The dangers of wood treatment

[Bruce Tai]

The other day I was talking to a restorer in Taiwan who said that when he was studying violin making in Cremona, he heard that a maker were treating carved tops with electric arc (plasma discharge). It was said to be a way of artificial aging. Then many years later he saw a couple instruments by that maker cracking so badly in a manner that he never thought would be possible. This reminds me how dangerous wood treatment is.

 

[Edit: from the discussion below I realize this is a corona discharge device which will generate ozone and nitric dioxide.]

 

There are always some fanciful ideas about how Stradivari may have applied special wood treatment or used specially treated wood. Such ideas have definitely attracted many good makers to experiment with various wood treatments. Rumor has it that Vulluame tried many kinds of chemical treatment and baking, but in the end those treated wood did not age well and good instruments became wasted (are these stories real?). More recently we have Sacconi proposing potassium silicate as a hardener, but its basicity would cause the exact opposite effect, the disintegration of wood through hemicellulose degradation.  

When I think about so many possible treatment methods of tonewood, such as acidic solutions (pH<3), basic solutions (pH>10), heating, steaming, boiling, fuming with ammonia, baking. They have one thing in common, which is to cause the hydrolysis of hemicellulose. Of course individual results would vary case-by-case, but I imagine that the initial impact of these treatments on acoustics may be benign or even beneficial. Some believe that reducing hemicellulose content will reduce hygroscopicity of wood and reduce damping. But it does not stop here. Several papers I read suggest that about 5% of hemicellulose will be hydrolyzed per year just due to normal aging indoors under good storage. But hemicellulose is naturally crosslinked to hemicellulose (not to cellulose) at the frequency of 70 linkages per 1000 aromatic rings. So after 300 years of just natural aging, a quarter of such linkages may be lost, and the ligin network is weakened. Lignin acts as the cement in wood cell walls and fibers. So hydrolyzing hemicellulose has far reaching consequences which are still not clearly understood. 

 

On the other hand, UV, exposure to the sun, and plasma discharge will probably affect lignin more, causing oxidation (yellowing) and degradation. I am amazed to read papers on how much lignin can degrade at the surface after just one day exposure under direct sun light. Lignin degradation is probably even more damaging to wood stability than hemicellulose degradation. 

 

[Edit: the corona discharge will actually generate ozone to oxidize lignin, and generate nitric dixoide which will create nitric acid and nitrous acid upon contact with moisture and cause hemicellulose hydrolysis. Very drastic indeed.]

 

Biological attacks depend on which fungi or bacteria are in action. Some mainly attack holocellulose, while others attack lignin and holocellulose--there are many varieties. Again, wood becomes more degraded, not more bonded.

 

Some people may point to Nagyvary's Nature paper in 2006 and say that the wood in the Strad and del Gesu violin has a lot of degradation in hemicellulose and lignin. I always had my doubt because I "imagined" that wood would be stronger in Stradivari instruments to produce those beautiful high notes. Nagyvary said maybe lignin was more modified than degraded, which could also explain the NMR spectra. He is very kind to give me the leftover samples for re-analysis. While we are not ready to publish our full finding yet, the Strad and del Gesu violin maple only showed minor degradation in NMR, in a manner consistent with natural aging under good storage. How could we see different spectra in the same sample? While some of you will think it is due to sampling different spots, the actual reason is due to setting proper instrument parameters. We have much more powerful NMR instrument these days to be able to search for the best parameters and scan under multiple conditions, due to shorter scan time. Nagyvary also showed a Strad cello with only minor hemicellulose degradation, which he thought could be caused by natural aging, and we got a very similar spectra as he did on this cello, and the 13C spectra of this cello is very similar to that of the Strad and del Gesu violin. To cut a long story short, all three instruments showed minor degradation of hemicellulose which may be consistent with natural aging. Now if anyone can send me maple samples aged naturally for over 200 years, we could use it as a really good control for comparisons. We just have better instruments than 10 years ago, and hence we could measure better spectra that represent the wood more accurately. 

 

Our study will be published when it's completed (no secrets), but as of now I have failed to find evidence to suggest that Stradivari's maple was degraded artificially, and we have two more pieces of his maple from 2 different sources to provide more clues. The change we saw with lignin is complicated and needs to be more carefully researched. Again, some aged maple will help us interpret the NMR spectra better. 

