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Thread: Torrefied, thermally cured, "roasted wood" for the home shop

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    Registered User j. condino's Avatar
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    Default Torrefied, thermally cured, "roasted wood" for the home shop

    Some very good friends of mine have been getting excellent results in their instrument builds using some variation of the torrefaction process whereby they basically cook the wood for specific times and temperatures.

    In the wood products and flooring industries, this is pretty common and makes for very hard and durable floors. In the instrument world, I've seen an huge variety in the spectrum- from barely cooked light colored woods to pretty much crumbling burn toast on the inside and out that I would never consider using. I've also seen some very nice applications to moderate hard woods as ebony substitutes.

    There is a ton of information and snakeoil floating around the world wide waste of time, so as is often the case, I've been running my own tests here at Condino World Headquarters.

    Back when I lived in the high desert, I'd store all of my woods out in the barn rafters that got around 175 degrees in the summer. Pitch would leak out of them like stalagtites....and there was a noticeable difference in the woods after a few years.

    A good friend of mine has a dedicated giant oven in the wood shop, sitting right next to the bandsaw. It has dedicated lines of nitrogen gas plumbed into it. Another friend has a giant industrial process. I've been searching for a big chemistry lab autoclave type setup. On the telecaster forum, I saw a lot of decent results with very low tech applications. Like always, I made several dozen test runs. In the end, this version worked quite well:

    NOTE: All of this is meant to be a review of my experience, not an invitation to burn your house down!

    -Step #1 - the most important part of the process!!!!! Pick a weekend when Mrs. C is out of town!

    - pre heat the house oven to 170 degrees F.

    - wrap all of the wood in several layers of aluminum foil to remove the oxygen (combustion!). True, it is not perfect, but this eliminates most of it. You may get a slight toasting on the outside, but like at breakfast time, it scrapes right off.

    -insert wrapped wood into oven leaving plenty of room for air to circulate.

    -turn over temp up to 375 degrees F and let cook for 2 1/2 hours. Turn oven down to 160 degrees F for one hour and then let everything cool completely.

    VERY IMPORTANT: Cook a dinner of fish or spicy Indian food or something to cover up the funny smells in the house before Mrs C. returns! Actually, the smell was quite pleasant...like making cookies or the smell inside of a maple syrup cook house back when I was a kid in the Adirondacks.

    This resulted in a modest sort of thermally curing, but no carmelized colors like true torrifaction.

    Next day: repeat process.

    The second cooking resulted in pretty even carmelizing through the entire spruce boards; much less with the maple boards. Wedges were cured out slightly more; solid 1" boards were much lighter. Note one of the boards.

    Secured in my ancient old Emmert pattenrmaker's vise:
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    Last edited by j. condino; Aug-25-2022 at 6:46pm.
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    Registered User j. condino's Avatar
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    Here are the wedged boards and the 1" thick. You can see the "toasting" on the outside of the thicker boards (closer to the over heat source?), that planed off very quick. The thicker was much lighter; I could probably have run it another session or longer, but I didn't want to go too far. I rather like the light version, as it reminds me of some of the century old spruce I have worked with.
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    Last edited by j. condino; Aug-25-2022 at 6:47pm.
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    Registered User j. condino's Avatar
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    They glued up well with hot hide glue, but were extremely thirsty. I "seized" the wood first, let it cool, and then added a second application of hot hide glue about ten minutes later. You can see a slight racing stripe area, just like with regular air dried wood in the sapwood region. Overall the wood is VERY rowdy and responsive, tends to chip out a little, and is VERY loud. It reminds me of the best pieces of western red cedar I have worked with, or maybe the real Lucky Strike redwood tree. It is also very similar to the recovered 100+ year old Alaska bridge billets that Bret from Alaska Specialty Woods was selling a few years back. I made a couple of double basses from those and it was spectacular. How do I get a commercial pizza oven big enough for 4' long bass tops in my small 450 sq. ft shop????? (I'm sure I'd make WAAAAAAYYYYYYYYYYYYYYYY more money selling piizza than mandolins....)

    'Planes great, smells nice, interesting stuff, and great to be able to not be dependent on another outside source. I ran a bunch of maple too. I'll show it in a month or so when I'm ready for the backs. I could have cut the racing stripe out, but I'm going to make this a blackface as part of an entire quartet, so it is fine.

    Let the " whole lotta nuthin' " rage begin.....
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    Last edited by j. condino; Aug-25-2022 at 7:31pm.
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    Registered User j. condino's Avatar
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    BTW, the boards I started with are North Carolina red spruce, cut about 30 miles from here up near Bryson City. I sourced them from The Hampton Brothers- the coolest young guys in the tonewood business. They also have a commercial torrefaction process that they will do for you and they sell ready to go T'd wood, but it is more fun to be stubborn and keep up the dirtbag luthier life!
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    Did you weigh the boards before and after to see how much lighter they were?

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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    Thanks for sharing!

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    Registered User j. condino's Avatar
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    Quote Originally Posted by CarlM View Post
    Did you weigh the boards before and after to see how much lighter they were?
    Nope.

