Carbonia Bluing at Winchester

[DWalt]

I suppose most are aware that S&W used the Carbonia bluing process for many years. Yesterday, I purchased a very interesting book by Roger Rule entitled "The Rifleman's Rifle" (1996). It provides a detailed treatment of the history of the development and manufacture of the Winchester Model 70 rifle and all its variations, and obviously was intended as an authoritative guide for the advanced Model 70 collector. It contains a discussion of the metal finishing procedures used by Winchester. What I did not know was that the early Model 70s (1936-39) had their action components (receiver body, bolt handle, trigger guard, etc.) finished by using the Carbonia (or Carbonium) gas oven bluing process, apparently much like what S&W did. A detailed discussion is provided as to how it was done - labor intensive and very time consuming. I can see why Winchester quit using it. It was replaced by the alkaline hot dip black oxide method which most gun manufacturers use today. The earlier Model 70 barrels were rust blued using hydrochloric acid and steam, and that procedure is also explained in some detail. It was also replaced at about the same time by the more modern alkaline hot dip black oxide bluing method.

 

[2152hq]

Smith&Wesson, Winchester, Colt, ,,they all used the American Gas Furnace Co proprietary Carbona Oil bluing system (rotary furnace).
I believe Savage did also.

It was also used in other industries to blue metal parts.
Remember when most small fasteners and hardware were 'blued'.
That were often done in bulk early on in those Amer Gas Furnace operations. They often just used a cheap oil like linseed or other product and skipped the need to buy the expensive propietary Carbona Oil from the Manufacturer of the furnaces.
The gun mfg'rs did the same thing when using the system to blue small parts like screws, pins, plungers, ect in bulk.

They all used the open hearth charcoal bluing method prior to switching over to the quicker mechanized Carbona Oil method.
This would have been in the 1800's and into the first decade of the 20th century.
The results are nearly the same, but side by side you can see a slight difference.

Colt switched in late 1911 or early 1912. The very first 1911 semiauto pistols were charcoal blued. Then they went to the Amer Gas Furnace method.
Those beautiful deep blue early '03autos, early SAA's and DA revolvers made before about 1911 have charcoal blued finish on them. Not Carbona Blue.

Winchester the same thing.
Winchester dropped the Carbona Blue/Amer Gas Furnace process in late '38/or 1939 in favor of DuLite. A hot salt bluing method that's still a popular mix to this day.

Rifle Bbls were generally rust blued in the charcoal and carbona blue era. As were magazine tubes.
Single bbls from shotguns as well.
These all went to DuLite blue when that process was adapted by the factorys.

SxS bbls remained rust blued as the Dulite and most any hot salt blue soln will break down the alloy bond betw the lead and tin in the
solder used to attach the ribs.

Carbona Blue was sometimes a difficult process to get to color match parts of differing heat treat. Dulite/hot salt is a bit easier to control in that.

Charcoal blue and Carbona Blue wear quite differently than hot salt blue.
They both have a tendency to flake off the surface as they wear. It's very noticable when you handle certain fireams.
The Winchester L/A frames are one example where it can be seen easily. In fact the frames were not especially great at accepting the blue in the first place and many wore that bluing right off while the rustblued bbl and tube remain in near perfect condition yet. Just a difference in steel type and probably heat treat or lack of it.

Then there's Nitre Blue,,that's entirely different again.

 

[DWalt]

I had been aware that Winchester went to the Du-Lite black oxide bluing method just prior to WWII. Their method was a little different in that they used two Du-Lite bluing tanks held at different temperatures in succession. 30 minutes at 295-300 deg F., followed by a water rinse, then another 30 minutes in the second tank at 305-310 deg F. Both Ned Schwing's book on Winchester slide action rifles and Rule's Model 70 book agree on that point. Rule says Winchester later went to 20 minutes and 20 minutes.

Bluing tank temperature is controlled by the concentration of bluing salts in solution, not how the heating source (usually gas) is controlled. Higher salts concentration causes boiling at a higher temperature, so either salts or water is added to change the bath temperature up or down, not by adjusting the gas.

