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The dangers of wood treatment


Bruce Tai
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In 1985 I saw (and made) quite a few instruments treated with the nitric acid and a penny treatment. Short exposures resulted in a very nice brown color on the wood and I have heard from musicians who are happily playing on them today.  Longer exposures resulted in cracking of the tops sometimes within just a year or two. I described this process to a chemist who told me we were lucky not to have developed serious lung problems from even trace exposure to this gas. I now content myself with UV light and a  very dilute, mild oxidizing agent .over a sealer to prevent penetration into the wood.

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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.

 

Why copper coin? What does it do? 

Was the coin immersed in nitric acid? 

I guess it is one of these reactions:

Cu(s) + NO3- + 2 H+ = Cu+ + H2O + NO2 (g) 

2 Cu(s) + 2 NO3- + 4 H+ = Cu2+ + 2 H2O + 2 NO2 (g)

As copper is oxidized by nitric acid, nitric acid is reduced to NO2

A very clever reaction indeed, but the result is again another way to degrade hemicellulose to make the wood fragile. 

NO2 can dissolve in water and generate nitric acid and nitrous acid, and the nitric acid oxidizes lignin to become yellow color. 

Very cool chemistry, but the principles of chemistry would suggest a destructive influence on wood. 

 

So I assume that quite a few makers makers would like to have the wood yellowed. Is it because it looks better under the varnish. Or is it a way of antiquing? Or is it just awesome to look at before varnishing? 

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The blazing whiteness of fresh wood is difficult to get to look like anything other than blazing white, even under colored varnish.  Something needs to be done to darken the wood to tone it down before the varnish goes on.  There's more in this thread: http://www.maestronet.com/forum/index.php?/topic/328896-seeing-into-wood-how-far-really/

 

Something I failed to mention earler:  the vast majority of hydrothermally processed wood is produced for construction purposes, primarily as a more dimensionally stable, biodegradation-resistant material.  A lot of development has gone into this, so I doubt it is going to be prone to rapid deterioration.  Yes, there are known reductions in ultimate strength and split resistance, but that doesn't mean it will be prone to distortion or shrinkage cracks too.

There's a ton of information in the "Thermowood Handbook" here: http://files.kotisivukone.com/en.thermowood.kotisivukone.com/tiedostot/tw_handbook_080813.pdf

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Thanks Don, the idea of noting seeing to fat to enhance the illusion of depth is a novel and interesting idea for me. 

 

For some wood types, boiling for a short period seems to help with drying and dimensional stability. This is the genral impression I have from reading about some wood crafts.  To what extent wood is modified depends on how it is actually applied. But I think boiling or steaming, or nowadays some kind of autoclaving, may make wood more stable for certain applications with little change in strength if applied in moderation. If applied in excess, the mechanical strength of wood is going to be compromised.  

 

Don Noon, do you apply hydrothermal treatment to green wood or after they have been air dried for years? Or some stage in between?    

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The blazing whiteness of fresh wood is difficult to get to look like anything other than blazing white, even under colored varnish. Something needs to be done to darken the wood to tone it down before the varnish goes on. There's more in this thread: http://www.maestronet.com/forum/index.php?/topic/328896-seeing-into-wood-how-far-really/

White wood is really a problem under the varnish, it just doesn't look good.

And any kind of stain also looks wrong, as it doesn't color the wood evenly.

Some old violins seem to have a very light ground (a Rogeri we had recently here comes to mind), but if you compare directly with different shades of wood you notice that it isn't so white...

Another thing: you can make a dark instrument with dark varnish on a light ground, but when the many 1000s watts of light hit them in the concert hall these instruments often look like fire extinguishers.

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Don Noon, do you apply hydrothermal treatment to green wood or after they have been air dried for years? Or some stage in between?    

 

Just because most of my wood is fairly fresh, most of the treating I have done has been on fairly fresh wood (but not green, damp wood).  The oldest has been ~5 years old thus far, for spruce.  I have done some maple a bit older.

 

I have experimented with boiling... at best, there seems to be a slight gain in properties.. At worst, there's cell collapse, severe warping, and splitting.  Other processes are better.

