Sign in to follow this  
TedN

kiln dried wood

Recommended Posts

I purchased some tonewood from a supplier, but it feels very dry to me. Is there a way to tell if wood has been kiln dried?

If I can find out that it has been kiln dried, should I still make a violin from it? Does it make a lesser quality instrument?

Share this post


Link to post
Share on other sites

I don't think there's any way to tell for sure if wood has been kiln dried or not.  With the winter weather, there are many possibilities for wood to be extremely dry without involving a kiln (but I'm not sure if I could tell dryness by feeling it).

There are undoubtedly purists who will only use air-dried wood, but that is more of a personal aesthetic, I think, rather than a proven advantage.  I use wood that could be described as dried in hell, and it works fine for me.

Share this post


Link to post
Share on other sites

I had used wood from this particular seller before and my teacher suspected that it was kiln dried. The reason was that the ribs were impossible to bend. They always snapped. He couldn't even bend them, and he's an expert. I wonder if this is a characteristic of kiln dried wood? I wonder if the kiln drying somehow impacts the flexibility of the wood.

Share this post


Link to post
Share on other sites

Normal kiln drying temperatures shouldn't do anything to the wood properties, other than removing the free water in the wood.  I suppose if the kiln drying was done poorly, or at high temperatures, it could do something.  

I process maple to far higher temperatures than would ever be achieved in kiln drying, and it can still be bent (although it IS more difficult to do).

Share this post


Link to post
Share on other sites

There are a number of different methods for accelerated drying of wood, but the principal ones are a heat and vent kiln or a vacuum dryer.

With heat and vent, you can take it slow or fast, and you can determine the temperature and control the moisture content within the kiln by venting o by introducing steam. If the process is too rapid, you will end up with case hardened wood which would be inappropriate for violin-making because of the unrelieved tensions and the damaged structure.

Not sure if case hardening is an issue with vacuum drying - shouldn't think so.

But correctly kilned wood has exactly the same properties as air-dried wood as Don says. Mainly it feels different to air-dried wood because it's .... dry.

 

Share this post


Link to post
Share on other sites
4 hours ago, martin swan said:

Mainly it feels different to air-dried wood because it's .... dry.

After a couple of months, the EMC should stabilize to about the same with either wood.  

I'm not an expert on commercial kiln drying, but I wouldn't think that the goal is to get the wood extremely dry... just to safely remove the free water and get the EMC down to a reasonable level.

Share this post


Link to post
Share on other sites

 A kiln is simply a tool for controlling drying conditions. While I think the cycling of wetter to drier conditions involved with air drying is beneficial for tone wood the correct use of a kiln to reduce surface moisture at the start of the drying process is often extremely valuable in reducing stain and preventing the start of fungal infection. As Martin said the overly rapid reduction of moisture content can lead to case hardening or checking including micro checking which while invisible is certainly not what we want in tone wood.

Regardless of how the moisture content was reduced there are other aging processes involving changes in resins and other factors which are very important in the processing of good tone wood and the kiln may shorten the drying time a bit but I don't use wood unless it;has been in my shop for years.

Share this post


Link to post
Share on other sites

Worth remembering that dendro has revealed a tendency amongst the great Cremonese makers to use wood which was so fresh it was still wriggling ... but of course most of it seems to have spent quite a lot of time in water which speeds up drying, and Italian summers are hot and dry ...

 

Share this post


Link to post
Share on other sites

Thanks for all your replies!

Martin, when you say " But correctly kilned wood has exactly the same properties as air-dried wood as Don says. Mainly it feels different to air-dried wood because it's .... dry. " Do you mean that perhaps air dried wood may still be retaining some of the moisture, whereas, kiln dried wood is totally, totally dry. Like desert dry?

I wonder if  it's too dry, if that impacts the instrument.

The wood I have feels like saltine crackers it's so dry.  Other air dried wood that I have, feels dry, but you can tell there's some moisture in there still. Kind of hard to describe I guess.

Air dried wood is sealed on the ends with wax while it still has some moisture content within the wood. I'm not exactly sure how the moisture escapes the wood cells, but it must escape eventually by osmosis I presume. I wonder if the water escaping through the wood cells somehow relieves tensions within the wood?

Share this post


Link to post
Share on other sites

The sealing of the ends is purely to help prevent end checks - the ends of the wood tend to dry much more quickly. SOme people do this for air drying, some do it for kilning.