    Weight had nothing to do with my goals.

    I would suspect that a lot of the moisture forced out by heat would settle back in when the boards equilibrate, in a similar way that plenty of folks over / under use a woodstove & a dampit.
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    Registered User Simon DS's Avatar
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    Interesting, thanks.
    I imagine that some of the volatiles from the sap would be replaced by water vapour.
    I wonder if there are chemicals that are more stable than either water vapour or raw sap.
    Maybe something waterproof...
    Aaah, the chemistry of mandolins!

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    Adrian Minarovic
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    That is almost exactly what I did few yars ago. I posted about it here:
    https://www.mandolincafe.com/forum/t...=1#post1645390
    I've read several woodworking scientific papers and pre-dried the wood to 0% MC as they recommended before I packed it to the aluminum foil. (in oven set to 110C for an hour)
    I weighed the billets and they lost few grams (spruce wedges) after they reached equilibrium again in few days after baking.

    I made two identical mandolins (all wood from same billets and same specs) just one top I roasted and honestly couldn't hear a difference in tone. But the wood had slightly "dryer feel".
    One reads that torrefied wood is not as suspectible to humidity and indeed it barely reacts to steaming out dents so you have to be more careful not to ding your mandolin before finishing.

    In violin world Don Noon is one of the award winning makers who torrefies his own wood but he uses wet process with steam pressure chamber. He is retired rocket scientist and he tuned up his process to maximize parameters prized by vilin folks - loss of weigth and damping and increase in speed of sound. He posted some notes on maestronet forums.
    Adrian

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    Registered User Sue Rieter's Avatar
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    Quote Originally Posted by Simon DS View Post
    Interesting, thanks.
    I imagine that some of the volatiles from the sap would be replaced by water vapour.
    I wonder if there are chemicals that are more stable than either water vapour or raw sap.
    Maybe something waterproof...
    Aaah, the chemistry of mandolins!
    I remember as a kid in maybe 6th grade, doing a science experiment called "distillation of wood". We had the wood pieces in a test tube and collected the vapor that came off as we heated it. The vapor passed through a jacketed tube to cool it, and we took off different fractions of liquid, which we later tested to see if they were flammable or not (some, of course, were). Pretty memorable, ha ha, that was over 50 years ago!

    James's kitchen oven wood experiment reminded me of that, though as I recall, we heated until there wasn't much left of the wood.
    "To be obsessed with the destination is to remove the focus from where you are." Philip Toshio Sudo, Zen Guitar

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    Registered User Tavy's Avatar
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    Just thinking out loud here (as a former Chemist), would placing under vacuum be equally effective at removing the volatiles which are supposedly driven off by torrefaction? I ask because wrapping in several layers of foil may well stop the wood from going up in flames - always a good thing IMO - well done there James - but may tend to "bake-in" the volatiles as tars rather than driving them out?

    Of course, I'm not sure it's been established what the proper mechanism of action of torrefaction is so whose to say which is better. But conceptually, a vacuum bag - of the kind used for veneering - and a small pump would be much easier and cheaper to run.

    On the other hand, if the desire is "accelerated ageing" then the application of heat will certainly speed up the reactions that would slowly take place over time and is maybe the closest we're going to get to stacking up the wood for a 100 years.

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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    Cool thread, James. I've been messing with torrefaction after a couple of brief conversations with Don MacRostie.

    As luck would have it, a friend has been remodeling his kitchen and had a surplus high-end GE double wall oven with convection. I put wheels under it and fitted it with a cord, so it can go outside when it's time to "cook" (as Walter White says). That way it doesn't interfere with one's quality of life, and you don't have to smoke too many cigars to mask the stink.

    Don turned me onto the Thermowood Handbook as a resource. The Scandinavians are using torrefaction for treating building materials like deck lumber against water incursion and bug infestation. The Finns are pretty much the keepers of the tablets. There's a lot of interesting science in the handbook, but if you want to cut to the chase, Page 7 will tell you just about everything you need to know.

    My intention is to seal up the top oven unit so it will hold vacuum. That's comparatively free, as opposed to bleeding nitrogen into the oven. If you can't prevent oxidation, you're just making charcoal.

    Just curious: How big of a billet do you need to torrefy in order to carve a bass out of it?

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    Adrian Minarovic
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    Quote Originally Posted by Jonathan Ward View Post
    Don turned me onto the Thermowood Handbook as a resource. The Scandinavians are using torrefaction for treating building materials like deck lumber against water incursion and bug infestation. The Finns are pretty much the keepers of the tablets. There's a lot of interesting science in the handbook, but if you want to cut to the chase, Page 7 will tell you just about everything you need to know.
    I've read that book and you must be aware that they are turning basically green wood into torrefied and their kiln and process reflects that. Their kiln is not simple oven but has built-in humidity control so the ambient RH will not cause severe checking of the wood while drying to 0%. Then they will rehumidify the wood while it is still cooling.
    We usually take wood that is already at 6-8% MC so we can fairly safely dry it down to 0 if we heat it slightly above boiling point (I have weighed my wood during this to make sure is is at 0). The process of main baking is simple heating and keeping it at the temp for several hours and then glradual cooling. I left the last phase to nature by keeping the billets in my workshop with plenty of natural airflow.
    I have no idea how much of the resins/saps remaining in the dry wood liquefied or evaporated but certainly there were leaks on the surface of the wood and dry residues trapped/condensed on the foil
    The wet process produces quite murky juice so it probably extracts more from wood but is much more dangerous with steam at high pressure/temperature and requires special autoclave.
    Adrian

