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Minimum time to season tops
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Author:  grumpy [ Mon Mar 12, 2012 2:23 pm ]
Post subject:  Re: Minimum time to season tops

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.

Author:  David Malicky [ Mon Mar 12, 2012 3:37 pm ]
Post subject:  Re: Minimum time to season tops

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):

(source: page 26 of ... 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):

(source: page 10 of ... itTime.pdf )

Technically, these scanning curves also depend on the direction of RH change (adsorption or desorption) -- see figs 4 and 5 here: ... 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).
Sorption_Simpson_Anton TenWolde.jpg

(source: page 3-8 from ... 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?

Author:  James W B [ Mon Mar 12, 2012 3:37 pm ]
Post subject:  Re: Minimum time to season tops

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.

Author:  James W B [ Mon Mar 12, 2012 3:42 pm ]
Post subject:  Re: Minimum time to season tops

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:

Author:  John Arnold [ Mon Mar 12, 2012 9:59 pm ]
Post subject:  Re: Minimum time to season tops

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.

Author:  David Malicky [ Tue Mar 13, 2012 2:02 am ]
Post subject:  Re: Minimum time to season tops

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: ... 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):
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.

Author:  truckjohn [ Tue Mar 13, 2012 7:35 am ]
Post subject:  Re: Minimum time to season tops

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...


Author:  mqbernardo [ Tue Mar 13, 2012 11:44 am ]
Post subject:  Re: Minimum time to season tops

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.

Author:  pvg [ Tue Mar 13, 2012 12:24 pm ]
Post subject:  Re: Minimum time to season tops

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]

Author:  WendyW [ Tue Mar 13, 2012 1:04 pm ]
Post subject:  Re: Minimum time to season tops

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

Author:  Beth Mayer [ Tue Mar 13, 2012 3:31 pm ]
Post subject:  Re: Minimum time to season tops

+1 Awesome discussion! Beth

Author:  James W B [ Tue Mar 13, 2012 6:39 pm ]
Post subject:  Re: Minimum time to season tops

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?

Author:  grumpy [ Wed Mar 14, 2012 12:34 am ]
Post subject:  Re: Minimum time to season tops

We cook our sides when we bend then......

Author:  David Malicky [ Wed Mar 14, 2012 2:51 am ]
Post subject:  Re: Minimum time to season tops

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.

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.

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?

Author:  nickton [ Wed Mar 14, 2012 4:33 am ]
Post subject:  Re: Minimum time to season tops

I like that idea of making a solar oven in those hotter and dryer summer climates like Arizona. Maybe I'll buy a bunch of tops and make one for around here this summer. Eat Drink :idea:

Author:  Eric Reid [ Wed Mar 14, 2012 5:32 am ]
Post subject:  Re: Minimum time to season tops

Wow. Certainly one of the most interesting threads I've read. My thanks to everyone who has contributed. David, I am particularly grateful for your posts and links. Mario, your hands-on, work-in-the-field expertise made me pay attention, and keep reading. Todd, you're right, there's a lot of background to this. I'm busy catching up on my reading, thanks to your posts and links. Especially: Wendy. You touched a nerve. Thank you.

I want to cast out some random thoughts, and see what you all make of them.

David has brought up the important point that it's how much the wood changes ( shrinks, expands ) in the real world that matters. Okay, you bake your tops, and they're smaller when you're done. Are they more stable? Do they change less? I would have assumed that they are, that they do.

Even if they change less, are they stronger? USDA's old handbook #72 has some charts on wood properties after exposure to heat (immersed heat, steam heat, dry heat ). Brief dry heat (cooking tops?) seems to slightly increase the modulus of elasticity. Heat exposure just degrades modulus of rupture.

Maybe we're focussing on the wrong thing? Average values may not be what matters. Should we try to coax that extra 5% out of the top in hand? Or should we find another top that is 20% better?

I don't like ad. drivel. Perhaps if engineers wrote ad. copy, it would be as absurd as the marketing department's attempt at engineering:

"SPRUCE and EBONY are seasoned differently from our other tonewoods. After the stickering process, instead of being kiln-dried, the the wood goes into an oven, where it's baked at about 200 degrees (F...said C in original article, but typo...see post below for link) for about 2-3 hours."

"Ebony's extreme density makes it immune to cracking in the higher heat, and it won't shrink. It's also the most difficult wood to successfully dry - not because it cracks or warps, but because it doesn't lose moisture easily. Baking it facilitates the release of bound moisture"

Earlier, Taylor (it's his company) had explained that their default drying process involved a week of drying at temperatures that increased over the week cycle up to 270 F.

So, we've got this: "Ebony is immune to cracking, and it won't shrink." ( That's good to know. What should I call those open spaces in fingerboards? And, why do frets expand in dry weather?)

And: If ebony is so difficult to dry, how is 2-3 hours at 200F better than a week at temps up to 270 F?

Perhaps most importantly, why are we even talking about the nonsense that marketing departments spew?

Author:  Mike Lindstrom [ Wed Mar 14, 2012 8:19 am ]
Post subject:  Re: Minimum time to season tops

Another thread, by whom I don't remember made me wonder if anyone has experimented with baking phone saddles to create a similar dimensional stability.

Author:  James W B [ Wed Mar 14, 2012 8:46 am ]
Post subject:  Re: Minimum time to season tops

Grumps ,what about backs? Is this something worth considering?

Author:  David Malicky [ Wed Mar 14, 2012 5:16 pm ]
Post subject:  Re: Minimum time to season tops

Eric, you're very welcome! Good to hear it's helpful. I'm thankful for all the posts, too -- this topic has a lot of dimensions and it's great to have all the input.