As someone who used to do a lot of commercial wood processing (many trees at a time) I never bothered with this. The wood it saved (hardly any) didn't equate in any way to the cost of the time involved. 

If you have one nice log from your garden then maybe it makes sense, but I'm dubious.

For the other part of your post, yes it's possible to kiln wood until it's dryer than the atmosphere around it, but as Don says it will take up moisture and reach EMC in a couple of months tops unless the structure has been damaged by the kilning process.

Share this post


Link to post
Share on other sites
2 hours ago, TedN said:

The wood I have feels like saltine crackers it's so dry.  Other air dried wood that I have, feels dry, but you can tell there's some moisture in there still. Kind of hard to describe I guess.

We don't have any built-in sensors that can detect dry or not dry... it's an interpretation of things like density, coolness, perhaps some surface stiffness.  And the moisture in wood isn't like a damp dishrag, but bound tightly into the wood fibers.

I suspect that a low-density piece of wood might seem more dry due to its lightness and better insulating qualities that don't draw heat out from fingers or hands when touching it.  If you can find a moisture meter, it would be interesting to see what it reads.  Or just see if it is lower density than the others.

Share this post


Link to post
Share on other sites

Well, if you felt grass clippings that were freshly cut and grass clippings that had been backing in the sun all summer, you'd be able to tell which one had moisture content and which one didn't, with a blind fold on. One is crisp and one is more malleable. I think you can do the same with wood, to some degree.

...

Yes, but isn't it all connected? You seal the ends of the wood to prevent air checks, but the reason the air checks form (I believe) is because the wood is drying out unevenly? I think that's the cause of air checks, but I could be mistaken. But then when you seal the ends, the moisture gets stuck within the wood, (kind of like sealing the ends of a straw) and the only way for it to escape is to permeate through the wood cells. That, I would imagine, is a slow process, unless the wood cells are somewhat porous. I'm not sure. Eventually the moisture probably escapes. What I was wondering is if the water escaping through the wood cells makes the cells relax a bit and releases tensions in the wood. Purely speculating here.

Share this post


Link to post
Share on other sites
1 hour ago, TedN said:

Well, if you felt grass clippings that were freshly cut and grass clippings that had been backing in the sun all summer, you'd be able to tell which one had moisture content and which one didn't, with a blind fold on. One is crisp and one is more malleable. I think you can do the same with wood, to some degree.

Fresh cut grass has a lot of free water, not just bound water.  Like cooked spaghetti vs dry.  If you had wood shavings, perhaps you might be able to tell 5% MC wood from 10% MC, but even that I think would be doubtful if it wasn't shavings from the exact same piece of wood.  I'd be even more doubtful you could tell much about the moisture content of a solid board, assuming the free water has been taken out.  Somewhere between might be a board with some surface fuzz, where you could perhaps detect some difference in the stiffness of the fuzz.

I handle wood quite often that has absolutely 0% (actually negative, if you go by standard methods) moisture content, and it is my perception that density is the most significant thing about the feel of the wood.  

One other thing is surface texture... according to the ideas I mentioned previously, a rough-sawn board should feel more dry than a smooth-planed one.

 

Share this post


Link to post
Share on other sites

Martin, I'm surprised to hear you say that you processed wood without end sealing. In my area any veneer or specialty log is immediately sealed at the time it is marked.

Ted, If you look up the structure of a tree you will see that the wood is made up of tube like cells and other structures whose purpose is to transport water up and down the tree. If the tubes are cut the water evaporates out of the ends much faster than it does through the sides of the wood and the difference in drying rates is what causes end checks. Sealing the ends slows (not stops) the rate of drying and evens out the difference. Wood cells are permeable to water and once the free water between the cells evaporates the bound water within the cells does evaporate over time. Too rapid drying can cause the cells to collapse which is undesirable but slow drying keeps the shape of the cells and leaves them hollow and empty of excess water.

Share this post


Link to post
Share on other sites
6 hours ago, nathan slobodkin said:

Martin, I'm surprised to hear you say that you processed wood without end sealing. In my area any veneer or specialty log is immediately sealed at the time it is marked.

 

In my neck of the woods this seems to be a practice confined to hobbyists.

The wood checks here anyway, and the area affected by end checks is about the first 3 cm which always gets cut off as soon as you dimension the timber, often simply because the cut isn't square or there's a bit of weather stain. 