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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    Quote Originally Posted by Jonathan Ward View Post
    My intention is to seal up the top oven unit so it will hold vacuum. That's comparatively free, as opposed to bleeding nitrogen into the oven. If you can't prevent oxidation, you're just making charcoal.
    I’ve made a few vacuum ovens, including a few for the Air Force, who use these things for degassing epoxies and other sealants that otherwise might have problems in altitude service - not uncommon application. Mostly, though I make high vacuum apparatus. To reinforce something the size of a kitchen oven against even a partial vacuum requires a very strong chamber. Do the arithmetic: 15psi/square inch. For about this size, as a cube, say, half-inch thick stainless with at least one stiffening rib per side, including the door, all welded, is minimal. If made for only ‘rough vacuum’ which is what you’d want, a mechanical (oil bath) pump of a few cfm is appropriate. On the heating side, the oven’s original heating elements, equipped with high vacuum feedthroughs, would be fine, but remember that, without much convection, the parts you put in will mostly be heated by infrared, and not uniformly. Other than that detail, there’s some science where vapor pressure of specific compounds at temperature comes into play, as it is the way substances are removed from the wood; that is, they liquify, diffuse thermally to the outer surface and evaporate. Just measuring weight change doesn’t tell you what you removed; that’s where you look to what’s published.

    So, after this long (actually way abbreviated) note, if one had a vacuum bag that could take the temperature, you’d be tens of thousands of bucks ahead.
    Or, go with nitrogen. The amount you’d use, if that oven was decently sealed, is ‘not much’ but you do have to consider whether the volatiles are being carried out by the gas flow, or just condensing elsewhere. Any stuff that just goes to the oven walls, or a bag, can simply re-deposit on the wood. Hot-to-cold is how it works, either in vacuum or atmospheric pressure.

    Personally, other than appearance, tradition and hand tools, I’d think just using something other than wood is the way to get different material properties.

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    Registered User j. condino's Avatar
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    Don is a friend of mine; I've seen his setup in action in the world's coolest old chicken coop...

    I've read the thermowood handbook and a ton of other data that is available on the process. Nobody seems to be hiding the information. The challenge is sorting through all of it and bringing things back down to a place where I can use it in my own workshop. I do have a giant vacuum press setup that I use for bass work, but I don't know where I could buy readily available bags that can handle 375F as well as likely burning out the vacuum pump's innards.

    I have plenty of commercially torrefied boards for comparison and my results are very similar to those with virtually no investment. I'm still learning (a lot), but I can say with confidence that on the maple and neck side of things, torrefied maple necks on the electric instruments are incredibly stable and using the process to create ebony substitutes is likely inevitable.

    Jonathan: Bass billets tend to be approx 48" x 17" and almost 3" thick at the widest point of the wedges for each half. I'm building two giant 7/8+ size right now that have a lower bout that is 30" wide!
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    Registered User Steve Sorensen's Avatar
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    Default Re: Torrefied, thermally cured, "roasted wood" for the home shop

    My process of considering why we would want heat-aged wood goes back to the desired result -- wood which behaves more like the aged material in excellent sounding old instruments. So, I started thinking about how instruments were carted about by musicians over the years. No air conditioning in the cars, hot dance halls; then cold dry winters, in and out of the case.

    As I tore out a wall of my house to add a bay window, I was impressed by the dry, hard, tuneful ping of the 50-year old studs which had been facing similar, but more extreme conditions inside and un-isulated wall. That aging process of the fir studs, inside the wall of a 40-year old Southern Californian house, produced wood which smelled, cut, and tapped like the 1920s instruments I had found so tuneful.

    However, instead of going for a one-day aging process, I started what I called "Wedgewood baking" -- I realized that the pilot light in our antique Wedgewood stove kept the inside of the oven at about 120 degrees. So I put a billeted stack of maple backs (then Sitka spruce tops) in the oven and left them for several months.

    Of course, during that time, we needed the oven ... so the wood would come out, sit in the real world and cool for several hours, then go back into the old Wedgwood.

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    The results gave me wood which reminded me of the old studs that I had cut from the wall, of old boards up in the attic of our Wyoming barn when I was a kid, and the old instruments that I had played and smelled warming in my hands over the years. There is a difference from the commercially Torrified wood that I have purchased in that there has not been the carmelization and extreme drying of the commercial vacuum oven.

    So, these days, almost all the spruce and maple I use for mandolins goes through the Wedgwood Baking routine. I feel it does give a bit of a running head start on the maturation process suffered by those fine old instruments as the traveled around the globe over the decades.

    Steve
    Steve Sorensen
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