ends up on you will burn through most anything you can wear and then burn down into your skin.
Anything in your eye,,your eye is gone.

It's hotter than lead is during bullet casting & the quantity can be a lot more when you want to immerse long parts like straight grip trigger guards and bolt rifle triggerguard/magazines completely in it. The parts must not touch the sides of the container. They can hang from wire.

It can take a big heat source to get you there and keep you there.

Smaller parts like latches, sights, screws, ect can be more easily & safely done in a smaller container.
I used to do some restoration parts that way after using the same bath at a lower temp to either spring temper and/or common Nitre Blue some parts that I could do at the same time.

Good comments. Never tried the higher temperature. Heat source limited to about 700°F.
Use nitre fertilizer from the garden store, Goodwill stainless pot and a lead thermometer.
Nice blue on screws, etc. and the most reliable way to temper springs.
Chuck

Thanks Kutter. I have some small parts that can easily be held in a 20# lead pot. I may have to give this a go.

Nitre fertilizer? Really? I'm not sure what that is. I see lots of fertilizers but they all contain a lot of other things as well.

If you are worried about moisture in an action or other part that you are about to plunge into 800+ degree lead (and you should be), you can preheat the part on a hotplate to well over 212F for some period of time to ensure that moisture is gone.

I regularly preheat moulds and ladles for just this reason.

Molten lead scares the bejeebers out of me. Watching those guys on TV heat a knife red hot and then poking it into oil does too...Geo

If no volatiles (water esp) then should be no problem.
I use lead for tempering springs, at 600F

I think the fertilizer thoughts are referring to potassium nitrate, also easily found in stump killer. It’s usually mentioned for nitre blue colors, but might benefit from checking if running up to the carbona black color. Low temperature heat treating salts are easily available and would cover that mid 800* range if the color was just temperature dependent.

Potassium Nitrate should work for this.
I've used it for 'regular' Nitre blue and spring tempering.

We even did some coloring in a certain shop I worked in using Ammonium Nitrate fertilizer melted at high temps to try and mimic AH Fox cyanide case colors.
Not completely successful!, but not a total failure either as far as getting some different colors to appear.
I suspect some other chemical salts were dumped into the mix as well. Shade Tree Science.
It's just plain scary to work around that large of a batch of any of this stuff,,at least for me it is. Too many things can go wrong,,and fast.

Disposing of the entire super heated batch while still liquid was the biggest trick of that operation.
Calling the experiment a failure, but trying to save the large heating pot before the stuff cooled and became a solid mass inside of it.
Very lucky no one got hurt on that one.
It was decided to continue to use Heinzelmann's after that circus act.


As far as getting any moisture off of and out of any parts before they go into the Nitre,,that's something you have to be absolutely sure of. That there IS no moisture involved.
Doesn't matter if you're are working with the stuff at 650F or 850. The results will be the same and not pleasant.

Slowing warming them is the best after a wipe down. All this after a thorough degreasing.
Nitre will not degrease the parts for you. Just like regular bluing, any oil, grease, fingerprints will show in the new blue.
Silicone oil is particularly hard to get rid of. Usually shows up as tiny white specks.

Water...If you warm the steel parts too quickly to make sure they are dry of all moisture you risk having them flash rust in front of your eyes.
Those areas of that very slight rust will not blue or will be off colored reddish, brown or even grey.

The water may also bead up as any excess moisture in a high humidity environment evaporates and as the last tiny bead of water leaves the surface,,a small speck of mineral deposit is left behind.
There's a blemish spot in the new bluing.
Plus usually a halo blemish around it where the water evaporated.

Dry environment, wipe down carefully and inspect.
Then quickly into the Nitre. Don't let parts set around more than an hour or so after final POLISHING as they will start to form an oxide though you can't see it. It will effect the blue and all your work. If they have to sit,,oil them.

When de-oiling and cleaning for bluing,,do it right before the parts go in the Nitre.
When the hot parts come out, they probably will have some nitre on them in places and it will harden to a white coating.
Leave it alone and let the part cool off with the coating on it.
It's still way too hot to put under even the hottest tap water you might have.
There's a real possibility of the stuff splattering yet if hit by water in trying to rinse the excess Nitre from the surfaces of the parts.

