Making wood charcoal for color case hardening.

[Rolf]

I used four 2,5 gal paint cans as retorts. I drilled a 8mm (3/8") hole in the lid.  The can was packed with stave's of birch wood. Stave's about 1/2 square worked best.


The retort was fired in a Weber grill. Each burn took 2 hours and produced 1gal of crushed charcoal. Each can lasted two burns. The first all the water steamed out of the wood.


When the water was gone, the oils and waxes were burned off.


Took about a day to make 8 gal of birch charcoal. The retorts were fired in relay. One can in the fire, one can cooling off and one can being filled with wood.




Need to make a sieve for sorting the charcoal. What size should the pieces be for case hardening?

Best regards
Rolf

[JCKelly]

According to Gaddy, 80 mesh wood charcoal has been used, don't know whether that size is best.

To get colors one need maybe 20% or so bone charcoal. A dull & uninteresting way to make bone charcoal is to write an appropriate size check to Ebonex Corp, Melvindale, Michigan. They make the stuff and may be found on the web.

You might want to read the two-part article by Oscar L. Gaddy "The Color Case-hardening of Firearms", The Double Gun Journal, Winter 1986 and Spring 1997.

[jerrywh]

 If bone charcoal is a necessity then why does steel turn blue when heated with anything to 600° F.  I have done a lot of color hardening with no bone charcoal. If hot steel is exposed to oxygen it will turn colors . The design of the colors is determined by the exposure to oxygen through the steam bubbles when it is hot. Plain iron will turn colors also even if it has little carbon content. The charcoal or any organic carbon does two things. When heating it insulates the metal from oxygen and the iron or steel absorbs carbon when in contact with organic carbon.  I don't think it is the carbon type that makes the color because the part will change colors even if you soak it in kitty litter and quench it. If you want to stop it from changing color you have to insulate it from the oxygen. This can be done by fluxing.
  The content of the carbon probably has some effect on the color but it is not a necessity.
 If it is then someone put some bone charcoal in my wood charcoal.
  Soon we may have to have some dinosaur  bone charcoal, If you believe  all the old formulas
you will soon be doing a dance around the crucible and chanting to the stars with a rattle in each hand. In red neck language [that there ain't that hard]
1/4" minus works on the charcoal.

[JCKelly]

Gaddy's work is not exactly ancient.

For whatever reason, it is the calcium phosphate in bone charcoal that gives one the colors

Case colors, at least done with bone charcoal, are NOT the same as the temper colors you get when heating steel from 350F (straw) to 500F (nice blue).

Temper colors are very thin and wear off fairly easily. They are colored because the oxide is so thin it is about the wavelength of light the color you see. Ask me for a better explanation 55 years ago.
Temper colors are the same thing as the pretty colors you see when a bit of oil is on top of water.

[jerrywh]

 Kelly.
  Are you saying that a person will not get colors without bone charcoal in the mix.

[Willbarq]

Just wondering something. Why not use "cowboy" style wood charcoal? Know what i mean? You can buy it.

[JCKelly]

Guys like Turnbull, who color case harden guns for a living use bone charcoal in the mix.
I understand the same is, and was, true of Colt.

Most of what I know about it, save industrial carburizing, is from Gaddy

A couple of decades ago I case-hardened some small parts in an electric furnace, using a small stainless cup to hold charcoal with a bit of Kasenit added. I followed no good procedures, did see a bit of color anyway.

If you are going to all the trouble of case-hardening something for the appearance, makes sense to me to use what the professionals use. Gaddy may not be the last word, but so far as I know he's the last guy to publish a detailed description of the process. Two part article in The Double Gun, winter 1996 and Spring 1997.

[Acer Saccharum]

I've had good colors with just wood charcoal.

[44-henry]

I have researched the bone and charcoal color casehardening process for quite some time and some might find the following interesting. A few years ago I prepared several samples that were exposed to variations of the process. The following photograph shows 1/8" square mild steel samples that were casehardened in a 50/50 wood/bone ratio, 100% bone, and 100% wood. As you can see the samples all came out colored, but the colors are different with the samples treated with wood.



To provide a better understanding of what we are dealing with, these samples were all examined under a scanning electron microscope. The following sample shows the sample treated with the 50/50 mixture of wood and bone.



Observations supported Gaddy's original findings in that the surface layers are highly structured and composed of globules of iron oxide, as the percentage of bone increases these globules become both thicker and larger.

However, when the samples that were treated with straight wood were examined the surface structure basically disappeared as shown in the next photo.



The surface structures are interesting because I feel this largely contributes to the way that the colors appear to the human eye. When I have performed the color case hardening process using just wood (and I have observed a large number of pieces done this way by my students) the colors appear both flat and dull and lack the depth you get with the bone and wood mixtures. I also found that there is a considerable difference in the case thickness/depth on samples treated with the above three mixtures with the wood exhibiting the least penetration. This also supports Gaddy's earlier findings in that the bone acts as a crude energizer, promoting the formation of carbon monoxide gasses in the closed container. So to sum it up, yes you can caseharden with plain wood charcoal, and yes you can get colors, but there are definitely differences in both the case depth and the colors that you will produce.

[bob in the woods]

I find it extremely interesting that the discussion remains centred on wood charcoal and bone, but hasn't brought leather into the mix . I was told sometime ago that the crucible should contain a mix of wood charcoal, bone and leather . My few attempts have used this mix and the results were pretty good considering my lack of experience. Does anyone else include leather ?

