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PostPosted: Sun Mar 11, 2012 10:49 pm 
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The 200 deg C was a typo, corrected to 200 deg F in a following issue. See bottom right of page 2:
http://taylorguitars.us/woodandsteel/is ... r_2009.pdf

Original article on page 27:
http://taylorguitars.us/woodandsteel/is ... l_2008.pdf

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PostPosted: Mon Mar 12, 2012 12:05 am 
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Those that want the facts need to probably find some scientific data that can be trusted and is reliable........... eveyone has an opinion.......... some right / some wrong. At one time a large section of the poplulation thought that the world was flat.

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr57.pdf if you search more you will find many books on the subject both as Federal Documents and State Document. I've never personally found one that recommends rapid cooking with out some other things going on......... like vacuum, moisture, heat control.( modern day vacuum kiln ) Other publications of intetest http://www.esp90.com/docs/fp.htm

Lumber on the roof under a tin for the day and the night cycles woudl be equivalent to our modern day solar kiln....... they are very effective and produce a good stable piece of material if a schedule is followed.......... it is fairly slow. Federal information ia available free to build such a kiln if you have and interest.

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PostPosted: Mon Mar 12, 2012 9:20 am 
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For me there`s just not enough proof that baking tops has any long lasting advantages.I for one won`t be cooking any wood without knowing what the ACTUAL moisture content of the wood is even though I may ASSUME that the wood has reached EMC.Heck, I wouldn`t do it if I did.It just goes against my gut feel.Maybe that`s why I haven`t fallen off the edge of the world.I`ve never been one to do a thing just cause others do.As far as sound goes,it would be interesting to put a couple of cooked top guitars in a line up of say 10 and do a blind listening test.I`ll bet it would be impossible to consistently pick these guitars out of the bunch as better sounding.This seems to fall right in line with the idea that some guitars made with different glues sound better than others. I personally have used different glues and I can honestly say I can`t hear it.Although I do wear hearing aids. :lol: So to be honest ,I`m not the best judge for sound. I have had a few people who own Taylor guitars tell me that mine sound better,as probably many guitars built by forum members do.Not to bragg,but there are some amaziningly talented people on this forum,and I know I`m not anywhere near their level.Your right though Todd this is an interesting topic.I`m just not sure there`s enough scientific data to reach a conclusion one way or the other on it regardless of how many bake and how many don`t.I do know there are more time tested ways to get well seasoned ,stable wood for guitar use as Kevin states.I guess I`m old school.What do you expect from an old guy.
?
James :)

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PostPosted: Mon Mar 12, 2012 10:30 am 
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James, "baking" tops isn't about better tone, and I for one haven't heard a difference between my baked tops and those that weren't.

"baking" tops is about crack prevention. When we take wood down to 0% MC(IE: bone dry) and hold it there for a while, the wood will shrink to its absolute minimum dimension, and it has been found that the wood never returns to its previous dimensions when it comes back to EC. It's an easy enough test for you to do, if you so wish; take two consecutive slices from -one- guitar top offcut(should be able to get 2 one inch slices), bake one overnight at 212°F, then compare them. Let it rest a few days to return to EC, then compare again. You'll find the baked slice will never return to its full length. Basically, what this does is "pre-shrink" the top, such that if the guitar is exposed to a very dry environment, it is much less likely to crack because it is already quite close to its minimal dimension.

In other words, it's not magic, nor a wives' tale, but solid science. And rather common sense.

And it is very different from kilning.

No need for 36 hours, either. I once worked in a pulp lab, and we dried soaking-wet and green spruce chips 12 hours in a convection oven at 212°F to bring them to 0%MC. Not because we thought it was enough time, but because TAPPI, the pulp and paper industry think-tank did the studies and deemed 12 hours to be plenty. We did our own tests, to see if we could dry for shorter periods when/if we needed rushed results, and using a scale with a resolution of 0.0001/G(4 decimal points to a gram), we couldn't detect any further drying after 6-7 hours. These chips were 2 to 3 times thicker than a guitar top, too. So with that in mind, I never bother baking longer than overnight. And there's no benefit to using temps higher than 212°F, and plenty of chances to induce case-hardening if you do go over 212. You won't see any case-hardening from a 12 hour cycle at 212°F.


Last edited by grumpy on Mon Mar 12, 2012 10:41 am, edited 1 time in total.

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PostPosted: Mon Mar 12, 2012 10:36 am 
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Now that's good information! Never thought of it that way. Thanks, Mario!

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PostPosted: Mon Mar 12, 2012 10:43 am 
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You're welcome!