"That were often done in bulk early on in those Amer Gas Furnace operations. They often just used a cheap oil like linseed or other product and skipped the need to buy the expensive proprietary Carbona Oil from the manufacturer of the furnaces."

Rule says that Winchester used sperm oil for Carbonia bluing, obtained from the heads of whales. Might be tough to find any of that today.

 

[mauser9]

Great and interesting posts. Heard they don't use these methods these days because of cost or laws against using certain chemicals in the bluing process. All my blued guns are from early 80s and bluing has stood up very well through usage. Do have a Ruger American rimfire with the black oxide satin finish. Don't know how durable compared to the earlier finishes though. Thanks for bringing up this topic DWalt.

 

[DWalt]

So far as I know, there are no environmental restrictions to prevent the use of black oxide bluing solutions. I think that wastewaters resulting from black oxide bluing are subject to EPA categorical wastewater pretreatment requirements for metal finishing, i.e., they must be treated prior to discharge into a municipal wastewater treatment system. But that is not a big deal. Many industrial wastewater sources require categorical wastewater discharge permits. See: Metal Finishing Effluent Guidelines | Effluent Guidelines | US EPA

 

[vonn]

Interesting topic on what is a little science ,a little elbow grease , and a little magic.

 

[mauser9]

Well I certainly enjoyed the read. Many guns today with a matte bluing finish I notice. I have a Remington 700 rifle bought back in 84 which has a mirror like high polish blue. Probably a rust-blue job back then or carbonia type bluing? These days if it's a cheaper process beware.

 

[2152hq]

The Remington blued at the factory in '84 was most likely a hot salt bluing process. and a good chance done with DuLite brand bluing salts.

The mirror brite look comes from the polishing done before the bluing.

Rust bluing will often etch the surface as you go through the several passes or cycles to build up the color. Each one is a very fine rust coating.
If done correctly, you can avoid the etching and you can get just as high a mirror shine w/a rust blue as you can with a Charcoal blue, Carbona Blue or Hot Salt.
It's more work of course. But those high gloss blue bbl's on the top tier Brit and some Belgian guns didn't get there by a dunking in a salt tank.

Technique in application has much to do with it. The soln itself, how it's applied, rusting times, humidity and temp. Even the carding material used and how it's used.

Hot Salt Blue elliminated all that fuss and allowed bluing of large quantities of parts all at once.
You are only challanged by the size of your bluing tank(s) and the capabilities of keeping them at the right temps and abilities to load and unload them.
The factories have huge bluing tanks that take screened tanks with hundreds of parts at a time. The 'baskets' are lowered and lifted by chainfalls & electric winches from one tank to another. There are several tanks involved to hold soln's for cleaning, hot and cold rinse and the bluing salts themselves.
But it's all the same idea as the person with a simple setup in the garage doing a couple guns at a time.

One of the 'tricks' used to get the color to match better in hot blue is to raise the temp in the bluing soln with the parts in there to certain degree. Hold it there for a selected time/minutes. Then some bring the parts out and actually quench them in cool plain water and back into the tank and the regular temp.
Some simply lower the salts temp back to where they are supposed to run.
Different alloys respond a bit different to the processes and there's always an experimenter around to try something to beat the problem(s).
At least w/hot salt bluing you can see the results good or bad as you try them.
Experimenting with Carbonia blue type operations, you have to wait for the cycle to end (about 2 hrs) and the drum to cool before you open 'er up and see what you have.

We tried to find what Carbonia Oil was in real life from Mobil Chemical who had a research facility near by.
They couldn't come up with much other than an extremely thick gear type lube (Mobil product) of which they donated a 5gal bucket to us and said have a good time.
It worked eventually, but as they found out back in the day,,so did Linseed and just about any other 'oil'.
I think I read somewhere that Winchester used Pine pitch or at least tried it. Why not when pinching pennies like they often did.

One of the tricks of the Gas Furnace process was to first drive any moisture out of both the oil and the 'char' being used inside the drum.
(The char needed to be Bone Char,,wouldn't work well at all with wood char,,at least that's what we found)
Simply blending the oil into the bone char and gently warming it for a hour or more would do the trick. A small can of the mix simple sat on top of one of the casecoloring ovens to get nice and warm,,sometimes a little too warm!