[Dan Fruth]

I hope this is not "off topic" but a gunsmith from central Ohio (Ed Meyers) used to make locks, and all his parts were made from 1018 steel. He then carborized the parts that needed to be tempered by placing them in a 6" dia cylinder of steel, and packed them in bone meal. He obtained the bone meal from the local feed supplier. He would put the cylinder in the forge and keep the forge going for the rest of the day, with a turn of the blower every now and then(the time required depended on the depth of carbon he wanted) The parts were then allowed to cool, and he would temper each part as required. His steel cylinder had a lid that screwed on, and a hole was drilled in the top to allow the steam to escape. His locks are still in use today. He passed away earlier this year, but my friend Ken Netting has his original notes on this process. The bone meal idea might work in your case as well.....Dan

[Rolf]

The bone meal idea might work in your case as well.....Dan

That's interesting!! How were the colors on the lock?

Best regards
Rolf

[Acer Saccharum]

Essentially the parts are surrounded in a carbon-rich atmosphere at a temperature where the steel/iron will absorb the carbon.

The different mete rials bone, leather, wood, peach pits, etc, will bring trace elements into the mix.

[Captchee]

       I all I can add to this discussion ,is that for years I have added bone and yes leather  to  my charcoal pack . Then some years ago I had the very great pleasure of seeing first hand  the results of a person who also  has a lifetime of experience and study . His work is impeccable  and of a level  that many of us  will probably never achieve . That person is Jerry Huddleston  also known as Jerrywh.

          Is his way the only way , no . I don’t believe you would hear him say that  or for that mater anyone else .What you will get is a ; this is how  I do it and what works for me .
  . Thus I can tell  you with all honesty , Bone isn’t needed .

 I also know another gentleman who  uses bone and charcoal  but uses an aerator in this quench. Which from first hand experience , I can say  can change  things  to a very great degree .
 
That raises the question of why ?
 Myself I don’t know . Im not trying to down play or belittle anyone’s  information  , but maybe the differences is in what  grade of steel your using ..
Maybe the difference is in the wood  or type and age  of bone  being used combined with  everything else  and  how one packs  it all .
 In the end it all comes down to     ;If it works for you .

 Myself , I still use bone  some may see what im about to say as odd but I don’t use domesticated animal bone . Why , well that’s the way I was taught .  IE you want quality  bone not just any bone
Its also not because the result is better then Jerry’s process . Its habit and by the time I think about it, well   its already done .
 But I would not for one minute be afraid if I left the bone out of  the mix . The colors I see  in what Jerry and  Jim do , are very bold and wonderful .

Anyway , just my 2 cents 

[Acer Saccharum]

Maybe bone is high in carbon? Maybe because bone was plentiful in the 18th and 19th centuries, and wood was scarce, that it became a source of case charcoal?

Regardless, I've used only wood charcoal, and have been happy with the results.

Sifted and graded wood charcoal can be had from Brownell's in 5 gal buckets.

[44-henry]

Just about any source of carbon can be used successfully to carburize low carbon steels, wood charcoal included; however, wood charcoal by itself is inferior to mixtures that contain some form of energizer. In the end you need to ask the question what you are trying to accomplish, if it is colors that you want you can get them with wood only, though they will look different than those produced with a wood bone mixture. If you are interested in case depth and carbon percentage than you are not going to achieve optimum results with plain wood charcoal.

If you have used plain wood charcoal and are happy with the results that is fine, but there are much better mixtures out there for this process.

[T*O*F]

Maybe bone is high in carbon?

If it wasn't, you wouldn't get bone charcoal when you burn it.  We are a hydrocarbon based specie.

Maybe because bone was plentiful in the 18th and 19th centuries

An early form of recycling.  Surely you remember the wagon peddlers pushing their carts around London crying, "Rags, Bones, Bottles today."

[Captchee]

there are alot of maybe's . again it all comes down to what works for you and gives desired results . its pretty hard to dispute what jerry is saying when you look at the quality of his work

[jerrywh]

 Case hardening is simple but then achieving a desired effect is not a simple process. The composition of the pack is only one thing that effects the colors. The warmer the quench temperature is the more blue you will get. That is because the steam bubbles containing oxygen have longer time to oxidize the surface of the part before it drops below about 400°
 Like I said before the composition of the pack has some effect on the color but color can be had with any clean form of charcoal is done correctly. the amount of bubbles and the size of them also effect the pattern. So will anything that adds oxygen to the water such as potassium nitrate. I am not a scientist but have played with this color stuff a long time. 
  This lock was made very blue by simply using warmer water in the quench.
 

[rich pierce]

Of course we all know that bone has minerals in it, but the mineral is deposited on a matrix of collagen fibers.  Collagen is protein, made from amino acids, and has much more nitrogen than wood.  Interestingly, skin, which when tanned becomes leather, also has collagen as its primary structural protein.  So the link between bone and leather in color case hardening may be the collagen protein content, and in return, related to the nitrogen present in every amino acid, but not abundant in cellulose and lignin which are the basis of wood.

[jerrywh]

44 henry.
  Very interesting info on the structure of the metal.  This is very good but all the other factors must be included such as soak time and temperature, temperature of the quench and contents of the quench. These is no way to detect how much the contents of the pack effect the colors if the other factors were manipulated. Although I suspect that all things being equal
your info would stand up pretty well.  It takes a lot of time and money to run these experiments. Most of the color hardening I have done with wood charcoal turned out much better than the samples you showed.