Baked Spruce Top?

[printer2]

Originally Posted by redir

Yes Atkin it's interesting. I'll have to give it a go on the next one.

So why stop at the top then? Or do you bake the back and sides as well?

I just left my sides in the bender nice and toasty. The back could be done in the oven also I guess.

[rick-slo]

Prior thread on the topic

http://www.acousticguitarforum.com/f...d.php?t=334818

[Lespaul123]

I wrote a paper in college about this. It was for a stats class and I planned on doing the test anyway so I decided to write a paper based on my findings. I cut up one top cross grain to 3/4 inch wide strips. I numbered each strip. I then put the strips in a room with a maintained humidity of 40% and allowed the acclimate and flatten out. After that, I humidified a separate room at 60% RH. I then took the strips and placed them flat on a table allowing moisture to only be able to absorbed on one side, thus causing them to curl. I measured the curl on all of the pieces and recorded the data to their corresponding number. I then deflection tested all of the strips and recorded them again to their corresponding number. After that I placed them in an oven at 180 degrees for one hour. I also made sure to keep them flat as instructed by others who bake their tops. I placed the strips back in the 40% room and allowed them to acclimate and flatten out as done before. I took the now baked strips into a room of 60% RH and placed them on a flat table. I should note that the time of curl measurement was kept the same between the two samples. After the set time I measured the curl and deflection tested all of the strips and recorded to their corresponding number. My findings were that the baked strips did curl less than those who were not baked. I did however find that the strips deflected on average more than those that were not baked. I will say that my deflection rig was pretty humble and I will probably retest this someday with better equipment. This is also only testing cross grain stiffness and not long grain stiffness. I wanted to keep the amount of variables to a minimum.

-Rob

[DanSavage]

I would really like to get my hands on some torrefied spruce for a guitar, but so far I've been unable to locate anyone who will sell me any. I can buy a completed guitar, but not just the wood to use to make my own guitar.

The process for producing torrified tonewood is pretty much the same one patented by Yamaha as their Acoustic Resonance Enhancement. (A.R.E.)

If you want the technical details, see Yamaha's US Patent 6,667,429 (Method for manufacturing modified wood).

Basically, the tone wood is put into an autoclave and the pressure and temperature is brought up to between 0.2 to 1.6 MPa (atmospheres) at 180C and then the wood is cooked for up to 60 minutes. The temperature and pressure are gradually brought down to normal to prevent the wood from cracking due to thermal shock.

From: Yamaha A.R.E. Technology.

Typically, wood is made up of fibrous cellulose and resinous lignin as well as a substance known as hemicellulose that binds these together. Old wood, in which the cellulose has crystallized, hardens in the direction of the grain. On the other hand, the amount of hemicellulose decreases, thus making it easier to remove across the grain. As it becomes harder in the direction of the grain, wood becomes softer across the grain. Materials that have properties that vary depending on direction are said to display anisotropy, which in the case of wood progressively improves sound as anisotropy increases. In other words, wood has strong characteristics, responding well when an instrument is played, extending the low range, and rapidly decaying the high range. Emphasizing the qualities displayed by matured wood resulted in the development of A.R.E.

For the A.R.E. treatment, wood is first placed in a cylindrical metal pressure vessel, the internal temperature and humidity of which is controlled as the treatment process is carried out; the pressure is changed in stages. This enables the treatment process to be undertaken in a surprisingly short time if compared with the time needed to age wood.

Of particular necessity during the treatment process is the precise control of temperature, humidity, and atmospheric pressure, as well as setting the optimal amount of treatment. The result of experience and expertise spanning many years, the optimal value settings combine the “sweet sound” of a musical instrument and durability, the wood being treated during a precisely controlled process.

From: Bourgeois Guitars’ Aged Tone Series

“The wood is essentially cooked at a low temperature in an oxygen-free environment. There’s more to it than that – it’s pressurized, they use steam at some point in the process – but the idea is that all of the volatiles in the wood get cooked off. The sugars, the resins, the oils – over 100 years, that is all going to be gone [naturally], but this speeds up that process. What you end up with is a spacious, resonant, dry sound that requires very little break-in time.”

“Torrefaction leads to a maturing of the wood where the wood gets stiffer and more responsive,” adds CEO John Karp. “The end-effect [when used in guitar manufacture] is it sounds more like an older guitar. It’s really not like a new guitar…”

“This material that gets cooked away [through torrefaction] has the effect of dampening vibration,” Bourgeois explains. “Once it’s removed, the top is able to vibrate more freely. It’s more resonant… it has a higher velocity of sound. It’s also lighter, so you end up with a greater stiffness to weight ratio, which is what you’re looking for in a top, anyhow.”