Please describe the physical properties of torrefied spruce

[Bryan Bear]

I haven't seen quite as much discussion of torrefied spruce here as I have elsewhere but I figured it would be a good topic for this forum. I am pasting this from what I just posted on another forum where it has been discussed a fair ammount:

Describing working properties and physical characteristics of timber can be almost as problematic as describing tone. With that in mind, I thought it might be interesting to try to get a bunch of descriptions of torrefied spruce all in one place. Torrefication is all the rage and it is my impression that many of us don’t really have a handle on what the wood feels like or how it works (let alone any tonal implications). I’d like to see some of the people in the know describe what torrefied tops are like and how they work and perhaps try to relate that to what one would expect from a newer non-treated top. If possible, try to keep this from becoming a debate about whether or not it is a good idea or what effect it may or may not have on a finished instrument. Even more so, let’s resist the urge debate the difficulty with getting useful data from comparing finished guitars.
I am a hobbyist and as such, have not handled any old spruce tops or torrefied spruce. Further, I still have a lot to learn about wood characteristics and identification in general. I, for one, don’t have a well-developed vocabulary when it comes to describing various woods. I have casually followed the discussions about these tops but not spent much energy on them because I didn’t see myself ordering any in the near future (I build slowly and have plenty of regular tops waiting for me). Then I go to thinking about some spruce I have in my stash that has always seemed off to me. I cut up an old exterior spruce door for brace-wood. I even made an ukulele top from it. I could tell it was spruce but with my limited experience, I could not tell what kind. It seemed like Sitka but different somehow. It was darker, and not quite brittle or crumbly but certainly carved differently than I expected. When I made the uke top, I even questioned that it was spruce at all because I discovered that it was not translucent like the other spruce I have.
This door had been fending off the elements for 35-40 seasons and here in St. Louis, it would have seen very hot and very humid summertime conditions and cold dry winters with wet springs. Our climate is also famous for drastically and frequently changing conditions. I have fond memories of snowball fights in shorts and t-shirts from my youth. Certainly this wood is well seasoned. Could it be that I do have a sample similar to torrefied wood or am I just way out of my element here? One other curious note about this wood, this is the only bridge I have had come off (HHG) and with its nylon strings it has seen much less tension than my other instruments. Are there gluing protocols for dealing with old/torrefied wood?

[Stephen Neal Saqui]

So far I haven't seen anything about the changes in cell structure in soundboards of "Torreficated" wood. Only judging from the proponents words it sounds like just one more gimmick.

I remember a truly scientific study years ago that looked at the cell structure of tone woods of the great violin makers. They showed that the cell structure in those woods had been altered by soaking the logs in rivers for long periods to "cure" the woods. It was one of the best of the studies done that showed significant change in wood structure in fine instruments compared with instruments who's wood had not undergone the soaking.

I had a similar experience than you, Bryan, when I found a piece of driftwood spruce on Stinson Beach near San Francisco in 1972. I finally resawed it and got enough for two ukuleles and one small guitar. I built a tenor uke for a guy in SF...it's the best sounding uke I've ever made. I can't be making claims about its curing though I'd sure like to! Can't wait till I make the small guitar with it as well.

My first question about "Torrefication" would be about the change in cell structure when you bake wood in an oven. My gut only tells me that they've shortened the the lifespan of tone woods for a little bit of temporary sound improvement.

I hope we do get some solid information...in time we will, if it doesn't just fall flat.

[Stephen Neal Saqui]

The absence of input here possibly shows just how horrified folks are about torrefied wood!

[Bryan Bear]

It really is interesting. Torified spruce is talked about quite a bit on other fora but nothing here. . .

[Stephen Neal Saqui]

You got me. But here's a study of torrefied wood and cell degradation. Which is maybe a great thing for wood stove pellets...

http://www.sciencedirect.com/science/ar ... 3411005071

[David King]

I think we need some definitions here. Does torefication imply a certain temperature and duration?

[Bryan Bear]

To my (limited) understanding, torrification as it relates to soundboards is different from baking. Wood is heated in an oxygen free environment. I believe it is heated beyond its normal flash point. How this is done is a bit of a mystery to me, I have heard that it is like a large autoclave but I don't know if that was only speculation. Apparently Yamaha has been doing it for a long time. Martin has begun to offer it on some models and has made claims that they can dial the resultant wood properties in to match guitars made from various eras. I'm sure that is mostly marketing hokum. . .

I Google search for torrefied spruce returns quite a lot of hits and some of the info seems pretty suspect or at least based in speculations and assumptions.

The people that I have heard talking (actually read) about the wood they have handled seem to agree that it feels noticeably different. I was just trying to get a single place where people could post their descriptions and discuss them. Hopefully to identify common themes and solidify the vernacular when discussing the various descriptors.