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PostPosted: Mon Mar 12, 2012 11:29 am 
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This is a crazy thread. Why have I not read about this in Cumpiano or Gibson's book on guitar building?

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PostPosted: Mon Mar 12, 2012 12:28 pm 
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That is good info Grumps.I`m with you on the sound thing.I was just commenting on what Darryl said about that old instrument dry sound.And trying to add a little humor.Note the laughing head.Sorry Darryl ,no harm meant.Although I do have a couple of questions,in interest that I may try this at some time.How did you determine that the wood was taken down to 0% MC.Was it weight or shrinkage?I`m just guessing here,or do you have some other recognized means of measuring this? Obviously common sense does say the wood is dryer.Also how sure are you that this won`t effect wood in any other adverse ways.That`s my main concern.I respect your judgement as a very fine Luthier,so not trying to make a fuss.Like Todd said I`m just trying to rap my head aound it.So
Peace,
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PostPosted: Mon Mar 12, 2012 1:28 pm 
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This probably isn`t anything to worry about.Thought I`d throw it out there.Stage 2 and Stage 5 mention wood that is too dry.Not sure if this applies in this case?I sure I don`t have a clue about this stuff. :?
James
GLUING, LAMINATING, AND VENEERING FAILURE

One of the major areas in furniture manufacturing that causes problems is gluing-edge gluing, laminating, and veneering. There are at least 100 things that could be wrong when a glue joint is below par. But, as a general rule, a gluing problem is a breakdown of one of the five "links" in a glue joint.

The adhesive, or middle link (#1), is determined by the strength of the adhesive itself. If the proper adhesive has been chosen and handled correctly, this link shouldn't be a problem. The next links (#2 and #3) represent the bond between the wood and the glue. In practice, weakness of this bond is the most common cause of glue-line failure. Weakness results because the adhesive cannot attach itself to the wood. Two common reasons are: (1) the surfaces to be glued are several hours old and have become less active because the glue-bonding sites are occupied with dust or with moisture from the air; and (2) the wood MC and the EMC aren't close enough, so the wood changed MC, swelled (or shrank), and now the surfaces are no longer perfectly flat (0.002" to 0.006" is the preferred gap between surfaces-no more or no less for maximum joint strength). Links #4 and #5 are the wood surfaces themselves.



GLUE-LINE FAILURE

There are five stages in forming a good glue bond. The key to several of these stages is proper wood moisture. That's why metering is important.

STAGE 1:

After application to the wood face, the adhesive must flow to form a fairly smooth, continuous film. It won't flow if it's too thick, if the wood's too hot or too cold, if the wood surface is dirty, or if there isn't enough adhesive.

STAGE 2:

The adhesive must transfer to the opposite, mating surface. This requires pressure and sufficient adhesive. Excessive assembly time or wood that is too dry can cause a failure in this stage. Lack of sufficient pressure and precuring are also common causes.

STAGE 3:

The adhesive penetrates the microscopic nooks and crannies of the wood surfaces with the application of pressure. Pressure also pushes the two pieces within the required 0.002" to 0.006" gap. Too much pressure squeezes out too much glue which is a weak glue line; too little results in a thick glue line, which is also a weak glue line (except for gap-filling adhesives).

STAGE 4:

Good glue joints are characterized by good "molecular" bonds between the molecules of the wood and the adhesive. For this bonding to occur, the wood and adhesive must be in intimate contact. However, sometimes the wood surface is contaminated or is chemically unable to bond. This is called a"non-wetting" surface. (Imagine trying to glue two pieces of wood that have oil on their surfaces.)

STAGE 5:

The final stage is the solidifying of the adhesive. Failure to solidify may be caused by cold temperatures, pH problems, or adhesive/catalyst problems. The rate of solidifying is influenced by the wood's moisture content (the drier, the faster) and by temperature (the hotter, the faster). Lumber that is too dry withdraws water before all five stages are completed.

A final note on gluing. There are a considerable number of factors in the gluing operation that affect the strength, durability, and appearance of a glue joint: (1) factors relating to the adhesive itself; (2) factors relating to the handling of the adhesive from its arrival in the glue room until it is applied to wood, pressed, and heated; and (3) factors relating to the wood itself.



CRACKED OR CHECKED FINISHES

This is a frequent complaint. When today's finishes dry, they become quite rigid. Any expansion or contraction of the wood underneath causes stress which can lead to cracking and checking of the finish. Correcting this problem requires maintaining an EMC in the plant equal to the in-use EMC, and achieving and consistently maintaining the MC of the wood that is equal to the EMC in-use.



