Baking vs Torrefaction
 

Recently I’ve been thinking about what makes the Atkin guitars that I’ve purchased so incredibly warm and rich. As a player and not a builder, I’m still very interested in what makes guitars tick, and realize there’s no magic bullet for creating a desirable tone. There are so many variable at play inside the building process, including the ear and opinion of the player. Everyone wants something slightly different.

After owning, selling and trading over 40 guitars over the past 10 years, I’ve currently settled (yes this will change again, I know this) on a tone that I prefer. Atkin seems to have nailed it, and has done so with a method that seems to transcend both body style and tonewood. Rich, full, resonant and even. All seven Atkins that I’ve owned display this characteristic (I currently own three).

I dug deep in their video archive and figured out that they bake - and don’t torrefy (spelling?) their tops. See the 9-year-old video here



Maybe that’s something?

Then this weekend I listened to the luthier on luthier podcast with luthier James Condino where he mentioned that he prefers baking his tops in a similar fashion rather than using torrefied woods. The process releases moisture and resin but doesn’t chemically alter the wood like what is done in the torrefaction process.

You can listen to podcast 83 with James here:

https://luthieronluthier.libsyn.com/

This seems to me to have validity as a potential sweet spot for enhancing but not altering tops’ resonance.

Is anyone aware of other builders that utilize baked tops? Anyone here a builder that has real hands on experience with the difference between the two?

*Gets out the measuring tape to see if guitar fits into the oven....:D

could be.....

you may see "baked" referred to as "roasted" also - I think that's also a common moniker for it. I see a lot of roasted necks and fingerboards which purports to add stability and make the wood harder and stronger.

The difference is that torrefaction heats the wood in a vacuum so there is no oxygen and the thermal change happens without "burning". Baking/Roasting happens with oxygen so the wood actually does cook.

Kiln drying has been around forever - its a tried and true method of stabilizing and strengthening wood.

I imagine doing that to a top lets you make a stronger top wood so you can make it thinner, maybe, so it is more responsive and without worrying about breaking.

I also think by nature of the process, torrefying happens at a much higher temperature. Baking has to stay below the ignition point. So the former would seem to have a bigger impact on the chemistry of the resultant wood.

Interesting idea and I think, as you opened with: there are so many variables. I think one builder will find their sweet spot with one type of wood and another will find there's in another spot.

Interesting to chat about .

Torrefied tops smell of coffee, baked ones of pastry and then there may be ones that would smell of bourbon if only you could make them out of white oak? :D

Almost: https://en.wikipedia.org/wiki/Torrefaction#Process

Putting wood that isn't 100% dry in a vacuum could well destroy it; have you ever seen what a cup of water does when you put it in a vacuumchamber and activate the thing?

What I always wonder is to what extent ageing through torrefaction or equivalent also locks in the age, IOW, can you still expect the wood to continue to evolve under your playing? I've been listening to a couple of comparison videos of the Eastman E1OM with and without aged top, and I tend to prefer the non-aged one. OTOH, there's a video (out of a far-Eastern store) that compares a new E1OM with one that has been played a few years and there the "old" one has a clear advantage to my ears.

I have a 1980 RQ Jones walnut square neck resonator. He somehow microwaved the wood prior to construction. It sure sounds great.

https://scontent-ord5-1.xx.fbcdn.net...Xw&oe=662CCEB1

https://scontent-ord5-2.xx.fbcdn.net...5w&oe=662CD18E

So my understanding is that the process goes like this:

draw a vacuum under temperature, removing moisture from the wood
backfill with nitrogen and bake
pressuring with high humidity to re-inject moisture back into the wood

I had always understood that Atkin torrifed the spruce on their guitars. Here is an article from 2015 that refers to the process as torrefaction, including this quote from Alistair Atkin:

My understanding is that torrefaction of wood for guitars has evolved over the last decade or so. When the process first became popular, the wood was often torrefied in a manner similar to other industries, but builders found the wood to be too brittle. Over time, builders figured out that the wood needed to be dried at lower temperatures and/or for shorter periods. I attended a “luthiers’ coffee chat” at the Fretboard Summit a couple of summers ago in which Dana Bourgeios discussed the evolution of torrefaction of the woods they use (including the fact that they no longer torrefy wood in-house).

Baking vs Torrefaction
 

Not sure. Check out this recent video at the 12 second mark

https://youtu.be/44FbNVCzQgw

Nine years ago, the process he described in his video may have been loosely tied to the term torrefaction, but now there’s a distinction between the chemically altering process and baking the wood.

