Stability of Torrefied Tops

Frank Sanns
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Joined: Sun Oct 21, 2018 5:38 pm
Real Name: Frank Sanns
Location: Pittsburgh

Re: Stability of Torrefied Tops

Post: # 2008Post Frank Sanns
Thu Jan 09, 2020 4:27 pm

Maybe some background information of how torreffied wood started to be used in guitars would be helpful.

Over the course of a couple of years, Dana Bourgeois and I had discussions of what constitutes "aging" in a guitar. I am using this term generically and not referring to any one tonal, stability, or esthetic, properties. At the time, I had AO1 processed one of his Soloist guitars and he was intrigued by the result. The discussions continued as I was requesting a guitar with more potential rather than "all now" build. He made a statement that completely makes sense for him as a builder; that a customer wants a more mature sounding guitar out of the box and not one built to mature in years to decades. The quandry becomes, good instant gratification or stellar gratification after years or decades? It is a compromise as many things with guitars are.

At some point, Dana became aware of the torreffied wood and decided to do a build. I am NOT saying that I suggested torrefied wood. I did not. That was ALL Dana. I did have the opportunity to see and play the very first prototypes before they were announced and tp give my feedback. It is very much as I say today. The biggest effect is that it does not feel the same as a new guitar with the same build. it has a dryer, more percussive response. I affirmed with him that he had a winner.

Over the next year, we looked at lower temperature processes and adhesion and brittleness and many other factors. With two match sets cut from abutting wood cuts, two guitars were built to study the effects of some of the milder torrefication conditions. Unfortunately, apples can never be compared to apples. For Dana to tap tune the wood, the bracing and thicknesses had to be adjusted for each guitar. For this reason, it was not possible to to do a one to one comparison of some of the finer points. What came to be with the torrification was a compromise of physical properties, toughness (more on that in a moment), adhesion, tonal, visual, etc. (On a side note, during this period I also did a full evaluation of several different glues including hide glue on sound propagation and adhesion).

Now to the specifics. Baking wood removes some of the small molecules (plasticizers) that keep wood flexible and elastic. Water is just one of those molecules. Baking also breaks some chemical bonds that contribute to the overall strength and elasticity of the wood. While both of these make the wood stiffer and lighter, they both make the wood less elastic up to the point of being somewhat less tough and more brittle than unbaked wood.

A generality is that torrefied wood is more dimensionally stable long term. It will do better where the humidity is changing and hence will not change tone as much in a humid environment as a non baked guitar. Because the reduced cycling of expansion and contraction of the wood when moisture goes in and out, the baked wood should hold up better with time. On the other side of that is that the toughness of the wood is reduced when baked. A mildly baked piece of wood loses about 10%-15% of its strength so it should not be a factor for durability of a guitar. More heavily baked guitars may or may not be a good choice for rough handling and gigging though.

Early torrefied wood was overdone. It was crispy, brittle, and would crack on its own. No guitars were ever made from it but it was clear that being too extreme with conditions would give an inferior wood. This gave a good data point on the general properties of torrefied wood and helped find the proper conditions for the desired effects. If you notice, the guitars of today by just about all builders are a little less torrefied than in the first days and this is a very good thing.

Today, I think the torrefied guitar industry has matured and is making appropriately baked wood that should give long term stability and slightly less tonal changes with humidity.

It would not be proper to say that these are the same as old guitars as they are not. They are a different path to a different end.

I think torrefied wood should be looked at as just another choice in selections of woods. It should be chosen much like Adirondack, Engleman, German, Sikta, Torrified European, Moon spruce, Torrefied sitka would be chosen as a top wood. Different strokes for different folks.

Frank Sanns

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