The above information was originally prepared for the report entitled:
10 Ways of Eliminating Wood Problems
Dr. Eugene M. Wengert
Extension Specialist, Wood Processing
University of Wisconsin-Madison, Department of Forestry

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PostPosted: Mon Mar 12, 2012 1:33 pm 
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James, the thing that convinced me into baking tops years back, was by taking a well seasoned top at EMC @ 70 degrees and 40% RH and accurately measuring 6" across the width of a top half and draw a line parallel to the length. Then bake for a couple hours @ 200 degrees. Then let the top half sit in the shop for a week or longer @ 70 degrees and 40% RH so as to reach EMC. Now remeasure the distance from the edge to the line, it will be less than 6". It will not expand back to its original size in the same environment.

Chuck

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PostPosted: Mon Mar 12, 2012 1:38 pm 
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No problem James........I'm used to being made fun of! <smile> Please note I stated I was speculating about artificial aging making the tone better.

Also, I still can't vouch about for elevated temperatures removing moisture from inside the cell wall that never returns.......but the therory seems to go along with what some are stating above.....so it's still a possiblilty.

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PostPosted: Mon Mar 12, 2012 2:23 pm 
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How did you determine that the wood was taken down to 0% MC.Was it weight or shrinkage?

In the lab, we measured it by weight.

But it's much, much simpler than that. Water boils at 212°F. An environment that is maintained at 212 for a length of time will drive out ALL moisture(IE: water). That is also why 160°F for 36 hours still won't take it to 0%MC; close, but not quite there.

A forum member wrote me directly just now and asked if we should bake archtop wedges, and do I bake my mandolin tops? The answer is no, to both. Yes, the thickness will cause issues, because baking to drive-out all the moisture from a 3/4" thick or thicker piece can't be done quickly and evenly enough; you'll end up cooking the outside while trapping moisture inside. Not good! That's where kilning comes-in(pay attention, James), and where kilning is not baking, and baking is not kilning. In a kiln, moisture is ---added--- into the kiln during the drying process, so that the outside of the wood doesn't dry faster than the inside, which would cause all sorts of issues, fractures, case hardening, etc... But a piece of spruce that is only 0.120 to 0.140" thick doesn't have this issue, and can be safely baked. For that reason, I would not advocate baking bracewood, either. Nothing to gain there anyhow.

Also, archtop plates, be they mandolin, guitar, whatever, aren't as prone to splitting as a flatop guitar, because the arch can and does move with the seasonal fluctuations. It's also why they almost always sport adjustable bridges, because the top will rise and fall with the RH.

One last thing; guitar making is not furniture making. Do yourselves a favor, and separate the two.

EDIT: I still can't vouch about for elevated temperatures removing moisture from inside the cell wall that never returns.

The moisture does indeed return, but the cells never swell back up to their original size.


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PostPosted: Mon Mar 12, 2012 3:37 pm 
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Great thread. Todd, that's very interesting, on the sap differences between 160F-36h schedule vs 200F-2h -- thanks.

As Todd, Mario, Chuck, and others have found, getting the wood down to 0% EMC does permanently change its response to moisture from that point forward. As many of you know already, the wood science folks have some graphs for this effect, called the desorption-adsorption curve (the y-axis is moisture content):
Attachment:
Sorption_Sehlstedt-Persson.jpg

(source: page 26 of http://pure.ltu.se/portal/files/199184/ ... 570-SE.pdf )

The dotted line shows the first time the wood is dried to 0% EMC. The bottom line shows what happens as the wood re-absorbs moisture (adsorption): at a given RH, the wood has less water in it and for RH < ~50%, the wood is less sensitive to RH changes (the bottom line is a bit flatter than the dotted line). If RH is increased to 100%, the wood eventually absorbs as much moisture as it started with. But then, as RH is decreased from 100% (the middle line), the wood loses moisture faster than it did before any treatment was done, and always stays at a lower EMC from that point forward.

Of course, most luthier wood (hopefully!) never gets back to 100% RH. In that case, the wood traverses between the adsorption and desorption curves, along what are called "scanning" curves (the dotted line (4) in this next fig -- sorry it's hard to see, click to enlarge):
Attachment:
Sorption_Berit_Time.jpg

(source: page 10 of http://www.ivt.ntnu.no/docs/bat/bm/phd/ ... itTime.pdf )

Technically, these scanning curves also depend on the direction of RH change (adsorption or desorption) -- see figs 4 and 5 here:
http://www.scielo.cl/scielo.php?pid=S07 ... ci_arttext
Fortunately for luthiers, these scanning curves tend to be pretty flat. So if RH is controlled reasonably tightly, the wood may see very little change in EMC.