On strength after baking, I ran across an old chart that plots degradation as a function of time and temp (Figure 1 here): ... llande.pdf
So 200F for 2 hrs shouldn't cause a loss of strength. There's a lot of recent work on "heat treated" wood (up to 400F for many hours)... IIRC those studies find strength and mass losses start around 300F. Maybe that's why Taylor doesn't go to 270F for tops.

The hysteresis effect does make a clear experiment difficult to do. But, re-reading the W&S article more carefully, it could still be correct about the 1 or 2mm movement, instead of 3mm for uncooked wood. They certainly know wood and have done real experiments; the above is virtual and sitka may behave differently than the FPL chart. Possibly, the 2mm and 3mm are what you get following the desoprtion curves, and the 1mm is from following a scanning curve. If so, a 1mm improvement (out of 3mm) is in the same ballpark as the 0.15 from the FPL chart, and worth it, at least in mass production.

To be clear, Bob T knows many times more about wood than I will ever know, and I have great respect for him. I actually learned about EMC after I showed him a prototype student-project guitar with a sunken top -- I was one of those engineers that had mostly done metalwork. He suggested cooking (which was too much work at the time) and drying the top before bracing (which has worked great for us). I try to upgrade the project every year and am thinking of cooking, thus all this figuring.

Author:  James W B [ Wed Mar 14, 2012 6:28 pm ]
Post subject:  Re: Minimum time to season tops

I thought I was not going to be building anymore and didn't put away any tops for future use. Now I want to build, so my question is...when you purchase tops from a supplier, how long is the minimum amount of time they should season in your shop before building? Thanks, Wendy. In regards to this which was the original question that started this post.I recently purchased a Wagner moisture meter and have been taking some readings.Some spruce tops that I just received were at about 9% .Some redwood sinker at about 15% .A tad damp for redwood I thought.I`ve also taken readings on some back and side sets and stickered them in rh controlled and dated them.It will be interesting to see the change over time.Some of the denser woods like rosewood are reading about 4%.1 set I just received,others have been in rh for quite some time.Not really much dif.The reason I wanted to know Mc was for new sets and tops coming into the shop.I figure if some of them have high moisture content.I`ll dry them a little slower before going into the rh room.Also of course ,this will let me know the mc before I build with it.I mean if it`s dry it`s dry I guess.

Author:  James W B [ Thu Mar 15, 2012 10:15 am ]
Post subject:  Re: Minimum time to season tops

Good tip Todd.Although I`ve had one of those charts in my rh controlled room for a long time.My shop is temp controlled but not rh controlled.All wood working procedures are done in the shop and all glue ups in the rh room.Everything always goes back in the rh room at the end of each working session.This is why I thought it would be interesting to know the mc of newely received wood.I`ve had a little trouble with some sets wanting to twist and warp when they go directly into the rh room when receiving them.With woods that I received where the mc is a little high,I`ve been advised to dry the wood in a more natural rh condition by stickering in the shop and weighting it down and blow a fan on it to bring the mc down before storing in the rh room for future use.I suppose there maybe a way to figure mc by weight and volume also,don`t know.I`m not sure if this thinking is even correct as wood reaching emc out in the shop obviously will be different than in the rh room,although I`m not sure how blowing a fan on it effects this,and this is where it will eventually wind up.I mean are some woods just doomed to twist? Any advise on this situation would be great.I do have a small scale for shellac mixing and such ,but not sensitive enough for real good accuracy.By the way I actually got my moisture meter free,because of some kind of points the wife gets on amazon.Although she probably spent a million bucks on stuff for the grandkids to get them. :cry: I hope this isn`t to far off topic,But I for one would like to know ,What is the best thing to do with recently acquired woods? and will knowing the mc when received even be helpful? Never had a problem with tops ,just back and side sets,and only a few ,but still the stuff is expensive.I think I`ll put a chart in the shop also.

Author:  SteveCourtright [ Thu Mar 15, 2012 1:26 pm ]
Post subject:  Re: Minimum time to season tops

Excellent posts everyone. Thanks for your contributions.

Author:  Joe Hill [ Thu Mar 15, 2012 2:24 pm ]
Post subject:  Re: Minimum time to season tops

You guys have raised questions in my mind along this subject line. I don't want my wood to crack down the road.

I live in Fla. so my situation would be a little different than Wendy or Beth. I have no basement, if I did it would be underwater. Humidity can go from 60% to 100% at any given time. I am just now starting my collection of tone woods. I keep it in the house where the humidity stays pretty much at a constant due to A/C. If I was to leave it outside would it get inundated with moisture? If I baked it what effect would this tropical climate have on the woods afterwards? Will my climate effect the seasoning time? I have noticed that the wood I used for carpentry, even if weighted warped hence I bought a lot of extra lumber.


Author:  nickton [ Fri Mar 16, 2012 2:41 am ]
Post subject:  Re: Minimum time to season tops

I wonder if you could use an iron to dry it out too.

Author:  truckjohn [ Fri Mar 16, 2012 6:21 am ]
Post subject:  Re: Minimum time to season tops

If you poke through the post... one of the things you don't want to do is to dry the outside super duper fast while leaving the inside relatively wet.. or heat it a giant amount on one side while the other stays cool... which is what a hot iron will do.... A clothes iron is a fine way to induce a permanent warp in a piece of wood... just like it can do in clothes...

For the most part - almost all the wood you are buying from Luthierie suppliers is already dried and seasoned at their shops... Sometimes for years... It's not coming in green... Literally - it only takes a week or 2 for a purchased set of thin plates to come to equilibrium with your workshop.... It does not take years... so unless you are gluing with hide glue and trying to warm up your wood - what does the iron help with?


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