 

Based on our latest finding, I of course do not agree with the idea that microbial degradation is good for tonewood. From what I have read, fungus is the enemy of valuable wood. I doubt if we will see the sign of fungal degradation of wood fibers in any sample. As I said, two more Strad maple samples are waiting to be analyzed by NMR. One came from an European restorer and one from an Asian collector. At this point it is too early to talk about wood reinforcement at the molecular level, although we are looking into this. Nagyvary has proposed borax as a crosslinker of wood fibers, but it's not that simple. First you have to know if the boron he found were just borax minerals stuck in the empty cell lumen or if it went into the cell wall structure to bind wood fibers. If it is binding, how is it binding and what is it binding to? These are super challenging issues in chemical analysis. Let us not jump to the conclusion that Stradivari used borax for wood hardening yet, but we are looking very deeply into this with state-of-the-art instruments.  

 

Before people get too excited about secrets of wood treatment, I would like to bring up the dangers of wood treatment. The degradation of hemicellulose and lignin will most likely affect the durability of instruments 50 years down the road. I would really hate to see many new beautiful instruments become badly degrade in 50-100 years because of misguided wood treatments. So perhaps it would be good to bring this issue to the open, and the horror story I heard with electric arcs is probably not a singular event. Can we openly discuss this issue and let people know that certain practices will very likely ruin the wood over the long run? More horror stories about improper wood treatment? 

[~ Ben Conover]

Hard to say what things will look like in 50 years, but using traditional ingredients to treat / preserve wood seems logical.
Otherwise you may as well use Cuprinol woodworm preservative. 

Myrrh smells nice and protects the inside of instruments from big humidity changes. 

[Benthoven]

Fascinating subject, and I'll be looking forward to the results of the research. 

 

StewMac has started supplying "torrefied" tonewood for guitars that "looks and sounds like wood that's been broken in for many years."  Have you sampled any of this product?  The process involves heat-treating in an oxygen-free kiln, but it's not clear if there is any chemical process involved.  I've just ordered a piece of torrefied spruce "uncarved guitar brace" material for $9, a piece of quarter-sawn 20" x 2" x 3/4" spruce stock, to make my fills for top cracks with spruce that already has the patina and dimensional stability of aged wood.  They also supply torrefied maple neck blanks for guitars, etc., but I would presume they will make violin sets available at some point as well.  I'd be very curious to see your research include some torrefied woods for comparison to these other processes.

[Don Noon]

Bruce,

 

Here are a couple of previous threads on various processes and problems:

http://www.maestronet.com/forum/index.php?/topic/321592-ozone-treatment-prior-to-ground/?hl=%2Barc+%2Bozone+%2Bnitric#entry464407

http://www.maestronet.com/forum/index.php?/topic/225405-ozone-again-and-other-methods-of-self-sabotage/?hl=%2Barc+%2Bozone+%2Bnitric#entry225406

http://www.maestronet.com/forum/index.php?/topic/328152-wood-mistreatment/?hl=%2Barc+%2Bozone+%2Bnitric#entry581631

http://www.maestronet.com/forum/index.php?/topic/320196-violins-from-thermally-modified-wood/?hl=+arc%20+ozone%20+nitric

http://www.maestronet.com/forum/index.php?/topic/331414-with-all-the-whacky-ideas-weve-had-about-wood-treatments-lately/

http://www.maestronet.com/forum/index.php?/topic/326803-violin-fungus/?hl=%2Bfungal+%2Btreatment#entry556042

 

There are certainly infinite variations that can be tried to modify wood, and even infinite variations in each subset.  For example, "baking" variables can be temperature, time, pressure, atmospheric composition, and then you can have sequences of those variables, just to multiply things geometrically.

 

From an engineering perspective, there is no reason to think that spruce trees have created the perfect acoustical material for us, even with whatever amount of natural aging.  For example the tree might have its own reason to put in more hemicellulose than we'd need for a violin top.  I do appreciate the amazing properties of spruce, and it is a wonderful soundboard material... but is it the "best"?

 

I'll try not to make this a blatant pitch for hydrothermal processing, but it's what I know best, so I'll just talk about that.  There are good reasons (some of which are mentioned by Bruce, or covered in the referenced threads) why I'm not using the other things like ozone, ammonia, silicates, and fungus.