Since RH changes are in random directions outside the lab, many plots just show an "oscillating" sorption curve. But this is more of a "likelihood" curve, as it ignores the very real hysteresis effect (EMC depends on both the RH and the recent RH history).
Attachment:
Sorption_Simpson_Anton TenWolde.jpg

(source: page 3-8 from http://www.fs.fed.us/ccrc/topics/urban- ... 20wood.pdf )

So, getting the wood to 0% EMC is a good thing. But there are still lots of questions (maybe already answered by some other wood science or luthier lab -- I don't know)...

1. After a 0% EMC treatment, how do the dimensional changes vary with EMC? We know the wood is shrunk, like Chuck and Mario said. Is that only because its EMC is lower (not on that "initial desorption" curve any longer), or does it also expand and contract at a different rate relative to its EMC? That is, is the "inches movement per %EMC" coefficient the same or different? The common assumption seems to be that the coefficient is the same, but I don't know of any evidence either way.

2. How close to 0% does the wood have to get to show the full effect of the treatment? Would old wood, having likely seen 10% RH in its life, also show the effect?

3. What effect do the various drying schedules have? For example, 160F in a desiccator for 36h, or 200F for 2h in an oven, or 220F for 1h in an oven. That is, how does temp affect the wood properties apart from the 0% EMC effects?


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PostPosted: Mon Mar 12, 2012 3:37 pm 
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Grumps ,I`m gonna go ask the wife if I can borrow the oven. [uncle] And yes, guilty as charged.I`ve built a bunch of furniture.
James

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PostPosted: Mon Mar 12, 2012 3:42 pm 
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David good post very interesting.I promise not to throw any wood in the bathtub.David ,what part of San Diego?I was raised there.I know off topic.
James :lol:

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PostPosted: Mon Mar 12, 2012 9:59 pm 
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The bowing that can occur to thin woods that are dried too quickly is due to the edges drying faster. That is different from the common definition of casehardening, where there is differential moisture content through the thickness of a board during the drying process.
Casehardened boards will bow when they are resawn.
Thin hardwoods (particularly plain sawn) are more susceptible to bowing, so I like to air dry them to 12% moisture content in board form before resawing.
Gallagher Guitars has been baking their tops since the 1960's, and Martin would bake their BR in the old days.
In cutting red spruce for instruments, I took the opportunity to check pitch pockets, just to see how long it took for the resin to crystallize without baking. The average time is about 2 1/2 years, with some examples hardening in a little over a year.

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PostPosted: Tue Mar 13, 2012 2:02 am 
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Interesting info, John, thanks.

James, glad it was helpful. I'm in the Clairemont area... moved here about 7 years ago from KS, no plans to leave!

On whether baking improves tone, there might be a slight advantage via the lower EMC -- a bit less mass, and probably less damping. Probably tiny for both, though.

Reading more in one of the prior links, I found an answer to my question #1, from a 1976 study on pine. Basically, no difference between air dried and baked (up to 93 deg C) for the % movement per % EMC coefficient. Page 35: http://pure.ltu.se/portal/files/199184/ ... 570-SE.pdf
To lower the coefficient, it looks like the wood has to be "heat treated" (~200 deg C), which also shifts the whole sorption curve down. For example, compare Figs 4A and 5 (separation is greater in Fig 5):
http://www.bfafh.de/inst4/43/pdf/heat_net.pdf
So, that Taylor typo actually has some benefits, including less mass, but it also degrades strength by ~15%. I wonder what it does for damping.

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PostPosted: Tue Mar 13, 2012 7:35 am 
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Drying wood from green is a very different discussion vs what we are talking about... We are really talking about acclimating wood that's already "Dry" to your workshop.... so while issues like case hardening and honeycombing are real concerns - even when air drying wood.... Unless we are milling our own trees - by the time the wood gets to us - that sort of thing is usually sorted out....

You will find wood move around whenever you move it from 1 climate to another climate... It doesn't matter how old it is or how long it has sat around.... Take a 3,000 year old Spruce top set out of the Pharoh's tomb and bring it here in the winter - and it will twist and cup and move around until it settles down and flattens out again....

Now, there are 2 different discussions going on here... The 1st is about how long does it take to dry the wood from wet till it's at equilibrium... In the case of our thin wood sets - not very long... Literally, you can go from green to 7 or 10% emc in a couple weeks....

The 2nd discussion is about letting it sit and stabilize.... I think this is more a question of being able to observe it's response to environmental change....

