Tuesday, October 13, 2015

Building a charcoal kiln #4

Part 4 of,

"More than you ever wanted to know about building a kiln for making bladesmithing charcoal."

I've got a few more things that I'd like to try.

For starters, my burn chamber is just a horizontal tube of tin. Once the draft gets established, the heat and smoke gets drawn into the coaling chamber nicely. It works OK, and you can't get much more simple than that, but when I look at the diagrams of the traditional earth berm kilns, you can see that the burn chamber is much more enclosed within the body of the kiln. 

The metal drum Iwasaki kilns that I've repeatedly referenced use a separate partial drum to serve as a burn chamber, and that's great. Mine could be improved though. See, the reason that I like the more enclosed fire chamber is that it looks like a smaller fire could be used, since the heat and smoke are more tightly directed into the coaling chamber. By reducing the size of the fire, we are trading a possibly longer coaling time, with the lessening of heat and the force of the flames.......At least that's my thinking.

The second thing that I've been wanting to test out.

The traditional kiln shows the wood being tightly packed and VERTICAL. I did the best that I could, and the back has a higher proportion of vertical, but.....This was a huge PITA, and I doubt that I'll do it this way again. Maybe with a rectangular coaling chamber it wouldn't be so difficult. We'll see what the charcoal looks like.

So here is my quick and dirty improvement to the burn chamber. That's not parallax error, it really is tilted.

The end that abuts the barrel lid has a mating flange that it sort of hangs from and also seals the join a bit, point being that it forms a tighter fit than before. Towards the center of the burn "tube" is the feed door, a 3-sided cut, bent down at about a 45 degree angle. The end of the tube at the left is still fully open. If it bears repeating, I'll take better photos next time. The description is hard to follow.

What I've made here is closer to being a top loading, horizontal draft "rocket stove", and it works so much better it's surprising. The separate air channel on the left let's you pack the fuel port totally full, without starving the fire of air. The burn chamber creates good air turbulence as well, contributing to better combustion. These simple mods make the fire much easier to start, it burns hotter, and it's easier to load the fuel charge (meaning you can cram it full and then just check back every 30 minutes or so to refuel). The slight incline to the chamber might help induce a properly directed draft too. It seemed that way, despite the visible flames occasionally shooting out the fuel port. 

It's still ugly and cheesy looking, but remember, I need to be able to whip this whole assembly out of the way in seconds, when it's time to shut down the coaling process. I can grab a stick and lift this nasty mess out of the way in two heartbeats. Also, don't forget that the galvanized metal that I am using gives off extremely poisonous fumes as the zinc burns off. Don't sit too close, not before making peace with your gods.

And the third thing.......

Right after my last firing, I was sitting around reading about Sumi-yaki (Google : 炭焼き ), looking for more tips and improvements I can make to the process. I found a couple of good ones. 

This is from a site making bamboo charcoal, slightly different, but essentially the same.
Charcoal making process according to the drum charcoal kettle is as follows.
1. pilot flame to burn and raise the temperature of
2. smoke up to 85-95 degrees and make sure that "it was deliberately fart" (strong smell) (0.5 to 1 hour)
3. fired to stop the pilot flame, to limit the supply of air, keep the temperature of the smoke (4 hours)
4. temperature of the smoke if promoted carbide begin to rise (2 hours)
5. temperature of the smoke misses the thermometer When equal to or greater than 180 degrees (one hour) is
6. smoke Open the internal cover Once colorless, do "Nerashi" (about 10 minutes)
7. Exit to close the air inlet and the chimney outlet (total of 8 hours)

When you get to the "Fart-smelling, yellow smoke phase", stop firing and cut back the air supply......huh.

I don't think that I've ever seen that referenced before, stopping the fire (the fart smell....everyone knows that. The yellow smoke has a large sulfer component, I think). The thought behind this is that once you get the yellow smoke going, the wood inside the drum has established a kind of oxygen deprived combustion, so any additional heat input only would be causing potential damage to the coal.
When you get into making traditional bladesmithing charcoal, you quickly realize that there is something missing in our body of knowledge, some little detail. Nearly everyone out there is making nasty, overcooked char. It's fine for the garden, but not as good in the forge. Everything that I've read has you firing the burn, right up until it's time to shut 'er down. Maybe this simple thing is one of the details?

Cutting back on the air supply will further slow the process of coaling, but it also gives greater control. Once you get to the yellow smoke phase, things start to happen ever more quickly. During my last burn, from YS phase to done only took a little over an hour. This time.....closer to 2 hours, but the rate of change towards the end of the process felt much more relaxed. I'm hoping that the charcoal felt the same too, nice and relaxed. We'll see.

So the yellow smoke for me and this Guava I'm coaling went on for quite a while, but essentially, I stopped fueling the fire and cut back the air a bit.

The yellow smoke phase is around 350*F at the stack. 

The partial brick at the front can be bumped either way to give enough air to keep the stack temperature rising.

I didn't really need to do anything though, just sat and watched the smoke.