Once you do rinse them and inspect them, if you find some blemishes you can SOMETIMES touch up the areas and place them back into the Nitre after cleaning and making sure that all the WATER is once again removed.

Sometimes this re-Nitre attempt doesn't work and you are forced to let them cool,,strip the old finish, repolish, touch up and engraving if necessary and then go again thru the whole operation. Best to do all your parts one time thru and then decide if one or more need any re-bluing

This strip, re-polish and nitre again usually means shutting the Nitre pot down while you do the prep work if you have more than a part or 2 to do.
So a re-start of the pot once again with all the necessary work and time involved.

Like a lead pot,,don't leave the thing un-attended or open to unauthorized persons from possibly getting to it while you are not around such as during it's cool down phase.

Happy Nitre Day

Correct craigd. Ammonium nitrate would decompose explosively at a much lower temperature of 390-400 degrees F. Potassium Nitrate melts at about 633 degrees F and begins to boil at 752 degrees F.

The stump killers and fertilizers are not pure lab grade product, so these temps may not apply exactly. A pot of previously melted salts may erupt explosively when re-melted unless there is a means for pressure to escape.

Kutter,
I've never had flash corrosion from heating too fast. But it is usually convenient to plug in the hot pot you will be heating your PNO3 or your lead pot and, at the same time, plug in your hotplate with the parts on it to be warmed. This is standard bullet casting procedure. The plate heats up gradually and brings the parts up to temperature with it. I do not know how hot my plate is, though I could measure it, if anyone cares to know. I just have it cranked over to 3/4 of max. I also throw a double or triple layer of heavy duty aluminum foil over the mould, part, or tool to be heated. This helps the piece warm evenly.

Doing this with the casting ladle is especially helpful since the grunge on any ladle seems to attract moisture from the air. Heating it minimized the vibration and "boiling" that comes from immersing it deep into the pot for that first helping.

If you have not worked with high temp liquids like this, you just need to be careful and wear only cotton, leather, or maybe wool clothing. NO NYLON BOOTS OR SHOES OR ANY SYNTHETIC CLOTHING! Lead goes through synthetics much faster than a hot knife through butter. A shooting friend dropped a pot of lead on nylon hiking boots with disastrous results.

I have once time poured hot lead into a cold, dusty/dirty Bar ingot mould. The dust and dirt had accumulated some moisture and the mould emptied before it was even close to full. Some lead got thrown around the garage and the lesson was learned. Clean, dry, warm is safe. Everything else is not.

I used to have a low temperature salt setup that was roughly 10 inches deep, and use some stump killer grade potassium nitrate on and off in a different setup. I’d leave a smooth steel rod in it for cooling, a little torch heat on the rod would let it wiggle out of the solid block, leaving a vent hole for reheating.

I just wear full leather welding gear and a full face shield around the stuff when it’s warmed up, no big deal. It doesn’t do unpredictable things. I made a little three hole rack that I could adjust a stop depth on, best control and simplicity for me to anneal rifle brass.

PNO3 ????

I have never heard of Phosphorus Nitrate. If such a chemical existed, it might provide glow-in-the-dark bluing! You learn something new here everyday. Sometimes the thing you learn is that some people who think they are brilliant... really are not.

Seriously...you want to belittle the posts that Kutter provided just because of a typo PN03 instead of KN03 for Potassium Nitrate?

I really enjoy the learning opportunities this site provides from the professionals that contribute.

Not sure of any history here but the comment seem a little over the top.

Scott

DGJ: 98% gold; 2% childish nonsense. I've decided the gold is worth it, but it does get tiresome.

The comment was not directed at Kutter. He did NOT make the error.

DM-You are correct.

Keith-Mea Culpa. I do enjoy the gunsmthing advice you give.