 

I have no doubt whatsoever that careful hydrothermal processing can increase speed of sound, decrease density, and decrease damping in spruce... all of which would appear to be good from an acoustics standpoint.  There is good reason to believe that many of the chemical processes of this treatment are similar to long-term natural aging, with some likely similar results in the mechanical/acoustic properties.  Some secondary features also appear to match up:  more brittle, darker, opaque, shrinkage. 

 

The biggest danger many processes is leaving some detrimental products in the wood that cause unwanted deterioration.  Natural aging breaks down hemicellulose, but most people don't seem to worry about the acids that are the byproduct of that breakdown, as if natural processes must be the best.  But perhaps some mild alkaline material (borax?) would provide some beneficial protection.  That's just speculation, though.  For hydrothermal processing, I believe there are ways to manage the process to remove the acidic byproducts fairly well, with little worry about post-processing degradation.

 

For anything, the bottom line is a trade-off of properties.  With hydrothermally processed wood, you can get higher theoretical acoustic performance at the expense of easier splitting, but reduced likelihood of shrinkage splitting.  I think that may be the same with old violins.  

 

If you look at the total lifetime of a violin, sure, removing some of the non-cellulose material is likely to shorten the lifespan.  That's what "artificial aging" is supposed to do, with the idea that you get the character of a 300 year old instrument without having to wait around 300 years for it to mature.  What is the expected lifetime (starting now) of a 300 year old Strad?  Nobody can say for sure.  Likewise, nobody can be sure how long a violin made from hydrothermally processed wood will last... but there is decent rationale to think it should live a very long time.  The oldest one I have is just under 6 years old, with no apparent degradation.

 

OK, I guess that does sound like a pitch, doesn't it?

[Wm. Johnston]

Have you considered having a small sample of your processed wood analyzed (with NMR?) to see if the thermal processing is really equivalent to 300 years of natural aging? Seems like it would be able to show if the same chemical changes happened but it wouldn't say anything about the physical properties, but you've measured many of those already.

[David Burgess]

Thanks, Bruce. Looking forward to what you find. And thanks for the warning too.

"Ozone treatment" (is that the "plasma discharge" thing?) was pretty popular for a while, but I don't hear much about it being used any more

[Michael_Molnar]

To put all wood treatment into the same basket is wrong. I can say from my own experience that ammonia treatment can degrade the wood long term. Also, I have seen evidence that anything involving nitric acid or anything similar will also set up a long lasting degradation process. I have heated wood and sometimes got nice results. However, it was never consistent, so I stopped.

 

The big issue with wood treatment is that everyone's process is probably different, making comparisons and evaluations difficult. Nevertheless, there are some that we should avoid.

 

BTW, I want to hear from ammonia treatment users. What do you find?

[Marty Kasprzyk]

Has anybody ever used gamma ray treatment for violin wood? It occurs naturally and it may be responsible for some long term property changes.

 

Museums use it in high dosages for wood preservation and the old museums I've visited look in pretty good shape.

[yancypup]

Marty, I believe with gamma ray treatment you run the risk of the violin turning green and morphing into a bass from time to time (when it is pissed).

[Don Noon]

Gamma radiation is used to preserve food by killing off live stuff that might spoil it, so I would presume museums would use it for the same purposes... killing bacteria and other buggers.  There is some degradation of the base food, and likely whateveritis that the museums might be zapping, but presumably that is an acceptably minimal consequence for killing the bugs.  I don't see that it would be very useful for improving wood properties, just perhaps preserving it if things are eating away at it.

[Bruce Tai]

I think David Burgess is right, the electric arc is probably for generating ozone. Some of the older posts shared by Don Noon mentions UV generation as well in the ozone box. Sorry for not being familiar with this particular treatment. Without going into the papers for detail, ozone is such a strong oxidizing agent that lignin will get oxidized, and modified in complex ways quickly. Cellulose and hemicellulose will get modified, too. I need to check into the literature to see how much depolymerization there is for each of the biopolymer. Ozone is very small and will diffuse very quickly into very deep spaces in the cell wall.

 

Each treatment can be applied to different degrees or in combination. So it's very complex. But it is also interesting to think about shared trends.