We are getting close to shut down time. The stack temp reads around 500*F and there is still quite a bit of "white" in the smoke.

The amount of finishing time is one of the more important aspects that determine the qualities of the charcoal. Because I am using this for bladesmithing, I don't want to cook everything out. If I was using this for an indoor hibatchi or a charcoal heater, I would try to cook the charcoal until it was as clear as possible.

I guess that it goes to show just how divorced from the mainstream I am but.....it just occurred to me, the number one use for real charcoal is likely to be for grilling a barbecue, haha. Would you believe that I've not tried that yet?!

Wow! Get a life, kid!

Here is where I shut down, nearly 800*F at the stack.

If you compare the smoke to the prior pic, you can see that most of the "white" is gone. The time interval between the two was approximately 15 minutes.

I dragged the firebox out of the way, piled up bricks and dirt to shut down combustion, capped the stack and called it a night. 

So what do we get this time? Trash or treasure?


I'm thinking trash. Where does all of the wood go?! The barrel was packed as tightly as I could get it. Lots of ash......


Oh well.....it all burns, right?

I grab the shovel and sieve to start cleaning up, but this stuff doesn't shovel. Just past the overcooked stuff are sticks of solid carbon, and they aren't falling apart like the other charcoal that I've made.

Almost the entire burn looked like this......sticks, magically shrunken and transformed. 

It's too bad that the bark is still on the sticks, because that thin outer layer affects the resonant qualities. I've finally made the "hard" charcoal, paradoxically known as "white" charcoal, or electrolytic charcoal. These carbon sticks are now conductive to electricity. The light was pretty flat, but you can see that the charcoal looks silver, not black. Cool, huh?

I don't think that this would be considered true "white" charcoal, but it's getting close. This charcoal kiln is definitely capable of getting up to the 2000*F needed for complete carbonization, and I've been wanting to attempt the making of the "white" charcoal, but to get it right, I would need to open the barrel at the finish, then quickly smother the charcoal. Scary! The burning charcoal gets buried in old wood ashes.....ironically, something that I don't really have much of, haha.

This charcoal is really starting to exhibit the resonant qualities that I find so interesting. The water being completely driven out of the wood, making the carbonized cells ring like bells, each stick like part of a strange looking wind-chime.....I don't know, but it's neat to experience, charcoal that sings.

The resonance is dampened by both the outer bark layer and the amount of wood shrinkage within the stick itself. These didn't ring well.

As you'd expect, a solid bar of carbon rings clean and loud, while one that is covered in tiny plates of carbonized bark – which also resonate, but at different rates/frequencies– sounds flat or muddy.

These sound like tuning forks.

You only get a couple of whacks before some fracture occurs and the stick breaks in two. Some of the smaller stuff must've been fairly dry when they went into the kiln, because they showed no shrinkage splits at all, just solid carbon. When they break, it's with a super high pitched *TINK* that hurts my ears a bit. Some of them shattered forcibly, like a candy cane.

Towards the rear of the kiln, in the area of the vent stack, the wood barely even looks like charcoal. It has a brown hue, but it's not undercooked. There was also an iridescent blue in spots, some strange chemical compound flaring off, I guess.

So, at the very bottom of the barrel I laid four sticks full length, and of the entire load, it was only these sticks that didn't fully carbonize. Everything else was fully cooked, through and through. 

The verdict is in. 

I deem the charcoal kiln a success, though my firing procedure could still use some refinement. This kiln design is far and away the easiest and most reliable way to make high quality blacksmithing charcoal, at least compared to what I've done in the past. I'm having a hard time restraining myself from burning all the time, I just love opening the kiln up, seeing what has been created. Maybe it's because good charcoal is such a rarity? I don't know, but I just love it. 

A big question remains......is this charcoal any good? I am following my interests here, doing this just for fun. I mean....I still need to build a fuigo and small forge, I'm not even prepared to test this stuff properly. Right now, I'm learning the art, getting to know the kiln itself. I'm just seeing what *kinds* of charcoal I can make, and I'm not worried about whether or not the stuff burns hot/cool/too slow/fast, whatever. This batch ended up very "hard".... fun, but not what you want for forging, exactly. 

For forging you want the softer "black" charcoal, not this hard "white" charcoal, at least that's my understanding. When I was using my home made charcoal before, I was using the soft, crummy, and overcooked charcoal for lower temperature work like quenching and tempering, and saved the best hard pine charcoal for welding. It was soooo much nicer to work with, but it was also touchy, too. Get my timing off, forget what I was doing for just a moment and I'd start to hear the metal breath....then hiss, the sound of the steel burning. The charcoal that I made from rotten cedar deck boards could also reach welding heat, but it took MUCH more effort. Not beter/worse, just different. It should be a relatively simple matter to make a variety of slightly differing charcoal that will be task specific. 

