[jdietrich]

Torrefaction (more properly, thermal modification) involves higher temperatures than kiln drying, causing chemical changes to the wood that result in permanently lower equilibrium moisture content and hygroscopicity. It improves the stability of wood and drastically improves the resistance of softwoods to decay, but it isn't a complete solution to wood movement. There is a significant tradeoff between stability and strength.

https://en.wikipedia.org/wiki/Thermally_modified_wood

[abakker]

It also changes the color, which in many cases is inappropriate for the project. However, if it were being painted I would definitely consider it. I bought some Torrefied ash recently - it's weird stuff. Kind of like working with toast instead of bread. the sawdust smells odd, too.

[nemo44x]

In the acoustic guitar world, torrefication has become popular for some guitars. The main idea is that the end result of the spruce (commonly used for top wood on an acoustic guitar) is closer to a piece of spruce that is many years old which affects the tone and "improves" it to some ears. The other benefit is the wood is less likely to crack which is an issue with acoustic guitars, especially in dry climates where humidification is an issue. Some say the wood is more resistant to cracking but more brittle in other ways which aren't too important to how an acoustic guitar applies tension. the main idea is the wood won't change with respect to humidity as much as untreated wood.

But yes, especially when luthiers started using this technique there were all sorts of issues with the end result in terms of superficial results/coloring. However, they've gotten better at this and now we see the wood being a bit darker but without all the other cosmetic issues from past years.

[jdietrich]

>The main idea is that the end result of the spruce (commonly used for top wood on an acoustic guitar) is closer to a piece of spruce that is many years old which affects the tone and "improves" it to some ears.

Torrefied tops can definitely make an instrument sound better. With the right thermal treatment, you get a slight increase in stiffness and a fairly significant reduction in damping due to the lower equilibrium moisture content and the depolymerisation of hemicelluloses. If the top is properly braced to account for the different properties, you get a more open-sounding instrument with more volume and/or sustain. Torrefied necks are substantially more stable, particularly for the flatsawn maple necks on most Fender-style electric guitars. The durability of tops is very much swings and roundabouts - you gain a fair bit of stability with respect to atmospheric changes, but the top becomes weaker and more brittle, so more prone to impact cracking.

>But yes, especially when luthiers started using this technique there were all sorts of issues with the end result in terms of superficial results/coloring. However, they've gotten better at this and now we see the wood being a bit darker but without all the other cosmetic issues from past years.

If anything, the caramel colour of torrefied maple or spruce has become a status symbol. We're starting to see a lot of roasted ash bodies on electric guitars and basses, which doesn't really do anything tonally but looks cool.

[nemo44x]

I agree, the slightly darker top is nice to my eye and gives it a fine head-start to the natural aging process of yellowing the guitar.

I think some of the issues that were out there with regards to coloring were things like "racing stripes" where there would be significantly darker stripes of darkened color an inch or more wide that would run up the tops, which many people disliked. It never really bothered me too much, personally.

I agree on the improved tonal characteristics - the reason I say "improves" in quotes is that this is entirely subjective. Some people are very sensitive about these types of proclamations for some reason. I believe it does make for better tone, which is why I have a guitar with torrification (red spruce top) being built currently. To my ear it is louder and more articulate than the same species of spruce that hasn't been torrified. As you've said, it's opened up right from the start rather than waiting years for the wood to change enough to create that open sound.

Of course when it comes to the tone of the top wood, besides the bracing (which is obviously unbelievable important), I believe that the finish matters a lot and as thin a nitro finish as possible is ideal. I've drank the kool-aid with regards to hide glue as well. At the very least, it makes a neck reset (dove tail, glued joint neck) or any other type of surgery easier in the future.