 

While analytical methods like NMR and infrared or Raman spectroscopy can tell the overall features of organic composition. It cannot tell which molecule is modified where at the micrometer level (cell wall layers) and at the ultrastructural level (polymer network configuration). Even if a piece wood treated by hydrothermal or dry heating appears to have similar spectra, there is no way to tell if the microscopic changes are similar or not. Bulk measurements like elasticity or speed of sound may provide secondary clues. We must concede that wood analysis is a very difficult thing for modern chemistry and our scientific understanding is still weak. 

 

I think Gamma radiation is a good way to immediately stop existing biological attacks, not future ones. You only need to create some breaks in DNA to kill a microorganism. Although wood fibers will be damaged a little bit but probably negligibly so.   

[pbelin]

About ozone treatment, I think in our case it's more NO2 than ozone. (which is not any better)

I did try it, and without humidity the effect isn't very visible.

Can someone elaborate on the effect of ammonia (fumes or directly brushed on)?

I heard so many stories about how bad ozone and nitric acid are but have never seen the negative effects myself. (fading purfling, glue joints breaking, wood crumbling away and so on...) I'd like to see a picture of that...

[~ Ben Conover]

Lots of makers don't do anything at all about 'treating' the wood. 
 

[Craig Tucker]

Lots of makers don't do anything at all about 'treating' the wood. 

 

 

Except for perhaps - natural aging in stacked billets - and waxing or coating the ends .... ?

I always also wonder why the push towards artificial aging, or somehow 'treating" the billets of wood also.

Though this is probably the wrong thread to consider such a radical wood treatment.

I'm thinking that you're most probably correct - lots of makers don't do anything at all about "treating" the wood.

 

And probably, it's simply a 'philosophical' difference of opinion about, what 'works', what doesn't, and why it works the way it does.

[Marty Kasprzyk]

I think David Burgess is right, the electric arc is probably for generating ozone. Some of the older posts shared by Don Noon mentions UV generation as well in the ozone box. Sorry for not being familiar with this particular treatment. Without going into the papers for detail, ozone is such a strong oxidizing agent that lignin will get oxidized, and modified in complex ways quickly. Cellulose and hemicellulose will get modified, too. I need to check into the literature to see how much depolymerization there is for each of the biopolymer. Ozone is very small and will diffuse very quickly into very deep spaces in the cell wall.

 

Each treatment can be applied to different degrees or in combination. So it's very complex. But it is also interesting to think about shared trends.

 

While analytical methods like NMR and infrared or Raman spectroscopy can tell the overall features of organic composition. It cannot tell which molecule is modified where at the micrometer level (cell wall layers) and at the ultrastructural level (polymer network configuration). Even if a piece wood treated by hydrothermal or dry heating appears to have similar spectra, there is no way to tell if the microscopic changes are similar or not. Bulk measurements like elasticity or speed of sound may provide secondary clues. We must concede that wood analysis is a very difficult thing for modern chemistry and our scientific understanding is still weak. 

 

I think Gamma radiation is a good way to immediately stop existing biological attacks, not future ones. You only need to create some breaks in DNA to kill a microorganism. Although wood fibers will be damaged a little bit but probably negligibly so.   

Some people speculate that the thousands of year old wood found in Egyptian tombs is still in good shape because of the massive stone constructions shield the wood from being exposed to natural gamma ray radiation.

 

Gamma ray (shorter electromagnetic wave length than UV) radiation degrades the wood's elastic modulus in proportion to the dosage.  Low level natural gamma radiation over hundreds of years may cause a significant amount of damage if the wood is unshielded.

 

 

So if old wood is supposedly better than new wood it may follow that a high elastic modulus or speed of sound isn't desirable in the first place.

[Michael_Molnar]

Lots of makers don't do anything at all about 'treating' the wood. 

 

Right. I got suckered into this when I was new to making. I thought it would be a shortcut to getting a nice violin. I was wrong. I wasted a lot of wood and time. Nevertheless, I do encourage research in this area that could help us understand sound production.

[Bill Yacey]

From a historical standpoint, how could they possibly have generated ozone in the 18th century?

[Bill Yacey]

Some people speculate that the thousands of year old wood found in Egyptian tombs is still in good shape because of the massive stone constructions shield the wood from being exposed to natural gamma ray radiation.

 

I think more likely this wood is so well preserved due to the low humidity of the desert. No humidity, no micro-organisms.