Scott

Some very good points from Kutter, Brent and others. One more thing to never do, with lead ........ if you leave a substantial amount of lead in your pot to cool down and solidify. Next time you heat it back up the lead will begin to melt at the bottom. There will be a layer of solidified lead on the surface that will lead you to wonder if your pot is getting hot enough. It will be the last to melt. Never use an object to break that crust to "hurry things along". I once did, using a sharp, pointed awl. When the point broke through the crust a geyser of molten lead spewed upwards out of the hole made by the awl. Only because of a quick reaction did I narrowly escape a serious burn. Lesson learned .......... patience is a virtue. From what keith wrote it sounds as if this same thing could happen with nitrates.

Great idea of Craig's about the steel rod.

Best, SRH

If I remember correctly, I picked up some Gordon's Stump killer. There were two varieties of Gordon's, one indicated it was 100% pure Potassium Nitrate, the other was Potassium Nitrate with some other ingredients. I used the 100% Gordon's. It seemed to work well on some pins and a trigger guard I nitre blued.

I used a propane burner a stainless pot I picked up at goodwill and a BBQ thermometer that registered 700 degrees. My thought at the time was I need to pick up a better thermometer that registers a bit higher temp.

A bit of a learning curve and I didn't do enough nitre bluing to gain good consistent results for the fire blue I was attempting to get. I did get some nice blue and blacks but it was inconsistent!

Get a Lyman casting thermometer. They are quite inexpensive and very functional.

Inspired by PhysDoc's experiments in charcoal bluing, I thought I would try mimicking it in a lead pot. This thread makes the process sound like it is totally temperature driven and not a chemical process like rust bluing. That begs the question, exactly what IS the chemical nature of charcoal blue, but I skipped past that to try the lead pot.

In my 20# Waage pot, I normally cast at 800 F (measured with a Lyman casting thermometer). Its thermostat is nearly maxed out at that temp, but I was worried about getting into forbidden territory above 900F so, I figured it might suffice. I set up in the driveway to be a little safer with fumes.

The pot got to just under 900F. About 880F or a titch higher. That's as high as I was willing to go.

I had two pieces of dovetail filler bar that I had polished quickly to 1000 grit. I cleaned those in Acetone and deliberately placed a finger print on each of them.

I wired the pieces to some soft iron wire and sunk them in the pot. This could have been thought out a bit better, but it worked.

After 10 minutes, I pulled one piece. As it came up through the surface, it collected some dross that did not shake off or knock off as I anticipated (as lead will flake off a mould's sprue plate). I fetched a wire brush, but it would not rub off very well either by that point. I plunged it back in the pot with the first piece still in there. At the 20 minute mark, I pulled both, but this time I carefully cleared the surface of the lead first and I immediately rubbed the parts down with the brush. This worked much better, but far from good. I would not want a whole action to deal with like this.

Overall, the color was not a deep black but rather a shallow very dark grey/blue. Somewhat mottled and definitely think. It was close, and it was rather attractive, but it was not what I had hoped for. The 1000 grit shine held up pretty well however. There was no trace of either finger print. Both parts were about the same, as the first one was when pulled the at the 10 minute mark. Therefore, I don't think more time is the solution.

In conclusion, I think 880F is not hot enough. Hotter is not a viable solution using lead. The dross problem is another issue.

Perhaps nitre salts would get hot enough and work perfectly, but I suspect there is more to this than heat and that's why they used charcoal in the old days.

Anyway, I hope someone else decides to experiment and finds better results. I'm looking at my grills and wondering how I could make this work.

Brent, don't know. never tried that high a temperature.
With my nitre fertilizer pot, get a nice dark blue on screws and springs at about 700°F.
Lower the temperature to about 600°F to get the pidgon egg blue some people like.
Chuck

Yes, to get the blues, lower temps. I have done that many times in lead and in nitre, but I wasn't looking for blues like that. I was looking for that charcoal color that Fred got. I did not quite get there. As far as I'm concerned, I won't get there with lead. Maybe nitre, but I suspect, it will have to be the right way - with charcoal. No shortcuts.

You get a nice black in niter salts at about 825 degrees, I think 880 is too hot.
Steve

If the goal is to put a final finish on an entire action, a decision should be made ahead of time on the preference to retain any hardness that was present and considered desirable.

Steve, I'll back down and give that a try.

It is worth noting that a highly polished mould sprue plate turns pretty nicely black and it certainly never gets to even 800F, but it takes a long time.