Anyway, sperm oil/whale oil was used in the earlier Charcoal Bluing process quite often. Remembering that this process dates from the early 1800's,,probably before that and used in the industry up till the Gas Furnaces took over in the first decade of the 20th Century.
WhaleOil was very common & cheap. It was used for so many things.
I think it was used as transmission oil before we had 'transmission oil'.
Parts would be pulled from the wood charcoal embers, rubbed down with a coating of whaleoil and back into the pit and covered. Inbtw the oil coats, the parts get a rubdown with chalk or other soft burnishing powder.

The processes of charcoal blue and GasFurnace blue are about the same. Temp (850F), ingredients, how it works, ect. One is just the mechanized form of the other.
But they were both labor intensive in their own right. The latter a big improvement over the Charcoal openhearth method though.

The hotsalt blue method top them both and remains the quickest and cheapest method for that type of finish.
Even that has a downside these days with EPA regs the way they are.
Yes you have to properly dispose of any water used in the hot salt process,,even rinse water, to EPA and State regs.
The salts mfg'r and their distributors generally offer a neutralizing kit of chemicals w/instructions for the salt soln when you are done with it. It's safe to simple go down the drain at that point IIRC.
The salts do deplete after a while so mixing a new batch and getting rid of the old stuff is something to take into consideration.
Pouring stuff like that down the drain or venting the 'bluing room' with simple fans to the outside will get you big time fines.
We saw that first hand in one well known shop.

 

[diyj98]

Well I certainly enjoyed the read. Many guns today with a matte bluing finish I notice. I have a Remington 700 rifle bought back in 84 which has a mirror like high polish blue. Probably a rust-blue job back then or carbonia type bluing? These days if it's a cheaper process beware.

That mirror blue comes mostly from the metal preparation before the blueing process. You have to highly polish your metal to get that final shiny finish.

 

[mauser9]

Many thanks to the both of you for the education! I knew polishing was involved but the different "bluing" techniques from past to present is often confusing. For a gun I paid less than $350 for new back then looks kinda custom with walnut and overall finish. Thanks again for all the info.

 

[DWalt]

As there seems to be interest in the Carbonia process (as used by Winchester), I will provide what Rule said in his book about carbonia bluing of Model 70 actions:

"In the carbonium process charred sifted animal bone, resembling corn meal in texture, was poured in a long, rotating cylinder oven. Gas fired from underneath, this was brought to 450 (degrees F); when it reached this temperature, a sampling of the heated bone was removed and mixed with sperm oil. This mixture was then placed in the oven, covered, and allowed to heat for approximately one hour. After thorough fusion, the temperature was stabilized at 490 (degrees F.) and the metal parts to be blued were inserted. Receivers were usually sorted eight to a rack and blued three racks at a time. After the parts were added (to the oven) the temperature was gradually increased to 690 for five hours, which created a mass of smoke. Following this the heat was leveled to 490, the components removed, quenched in oil, and hung up to dry."

Obviously there are some essential details missing, but I don't know any more than that above. I thought I had found a website that would provide more information, but when I tried to get there, it was no longer active. My main question concerns how the parts to be blued are fixed in the oven and do they actually come into contact with the hot bone meal and oil or are they just exposed to the vapors (or "mass of smoke")? I found that sperm oil is mainly a type of natural wax produced by whales (a single whale can produce up to about 2000 liters of it), and wondered if other natural waxes, such as carnauba (plant based), would also work,as sperm oil is no longer legally available in most countries.

 

[2152hq]

The parts actually come in contact with the char/oil mix as the drum revolves slowly. The parts are wired to racks and the racks fit inside the drum and are locked into position inside there.

Inside the drum (the rotating furnace) there are paddles along the sides much like a cement mixer. These paddles pick up, lift and gently drop the char mix over the parts as they too are rotating inside.
The char mix transfers the correct heat to the parts and lightly burnishes them as the stuff drops over the parts and runs off.
Remember the Charcoal Open Hearth system in my other post where the parts were plucked from the charcoal embers and lightly rubbed down with powdered chalk or other fine powder to burnish and even up the color??,,that revolving drum is using the char mix to do the same thing while it revolves.