[DarylG]

There is a short chapter in William Fulton's book titled "Sun-Browning the Violin" about the so called ozone treatment. It also mentions that it was presented as a talk at the 1987 Convention of the Arizona Association of Violin Makers. I don't know if this is the origin of this treatment or not. I had heard the horror stories before I got the book and never tried it myself. 

[Don Noon]

Lots of makers don't do anything at all about 'treating' the wood. 

 

It sure is less hassle, and usually easier to work  I have made 3 of them that way, and the results seemed to be fine... but there just seems to be little more zing to the processed wood.  If I didn't hear something different, I would go through the considerable effort to process the wood.  But the natural variability of wood is much greater, so pre-selection is critical, processing secondary.

 

In theory, the measured "improvements" would hardly be noticeable, if at all (although it's hard to say what difference damping would make, and that's the largest change in properties).

 

So if old wood is supposedly better than new wood it may follow that a high elastic modulus or speed of sound isn't desirable in the first place.

 

Then I suppose we shouldn't use spruce, since it has a high modulus and speed of sound?  Lead, maybe? 

 

The chart shown in another topic indicates that old wood DOES have higher modulus and speed of sound (http://www.maestronet.com/forum/index.php?/topic/331528-300-year-old-spruce/?p=691429).

Also, from the measurable signature modes of old violins, one can conclude that the old wood isn't particularly floppy.  My "copy" of the ex-Jackson came out slightly lower on signature modes, and I recall George Stoppani mentioning that his copy of the Titian also was lower frequencies than the original.

 

I think it would be more accurate to say that exceptionally high modulus or speed of sound is not necessary for a great sounding violin, but it doesn't hurt, and might help a little.

[Bruce Tai]

About ozone treatment, I think in our case it's more NO2 than ozone. (which is not any better)

I did try it, and without humidity the effect isn't very visible.

Can someone elaborate on the effect of ammonia (fumes or directly brushed on)?

I heard so many stories about how bad ozone and nitric acid are but have never seen the negative effects myself. (fading purfling, glue joints breaking, wood crumbling away and so on...) I'd like to see a picture of that...

 

I am not sure if so-called ozone chambers are using corona discharge.

It is well known that corona discharge can generate nitric oxide NO, nitric dioxide NO₂, and ozone O₃:

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

 

Nitric dioxide, when dissolved into water, generates nitrica acid HNO₃ and nitrous acid HNO₂. This is going to cause hemicellulose hydrolysis. 

So many treatments all lead to hemicellulose degradation. But this is not to say that they are more or less equivalent. At the molecular level, which sites get degraded and the side reactions can vary. We cannot pretend to really know what is going on. 

 

Does anyone have a picture of the so-called ozone chamber used to treat wood showing the arc lamp inside?

[David Burgess]

 

Does anyone have a picture of the so-called ozone chamber used to treat wood showing the arc lamp inside?

I think most were using a high voltage transformer, like that from a neon sign, to jump an air gap between two electrodes inside an airtight container. That's about all I know about it.

[Bruce Tai]

I think most were using a high voltage transformer, like that from a neon sign, to jump an air gap between two electrodes inside an airtight container. That's about all I know about it.

 

That sounds like a simple corona discharge device. O₃, NO and NO₂ are toxic, so I guess care must be taken when operating these things. It is almost unimaginable to me that anyone would allow NO₂ to diffuse into their wood. This thing should be banned in all violin workshops. 

[Piergiuseppe]

 

 

something you can see here:

 

 

 

https://www.google.it/search?q=wimshurst&tbm=isch&tbo=u&source=univ&sa=X&ved=0CDEQsARqFQoTCI_tot6bx8cCFcvAFAodMNIIkA&biw=1205&bih=608

[pbelin]

That sounds like a simple corona discharge device. O₃, NO and NO₂ are toxic, so I guess care must be taken when operating these things. It is almost unimaginable to me that anyone would allow NO₂ to diffuse into their wood. This thing should be banned in all violin workshops.

Believe me, it's been done.. . Its how we fumed boxwood in Newark. A bit of dilute nitric acid, a copper coin in it and there you go. When you grow older you learn how toxic that is.

It gives a very nice color to the wood (yes, I tried on a violin, no, it's never been sold, or even strung up) but somehow quickly turns to a muddy brown.