[Stephen Neal Saqui]

There sure are a lot of folks making them. I'm highly suspect of the whole thing...it's so far away from natural aging and the cell structure no longer resembles the original wood...I repeat, I'd be worried about longevity. I understand the fast buck phenomenon with all the makers putting out "old Martins" for rich guys. But I don't see much future in it and I'd rather spend my remaining years building fine instruments that will last.

Still, I'd like to know more about it.

[Bryan Bear]

Still, I'd like to know more about it.

Me too. I'd prefer to hear from people I know from these type of fora too. I tend to be skeptical of any info coming from a commercial venture. . .

[David King]

I thought everyone was making laminated tops with honeycomb layers. Has that gone out of fashion?
If you heat wood above the flash point in an oxygen-free environment don't you end up with charcoal?

[Bill Raymond]

If you heat wood above the flash point in an oxygen-free environment don't you end up with charcoal?

That's my understanding, David, however, it's possible that there's some intermediate stage where much of the gaseous elements are removed, but the remaining wood has not been completely (nor even partially?) converted to charcoal.

[Larry Davis]

"Oxygen free" environment implies use of vacuum kilns which have been in commercial use for decades. Heat source is provided thru electric heat blankets between layers of wood. The darkened color of over heated wood is in fact insipient stage of charring.

Marketing of baked tops will peak when sellers promote the first "master" grade torrified spruce set.

[Michael Lewis]

Larry, that sounds like it might cause the wood to become more brittle. It seems we (humans) want to make young things older (relic and distress) and older things younger (refinish). Just an aspect of the Human Condition I guess. The grass is greener somewhere else conumdrum.

[Mario Proulx]

The flash point of spruce is 350-360°C(662-680°F) and the spontaneous combustion temperature of spruce is 390-400°C(734-752°F), so to have the slight charring we see, and the requirement of an anabolic chamber suggests that torrefied(sp??) spruce is baked at or near 750°F.

When I make charcoal, the gas escaping the container through several holes roars and burns like a torch. A BIG torch! What happens when we make charcoal is that we burn-off all the volatile components. I suspect that this is what the torrefication(sp?) process seeks to do, though stopping short of causing the complete breakdown of the wood structure(as we do with charcoal).

That's my best guess....

[Bryan Bear]

Mario points out a distinction that I may have misunderstood. I said "flash point" but I may have meant "combustion point." I don't really know much about the process. Even Stew Mac is now selling for refined tops. Who knows how long the fad will last or if it will catch on. . .

[Larry Davis]

Yep, increased brittleness and decreased strength are torrefaction results to some degree or another regardless of baking temps and baking time. This is a good article on early USDA torrefaction study and possible commercial value. Spruce tonewood is certainly not baked to the high degree of charring cited in this report. Click the pdf download (on the linked site) for the full report which includes the use of torrefied biomass in making charcoal as Mario describes. A search on torrefied lumber reveals some fastner and gluing problems with this process also. I suppose it remains to be seen if bonding issues arise with baked tops eventually.
http://www.srs.fs.usda.gov/pubs/36341

[Michael Lewis]

Thanks Larry. Mario, what is your set up and process for making charcoal? I'm interested in making biochar for putting in my garden.

[Mario Proulx]

What is biochar and what does it do to a garden?

Making charcoal is easy. I've used both one gallon and 5 gallon paint cans. If it has a plastic lining, toss it in a fire to burn it off. Punch or drill a half dozen or more 1/8" holes in the lid. Fill it with wood chunks, fix the lid tightly, and toss it in a fire, or place it on a propane burner(turkey fryer or similar), and that's it. I make campfires often(we burn all of our combustible garbage and of course, my shop scraps), so that's where I make my charcoal. The escaping gas will burn with a loud roar and shoot a flame almost a foot long, so it's not something to do with little tykes nearby. I keep wanting to try larger holes to try to find the happy place where the sound and flame will be more subtle, but i kind of enjoy the show.. <bg> The charcoal is ready when there no longer is any flammable gas escaping.

[Larry Davis]

Mario, ton of biochar info on Google for all levels of study including commercial sources. Interesting reading and bet with your skills building a char stove would be a cake walk http://www.biochar-international.org/technology

[Bill Raymond]

Michael, as I understand it biochar requires charcoal, nutrients and beneficial microorganisms that live off the nutrients adsorbed by the charcoal. I've bought biochar, but it's expensive. I have considered trying to make it with barbecue charcoal, crushed, with the addition of fertilizer and some compost, leaving it to "stew" for a bit, then mixing into the soil--the fruit trees in our small home orchard need all the help they can get growing in this heavy north California clay after fighting off the ground squirrels and feral pigs.