I'd guess the temp might be a little low in Rules' account. More like 830/850F to get a charcoal or Carbona Blue in any I've worked with.
But I have seen other accounts written where temps in the 450F range were spoken of. But those 450F temps are only in the soft solder range and won't even but a tinge of color onto steel in the open air, nor the char or oil to start to smoke. At least I never could.

Regardless,,the smoke generated by the oil in the char mix has two jobs.
One is to drive any air (free oxygen) out of the drum so you don't get uneven and 'off' colors. Shades of red usually result as well as unblued areas if air is leaking back in and the drum is not sealed.
White specks are generally oil left on the surface. Gotta be clean.
A very small port is located on the drum for the smoke to escape and drive out any air inside and not allow any air from the outside back in.

That initial heat up spoken of is the driving off of moisture from the char and oil mix. The same thing we did in a separate container pre-bluing.

The other thing the smoke from the char/oil mix does is it imparts the actual bluing and seems to determine the actual color or tine to some degree.
The blue is an oxide build up on the surface though only a couple 10th's thick. It is formed in an O2 free atmosphere much like Nitre bluing is.

Using a different oil in the Gas Furnace method will ever so slightly change the blue color on the steel. But so will different steel alloys, and degree of heat treat within the same alloy produce a different color.
This is what Winchester had probl with on the M42 pump. The side plates were not matching the frames. On the Model 21, the frames would flake and wear easily, the trigger plate would retain the bluing very well.
The parts on the respective guns were made of the the same alloys steels, but were heat treated differently. Or in the case of the 21, the trigger plate not at all,,very soft.

All those mix and match color problems went away when Win went to DuLite hot salt bluing in 38/'39.

BTW, a good looking Carbona Blue can be done with Nitre Blue Salts done at 830/850F. (Nitre Blue (sky blue) is usually done in the 650/700 +/- range and on small accent parts like screws, pins and such))
But it's pretty much restricted to the small(er) parts with the quantity of Nitre Salts needed.
When trying to push a large batch of salts to that temp, the heat source must be very intense.
The molten Nitre (sodium nitrate, or potassium nitrate,,either can work) is a real danger in that large enough quantity to do frames and such.

 

[DWalt]

One would think that purging the oven with nitrogen (or possibly carbon dioxide) during operation might help to prevent any problems associated with oxygen presence.

Regarding black oxide bluing salts, the ingredients are fairly simple - about two-thirds sodium hydroxide and one-third sodium or potassium nitrate and nitrite. Some of the older gunsmithing manuals provide home brew formulas for it. Back when I was bluing a lot, we just used the Brownell's salts.

 

[2152hq]

Purging the drum of outside air is a key to the process.
They did it by letting the smoke from the char/oil mix push it out thru a very small vent.
The drum was rotating so the method couldn't have been simpler. It needs to continue through out the entire bluing cycle which lasts about 2hrs.
No need for any kind of flexible hookup to pump an inert gas into the drum. Simple then (1910),,simple now.
,,and no wory that the introduction of another ingredient onto the drum might upset the bluing process.
I don't think anyone really understands what goes on as far as the bluing process is concerned. Yes it is an oxide coating. But why and how does the different type of oil change the color ever so slightly. Why does bone char work and wood char does not (nearly as well) and a dozen other whys.
Then you can, with some practice, get the same result in an open pile of glowing charcoal embers free of draft. There are lots of similarities betw the two methods but yet some that are not.
Temp seems to be one that stays the same.

Springfield Arsenal used a slightly modified method for a while to 'charcoal blue' small parts. They applied a thin coating of Linseed or sometimes Whale Oil to the highly polished parts (like bbl bands and the like).
The oiled parts were then coated with hard wood ashes. Very specific that Hardwood ashes be used but no species noted. Not charcoal,,ashes.