Maybe?

Keep watching that cup.

"One key advantage to vacuum drying is reduced drying time. The drying time in a vacuum kiln is significantly less than in a conventional steam kiln. For example, a recent study found that a 1-in.-thick hard maple charge was dried in a vacuum kiln in 2 days (58 hours), whereas a paired 1-in.-thick hard maple charge was dried in a conventional steam kiln in 12 days (288 hours) (Lyon and others 2021). This advantage is even more pronounced with thick stock, such as large table slabs or mantle pieces."

https://www.fpl.fs.usda.gov/documnts...fpl_gtr287.pdf

Time to update your understanding. If you want to create fuel then high temperature torrefaction is your thing. If you want to make instrument wood a lower temperature would be better. The process is slower but it can be done at a temperature below the ignition point of wood. The catch, good temperature control and uniformity throughout the oven. The bulk of the wood done for guitars are done this way (just saying most as I do not know if Yamaha is still doing their tops themselves). I can not find the graph I saw years ago on the elements that decompose compared to temperature. Found this though.

https://www.mdpi.com/bioengineering/...00016-g001.png

Most of the charts have torrefaction starting at 200 C, nice of Nature to round off to a nice even number. But when you are doing biomass you do not want to go 30 mph when you can go 60. Oh, I just remembered, Taylor does their own. Wood going into a standard industrial oven, wood implode if a vacuum was pulled. They could just purge with nitrogen but there is no point as this oven would have no problem doing a load in two hours at a temperature below where the wood ignites. As an aside, I have torrified wood in air, have worked on heating equipment like the oven in the video.

https://youtu.be/cv3cM0qQecY?t=75

On baking compared to torrified, the backed tops would have any pitch solidified, no changes to the wood otherwise. The Adkin video has them baking at 90 C. I have gone up to 120 C to bake tops.

Cooking tops has been around a long time. you may get them up to 200 degrees for hours and the bound moisture content is forced out while the gummie turpine resins dry out leaving a top that is very much cured and ready for use.

with nitrogen the temps are much higher. The effect on the material more extreme.

With Cedar tops it became clear that heating them caused them to die after a few years. I never heat Cedar.

My concern is long term, time and use create great sound. Some report to me that the high heat process causes noticeable differences in how the fibers respond to tools.

But if its creating an old sound in a new guitar people will want it. Some of these extra dense Tops people gravitate too will likely benefit.

It's the way they are made. The same for every guitar. It's not just one thing, it's all the things, every single thing, that Atkins does to make an instrument that delivers the 'Atkin's sound' - all manufacuting process are holistic, I don't know why everyone is so convinced that it's this one thing, or one specific other thing, that makes their guitar sound the way it does. Your guitar sounds the way it does because it's made by that maker, not because of any one thing or two things. IMO.

Heating them, does that mean below 100 C, above 100 C but below 180 C, above 190 C? Or are you talking Fahrenheit? Why does using nitrogen result in higher temperatures? The wood is more like driftwood after torrefaction, mind you baking for an hour compared to an hour and a half will give some of the benefits without the drawbacks. People dialed back the amount done as compared to a few years ago. Maybe the cedar was in too long? The glue up is a little more challenging, I have not found much difference with tooling.

I've thought the term "baked" was just a simplified term for torrefaction that some makers use. I and a couple shop owners I've spoken with over the years use the terms interchangeably. (Perhaps we're wrong...?) I have two torrefied guitars (one just the top, the other top, B&S, and braces). While different builders may have their nuanced approach to the process I was under the impression it's all done basically the same (high temps in an inert, oxygen deficit environment); other than the precise "recipe" of time and temps used to "dial-in" what the luthier wants. Again, am I wrong...?

I acknowledged that in my initial post, and wanted this thread to focus on baking vs torrefaction. Not sure my initial post should have elicited this response :confused:

In gelatin processing we used an evaporator. Gelatin is used to make capsules for medicines. Or glue for making guitars. :) The process seems very close to the torrefaction process. It is a process that boils off the water under vacuum leaving the unharmed and unchanged concentrated gelatin. It boils off the water at a lower temperature. The process is controlled. It isn't full on or nothing. I can easily see a computer handling the whole torrefaction process. Just load up the chamber and hit a button. The computer will flag you if anything goes out of line. With wood it could just shut itself off. Once the problem is straightened out it could be restarted. But I'm no expert.