For example - I have an African Ebony fretboard billet blank, BEAUTIFUL pure black ebony... It was old when I got it.. and it's been sitting in my closet indoors for 5 years now... Every spring and fall - it kinks at one end (No cracks - it just kinda bunches up into a funny Z type pattern)... and every summer and winter, it flattens back out again.... I can't use it unless I can figure out how to cut off that whole end.... I would never find that out if I just bought it and put it into service....

Other cases of tops I bought from re-sellers that were obviously OLD and had sat around a while... I opened the box and put the tops on a little rack to watch what they did for a day or 2 while they settled down... Once I was happy that they weren't mis behaving too badly - I jointed them and built with them... No problems.

So... Sitting around for a long time could potentially let you observe which wood is going to spring a trap upon you and which will sit there and cooperate nicely.... but that doesn't mean it's not dry and could not have been used sooner...

Thanks


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suppa-thread with much food for thought, thanks guys!
Incidentally, lately i´ve been pondering about the effects of seasoning on wood, so this will be a timely read.

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PostPosted: Tue Mar 13, 2012 12:24 pm 
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Well Wendy, quite a discussion ensued from your seemingly simple and innocent question!! :D
By and large, this has been a very instructive and thoughtful discussion; thanks to all who contributed their views. This thread shows that intelligent choices are based on knowledge; and that forums (fora?) like this are invaluable resources for developing a knowledge base.
Obviously one has to do a bit of sifting through the discussion to extract the information relevant to his/her own needs; but I want to compliment the forum members on the high quality- and usefulness- of the contributions made here.
[clap] [clap] [clap]
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PostPosted: Tue Mar 13, 2012 1:04 pm 
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You're right pvg, I got my question answered and then some. I have been following along and have gotten a huge amount of useful information, both to my original question and then much more. This forum and the people here are amazing. Wendy


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PostPosted: Tue Mar 13, 2012 3:31 pm 
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+1 Awesome discussion! Beth


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PostPosted: Tue Mar 13, 2012 6:39 pm 
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So if it`s cool to cook tops .What about backs and sides?i`ve personally never had a top crack on me .KNOCK on wood,and keep my fingers crossed, but I have had a back crack about 3 months after it was delivered to the customer.Will cooking backs and sides help them from cracking also ,or are most of these woods to dense for this?
James

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PostPosted: Wed Mar 14, 2012 12:34 am 
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We cook our sides when we bend then......


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PostPosted: Wed Mar 14, 2012 2:51 am 
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Good posts and links, thanks.

The concepts have been looking so good, I ran some numbers. I scaled the last sorption graph (from FPL) in Autocad and measured how much improvement in EMC would occur from cooking tops. If we stay on the desorption curves (no 'scanning' / hysteresis), the improvement is pretty modest. :| Here's a virtual apples-to-apples test:
- Start with un-cooked wood at the blue 1, and dehumidify down the "Initial desorption" curve.
- Check EMC at 60% RH and 30% RH. Difference = 5.9% moisture.
- Cook to 0%, to the blue 2.
- Humidify, following the "Adsorption" curve, to 100% RH (red 3) (Anything greater than ~90% RH would probably work.)
- Dehumidify down the regular "Desorption" curve.
- Check EMC at 60% RH and 30% RH (red 4). Difference = 5.0% moisture.
Attachment:
Sorption.1234.jpg

Net improvement = 5.9% - 5.0% = 0.9% moisture, or as a ratio, 0.9/5.9 = 0.15 (I won't say 15% since EMC is also in %.)
Wood_Contraction = (Constant coefficient of contraction per EMC) * (Change in EMC). So if an uncooked top contracts 0.100", a cooked top would contract 0.100 * (1-0.15) = 0.085". Helpful, yes, but I imagine most of us expected something else.

Of course, no one rehumidifies their top to 90% or 100% RH. Say we try this virtual experiment:
- Same initial steps, but instead of humidifying back up to 100%, stop at 60% RH (the red 3' in the pic below).
- Check EMC.
- Dehumidify to 30% RH. This step will follow the 'scanning' curve from 3' to 4.
- Check EMC. Difference = 3.3% MC. This gives the impression that cooking tops is great: 3.3% is a lot less than 5.9%. But it's apples-to-oranges: it mostly exploits the hysteresis between the curves. Uncooked wood exploits hysteresis and follows scanning curves, too, after just one experience of reasonably low RH. Those of us that have cooked samples have found they are indeed quite a bit shorter than before cooking, but I don't think that measures what matters to a top in-service.
Attachment:
Sorption.Scan.jpg

Real guitar wood probably spends most of its life in the hysteresis zone, which makes designing an apples-to-apples physical experiment more challenging. Ideas?


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