The parts were then heated to the 830F to produce the blued finish on the parts. I'll assume the heating was en-masse in an ovven/furnace set up and not by a direct flame.
Same temp again. The oil is present, the char this time in the form of ashes though. Smoke must be present during the heating to drive off atmosphere around the parts. No mention of burnishing the parts down by hand during the heating as with open hearth charcoal bluing as done at Colts and others.
Just another way to get a Blue/Black oxide finish on steel.

European gunsmiths for years 'blacked; trigger guards and other small steel furniture on their guns in simple open crucibles or pans of charcoal.
Bury them in the coals, take them out after a time and burnish them down with thistle or hemp, the parts dusted with lime or chalk. Some oiled them lightly others not and placed them back in the coals and covered them back up.
Most hardwood charcoal glows at 830/850F. Don't intro any draft to it and it stays at that temp. There's that same heat temp again.
The same idea as the open hearth charcoal bluing method only on a small scale.
Several cycles produces a deep blue/black oxide coating.

I think Parker and few other US makers used the process too on trigger guards and some hardware at least early on. It has a distinctive look over Nitre blue and Rust blue for sure.

Home brew hot salt bluing salts recipes are well known,,and they work just fine. Many have used them to complete satisfaction.
When it was easy to by Lye (sodium Hydroxide) off the shelf in most any grocery store or hardware store (Red Devil!) it was easy to make up the stuff and no one paid much attention.
But now that is gone from the shelves in plain form and buying a 15 or 20 lbs of sodium or potassium nitrate catches more than raised eyebrow look these days, not so easy anymore.
IIRC it takes something like 8#(?) total of the different salts dissolved into 1 gal of water.

You'll need about 4 gal of soln to blue long gun bbls, so there's 32lbs of a combination of lye and sodium/potassium nitrate.
Shallower tank you can get away with less soln. But you don't want to skimp too much and chance boiling dry. You are working at 300F range so things can change quickly.
Much less soln of course to do pistols and small parts in a small tank.

For small parts and pistol frames,ect, I used to use a 50cal ammo can as a bluing tank. Worked well for what little hot blue I needed.
When done and it cooled off, I put the ammo can lid back on with it's rubber seal and it kept the salts from dragging water out of the air which they will do.
I did have a tank set up for long guns for a short time but used it very little. It became more of a pain than a blessing. Took up lots of room, was messy and got little use out of it. I didn't want to become a 'rebluer'. Just needed the apparatus & ability for my restorations. Hot blue was not at the top of the list for that.
So I tore than down. I only use one 45" stainless tank now for rust bluing long gun bbls and a small tank for the little parts..



Commercial mixed salts from Brownells is certainly available, has been for years as has Dulite and a few others (HeatBath was on the market for quite a while, maybe still is).
They sell in quantity. Shipping is costly. But if you are in the biz, it's probably the way to go.
Some say Brownells salts produce a Blacker finish than DuLite, others disagree. Polishing and technique in use has a lot to do with the final appearance as well as what the steel alloy is.

The shops I worked in usually used Brownells salts though one used Dulite.
One shop chose to mix his own salts and it worked well. When he decided to add Potassium Cyanide to the salts so he could hot salt blue soft soldered assembly SxS bbls,,I decided to skip trips to the bluing shack.
The factorys both used Dulite. Most did.

Dulite was the standard of the industry and about the only US compound around when Hot Salt bluing took over the gun blue finishing in the late 30's.
There were a couple German hot salt blue compounds already in use but they weren't going to appear here in the US gun industry in 1939.
Some US gunsmiths and shops used the stuff and had been for a while.
Hot salt bluing was well on it's way by the mid 30's.

 

[DWalt]

Hubbard-Hall offered (and still sells) an oxide bluing salt product they called "Black Magic", which is very similar to Du-Lite. Seems to me it was probably used by S&W at least on some Victory revolvers, as S&W referred to the use of Black Magic. Here is a little video from H-H about how the oxide bluing operations are performed. Black Magic | Hubbard Hall

 

[Blind Boy]

This is a very interesting thread subject. Blueing and browning are fascinating. I thank you all for your participation and dissemination of knowledge.