I think veneer is a different matter - veneer logs usually sell for well over 10 times the cost per M3 of lumber, so the extra effort can be justified commercially.

A friend of mine who aran a bigger sawmill did a study showing that well over 50% of a felled tree is lost to processing before it becomes a piece of furniture - I don't suppose the proportion lost to end checks is more than about 2% of this.

Share this post


Link to post
Share on other sites

Martin, what species of wood are we talking about? In maple from this area (Northeast US) I would see much deeper checking. You are certainly correct that specialty logs are treated very differently than regular lumber as veneer logs are cut to exact lengths and there is little room for trimming. Most of the tone wood dealers in this area are  log buyers for veneer companys and can pull out likely tone wood from large numbers of veneer logs.

Share this post


Link to post
Share on other sites
On 1/13/2018 at 10:29 AM, nathan slobodkin said:

 A kiln is simply a tool for controlling drying conditions. While I think the cycling of wetter to drier conditions involved with air drying is beneficial for tone wood the correct use of a kiln to reduce surface moisture at the start of the drying process is often extremely valuable in reducing stain and preventing the start of fungal infection. As Martin said the overly rapid reduction of moisture content can lead to case hardening or checking including micro checking which while invisible is certainly not what we want in tone wood.

Regardless of how the moisture content was reduced there are other aging processes involving changes in resins and other factors which are very important in the processing of good tone wood and the kiln may shorten the drying time a bit but I don't use wood unless it;has been in my shop for years.

Agreed!

Wood has 2 kinds of water:  Free water and bound water.  Free water takes up space in the cell lumen or other voids.  Bound water is in the cell structure bonded with the cellulose. In general air drying will reduce or eliminate free water, but not effect bound water.  Kiln drying removes free water and a percentage of the bound water.  Loss of bound water relates to cell wall collapse and shrinkage. 

The issue is dimensional stability and predictability.  What is most important is to understand how your wood has been processed....as with most things: mysteries get in the way of progress.

on we go,

Joe

bound vs free water.jpg

Share this post


Link to post
Share on other sites
5 minutes ago, joerobson said:

Loss of bound water relates to cell wall collapse and shrinkage. 

The only times I have had cell walls collapse, it was in the process of removing the free water, and usually combined with elevated temperature.  Loss of bound water definitely does cause shrinkage, but as yet I have never had cell collapse from that.  Just my experience, not necessarily what happens to others.

On the topic of end checking, the reason for coating the ends is to slow down drying (and shrinkage) at the ends, which is the cause of the checking... but with the proper schedule of kiln drying and humidity, it seems like you could do the same thing to minimize the checking.  Air-drying, where it is more difficult to control the conditions, might need the end coating.

 

Share this post


Link to post
Share on other sites

Don is right. With a heat and vent kiln you are controlling moisture throughout the process and there shouldn't be much end checking unless you're caning it a bit.

With air-drying, it's not an issue in Scotland - the process is SLOW! There really is no such thing as a dry day ... north east US, very different story.

However, I still think that for general non-speciality wood, it's probably not commercially viable to coat the ends unless it has some sentimental value. All the split ends can go in a nice woodstove anyway.

I was mainly cutting oak, ash, sycamore, elm, lime ... principally oak. 

Share this post


Link to post
Share on other sites

Interesting thread.  I do not know anything about the world of violin wood, but in guitar making, air-drying is the benchmark for wood and kiln drying is suspect.  The thinking behind this is kiln drying rapidly accelerates the drying process and in doing so damages the wood at the cellular level.  Again, I know butkis about violin wood so I have no axe to grind here...

Share this post


Link to post
Share on other sites

When we measure the thickness of old instruments say at least 200 yrs old Cremonese vn, if it measures 3.0 now, does that mean it was thicker when it was new? If so , how much?

 

KYC

Share this post


Link to post
Share on other sites
32 minutes ago, chungviolins said:

When we measure the thickness of old instruments say at least 200 yrs old Cremonese vn, if it measures 3.0 now, does that mean it was thicker when it was new? If so , how much?

Going by torrefied wood as being the limit of the change, I'd say no more than 0.05 mm, or slightly over 1%.  

Using the same criteria, the width would shrink too, by about half the rate, or about 1.5 mm for a fiddle that started out 207 mm wide.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Recently Browsing   0 members

    No registered users viewing this page.