Wood Torrefying & Torrefaction DIY

Anyone not familiar with this term should look into it, as it’s pretty darn neat. It is essentially baking the wood in a low oxygen atmosphere to make it more stable. It has been popular the last few years in the guitar-building community. There are a few places offering it for sale, but there seems to be a severe lack of information on a DIY or poor man’s way of simulating the process at home. Apparently, the Vikings used this process centuries ago on the wood for their ships, but again I came up short on any information on how they achieved it without modern technology. Several threads online talk about people baking their wood in a conventional home oven, but there is still oxygen present. Does anyone have any insight or ideas on how to do this at home?

Torrefied Wood there is also thermally modified lumber. I don't think either process is a DIY project.

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Originally Posted by Dean Coss

It is essentially baking the wood in a low oxygen atmosphere to make it more stable.

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A friend of mine, Paul Menchhofer, fires pottery in a low-oxygen atmosphere - he makes the largest Raku fired pottery in the world. Unlike normal pottery firing where the piece is taken from the kiln after slowing cooling, a Raku piece is quickly removed while glowing hot and placed in a chamber with some combustible material (like newspaper or wood shavings) then the chamber is sealed. The combustibles burn and remove all the oxygen from the chamber. This method is nearly always used on small pieces due to the difficulty of handing large yellow-hot objects quickly. The chamber is typically a steel drum or a pit dug in the ground.

For the large pottery vessels, Paul built a large kiln with tracks to move a cart with the fired pieces out of the kiln. He then lowers a large stainless open-bottomed steel "can" over pottery, cart and all. A ring of cay was positioned on the concrete floor ahead of time to seal the can. Strips of newspaper hanging in the can burn to remove the oxygen.

If interested in the Raku firing, I shot a short video of the process. We had to wear protective suits. (Paul edited it the video and added the pictures and music)
FIRING: http://www.paulmenchhofer.com/video.html
Raku can give brilliant iridescent and metallic colors and unique textures.
SOME POTS: http://www.paulmenchhofer.com/gallery.html
IN THE STUDIO: http://www.paulmenchhofer.com/workshop.html

Perhaps the Vikings you read about used a method similar to raku to remove the oxygen in the oven.

Perhaps you could adapt something like the Raku method to cook wood at home. It seems like a sealed chamber for small pieces might not be hard to make but one large enough to hold lumber would likely be very expensive. The initial oxygen could be removed by flash combustion, as with the pottery, or perhaps by displacement with CO2 or nitrogen gas. Seems like that would also be expensive for a large chamber. I suspect oxygen that came out of the wood might need to be removed continuously, perhaps by introducing additional combustibles. All this is speculation since I know nothing about the requirements of the "torre..." process.

JKJ

Interesting info on the raku pottery and great video. I took a pottery class years ago at the local community college and loved it. However, I didnt take the advanced class that got into raku pottery. Looks like a pretty nice setup that your friend had in the video. I’ll have to do some more digging and find some other ways that torrefied wood is made, as wood doesn’t get up to temperatures like the ceramics do.

I suspect if you did use combustion to remove the oxygen you would do something like bring up the oven to temp then electrically light some combustable. I'd probably first try introducing and igniting combustable gas such as a hydrocarbon, monitored with an oxygen sensor. Since this produces water vapor that would need to be monitored.

But simply displacing the oxygen instead with CO2 or nitrogen seems a lot simpler. (Nitrogen is handy to have around anyway - I keep it in the shop for oxygen displacement and other uses.)

If you are inclined to research and experiment I'd be glad to loan or give you a spare lab oven, currently stored in the barn. It runs on 220v, good thermostat, all stainless steel. I forget the internal size but it may be 24" wide or so. You could modify the oven as desired and keep it forever, I think I'm done with it. (A woodturner/chemist gave it to me years ago.) If you are interested and get up towards Knoxville, stop in, or I could send it to Greenville the next time my son visits with a vehicle larger than his motorcycle!

JKJ

Dean, I'm not saying this is a good idea. I read an article in a British working magazine about it, and wanted to try it at home. But did not want to use the oven. I wrapped a couple of pieces of a maple tree branch in multiple tight layers of aluminum foil. Then placed them on my outdoor gas grill, around 400F for four hours. When "done" they were nice and brown and intact, except for one corner of one piece which was a bit charred. I wasn't too impressed with working with the wood, and didnt end up with any usable objects from turning, and the pieces were too small for any flatwork. But in theory, maybe that's one poor man's way of doing it.

Greetings, Please be aware that heating CO2 in a cylinder can be disastrous! CO2 cylinders are filled to only 68% of their water weight capacity so that when they warm to room temperature the expanding gas reaches a pressure of about 875 psi. If heated, that same cylinder can reach 3000 psi at only 150 degrees F.

This is NOT something you want to play with!

You are better off pulling a vacuum and heating wood that way. There are herbal drying ovens that do just that. Not cheap but much safer!

I had pretty good results by wrapping small pieces of wood in aluminum foil and heating in a toaster oven, as mentioned above. I've thought about building an oven large enough to do a real load of wood, enough for a cabinet or piece of furniture anyway. My thoughts have revolved around building an insulated sheet metal box. The door would be sealed against a silicone gasket. Heat would be electric. I would flood the chamber with CO2 after loading/sealing, and leave it with a small flow going in to make sure no O2 gets in during a run.

The easiest design to me would be a lot like JJ described, a tall cylinder that seals at the bottom. The wood would be stood up vertically inside.

John

I have no knowledge about the process, but a friend that works at a cabinet shop gave me some scraps of what he called roasted curly maple. It was strikingly beautiful when finished and a pleasure to work. A quick search showed some sources - here is one - http://sharpslumber.com/caramelized-...t-curly-maple/

I wouldn’t use enough of it to try a DIY, but for those that would it can provide a really nice material to work.

I have used some commercially "roasted" poplar. It was pretty and I was intrigued enough to wonder about what other roasted woods would be like to work with. I did find the poplar a little brittle, but I was using it in an application where I was bending thin (~0.090") pieces with gradual bends. The color was a bit like walnut. I thought it worked fairly well as a tone wood in musical instruments.

I was given a piece by one of my wood suppliers who didn't stock it but had a piece left over from a special order and thought I might be interested. When I ran out of it I didn't seek out a source.

I'd love to try some roasted curly maple, but not enough to bother with a diy project at this time. It does sound like an interesting project though.