Hopefully when Mark Grable reads this, he will be able to comment on what the charcoal was REALLY like, the charcoal that Yataiki preferred for forging his saws. I've got so many questions.......
  • Red pine for forging, so I've heard, but were there different qualities that were used to differentiate? I can imagine opening a bag o' charcoal, sorting through the sticks and making different piles.....Chopping into ever smaller pieces.
  • Is there anything that must be avoided, when choosing? Different species would burn differently, but also might introduce a chemical component that would be good....or bad.
  • What am I obviously missing here? I mean....this is what I've come up with after watching a handful of YouTube videos, written anecdotes and allusions that I've found, and my own slight experience. But mostly this is the product of inference, experiment, and some guessing, haha.
And of course, there is the question of tree species. For all I know, guava might be a terrible bladesmithing charcoal.....I guess that I'll find out. This wood is still fairly wet, but surprisingly, it doesn't seem to matter much. Using dry wood must speed the operation some, but that might not be a completely good thing. This wet wood is shrinking dramatically, and shows many cracks and fissures. That keeps it from being used as part of a totally kickass Halloween themed windchime, true, but it also means that it is easier to split. The hard and solid ones are harder to break.....kind of loud too.

That a person can make a simple little charcoal kiln out of an old paint can, make some char, then start burning steel.....needing only a armfull of bricks and an old bathroom fan (and the paint can).....That's freakin' cool.

I've already got the kiln started on the next batch, this time loaded with all of the sticks lying flat, easy as can be. If anything strange happens, I'll let you know. If you know something that I don't......you let me know, OK?


  1. I'm really hoping guava will be a great forging fuel!
    I'm exciting to see more experimentation in smithing! I might return to it in the future, if I can. I just realized how busy my life is going to be this year, maybe it's good I can't smith for the time being.

    1. I've got too much on my plate right now too! When things settle down a bit, and I can get the forge built, I'm looking forward to making Orishigane.....my own high carbon steel. That should be fun!

      And tiring! All that folding and hammering and folding and....and me with no apprentices, haha.

    2. Is there any flowing water nearby?

      Just make a water-powered power hammer, shouldn't be too difficult!

  2. I can't tell you how exciting this is to me. I hang on every word and can't wait for the next coaling batch. This white char is off-the-charts cool. I'm bringing my little folding BBQ next time I visit.

    1. This is seriously fascinating stuff! I've been so surprised, I bet the next batch turns into solid gold or something. 24kt BABY!!!

      Hahaha Brandon.....you're kidding, surely.....

      But then again.....I really do find this stuff fascinating. I had always thought of charcoal as that filthy crap that you associate with pissed-on campfires but I'm learning that, like anything, there are subtleties. As I unload the kiln, I want to examine each piece, looking at the variety of flare patterns left from intense episodes of explosive pyrolysis. There are all sorts of colors and burst patterns, fans and spatters and waves. There is so much violence happening in that environment that it's a wonder that anything can still manage to come out whole. But it does. Bits of already flaky bark stay attached, small twigs can carbonize as perfectly as 4" thick chunks of solid and wet wood.

      Using the 5g pail method that you've seen me mess with before, I didn't have any consistent success carbonizing larger pieces, only small offcuts. With this kiln, it's all good and really easy, too. The difficult part is loading and unloading. My other batches, you'd get the occasional long stick but it would be brittle, breaking into multiple pieces unless you are careful. This stuff, you toss it in a pile and it still doesn't break. I threw it all in a plastic trash bag, and the bag looked like it was just full of...sticks. They take up too much room! I need to start breaking them down as I unload, but that takes a lot of time too.

      Examining the photos of the last batch, it looks like most of the wood that was packed horizontally along the sides and top turned into.....nothing, just gone, and what did survive was more akin to what I have made in the past. Where did it go?! There was still only a little bit of ash, although it's possible that this Guava burns clean and doesn't produce much ash....that would be nice. I guess that the missing wood just turns to vapor, gets filtered through the other wood on its way to the vent stack.

      This is like anti-woodworking!

      (P.S. Sending you strong psychic mojo to help fight the boat demons/equipment manufacturers!)

  3. Check out Dave J's method, at http://islandblacksmith.ca/2013/03/charcoal-kiln-v-3-0/ There's a great image of how his kiln is built, and a video, either there or elsewhere on the site, of doing a charcoal run. Thanks for sharing your method Jason. May it get better for you!

    1. Hey Aaron!

      Yes, Dave Friesen's website was my introduction to the Iwasaki style charcoal kiln, the design from which this could be said to be adapted. The first installment here....


      even borrowed his diagram (attributed, of course)! As far as improvements go, this kiln has proven to be as simple as I've yet tried, making high quality bladesmithing charcoal with ease, nearly foolproof.

      Of course having said that......I may have burnt up the last batch, not sealing the thing adequately after the last shutdown, haha. I'll check, as soon as the darn rain stops.


Like all of us, I am figuring this out as I go, so when you see something that is incorrect or flat out wrong (and you will!), let me know. This is a learning process. Real people and names, please. Constructive comments and questions are very welcome, but hate speak/politics are not! Life (get one!) is too short.

Thanks, Jason