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White wood is really a problem under the varnish, it just doesn't look good.

And any kind of stain also looks wrong, as it doesn't color the wood evenly.

Another thing: you can make a dark instrument with dark varnish on a light ground, but when the many 1000s watts of light hit them in the concert hall these instruments often look like fire extinguishers.

I always use pre-stain conditioner on all to be varnished pieces.  I believe it's a Min-wax product.  I let it dry completely before I apply 2 shades of alcohol stain.  After they are dry I rub them out with a Windex/ammonia soaked rag or just ammonia and a rag.  It gives an even shade of tanning or golden depending on how a person sees things.  Good enough for me.

 

I haven't tried the 1000's watts of light yet, I would like to see my work under lights, I think. 

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Bruce,

 

I have used potassium nitrite on the wood. Is that going to destroy the wood?

 

Thanks

 

John

 

Potassium nitrite once dissolved in water will form a weak oxidizing agent and be slightly basic. So it is not highly destructive. That's about all we can say judging from basic scientific theories. 

 

The actual effects need to be carefully studied and is highly dependent on the exact situation. This is the gap between scientific considerations and actual practice. I have no practical experience on such matters. 

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Borax has a few other useful qualities apart from it's potential structural possibilites. 

Borax repels and kills insects.  Borax is one of the best all purpose fungicides and it can help reduce oxidation.  Borax can also act as a buffer to stabalize ph.

Even if it does not strengthen the structure it is quite likely that it helps reduce the weakening of structure over time.

 

In doping cones for making speakers, some borax compounds have been strongly advised as being effective at maximizing the transfer of energy from the cone to the air.  Some of the physics seemed to make sense at the time, but audiophiles have been know to delude themseves from time to time and without a bit more rigor in the experiments I am not sure how much faith to put in this.

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In doping cones for making speakers, some borax compounds have been strongly advised as being effective at maximizing the transfer of energy from the cone to the air.  Some of the physics seemed to make sense at the time, but audiophiles have been know to delude themseves from time to time and without a bit more rigor in the experiments I am not sure how much faith to put in this.

 

"Have been known to delude themselves from time to time"?

Much like (us or we) violin makers tend to do upon occasion, I would imagine. 

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In doping cones for making speakers, some borax compounds have been strongly advised as being effective at maximizing the transfer of energy from the cone to the air.  Some of the physics seemed to make sense at the time, but audiophiles have been know to delude themseves from time to time and without a bit more rigor in the experiments I am not sure how much faith to put in this.

 

I have never heard of doping borax to paper (?) cones to make speakers work better? Any link or reference? 

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I have never heard of doping borax to paper (?) cones to make speakers work better? Any link or reference? 

I seriously wish I could find links and references.  Sadly the last time I worked with making speakers, I was using a dial up modem to log onto a bulletin board to exchange information.  So my information on diaphragm impregnation and doping is from fairly ancient memory.  Boron does however have quite a bit of verifiable modern use acoustically.  Boron Carbide has a decent enough vibration propagation velocity.

 

http://techon.nikkeibp.co.jp/english/NEWS_EN/20141211/393943/

 

http://www.pearl-hifi.com/06_Lit_Archive/07_Misc_Downloads/Cone_Diaphragm_Mtls.pdf

 

In the book, "High Performance Loudspeakers, by Martin Colloms, the characteristics of boron listed are pretty amazing.   Density 2.4 Youngs Modulus 39 Specific Modulus 16.5 Sonic Velocity 12.7.

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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. 

 

Potassium nitrite once dissolved in water will form a weak oxidizing agent and be slightly basic. So it is not highly destructive. 

 

Bruce,

Do you think potassium nitrite could be safer for darkening the wood than UV exposure? I've been tanning my violins for several weeks in the lightbox as an alternative to using chemical treatments with the notion that this would be less damaging to the wood. Am I wrong?

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Bruce,

Do you think potassium nitrite could be safer for darkening the wood than UV exposure? I've been tanning my violins for several weeks in the lightbox as an alternative to using chemical treatments with the notion that this would be less damaging to the wood. Am I wrong?

 

Sorry, I do not work with wood at all. I only look at things from the theoretical side. The combined heat (infrared), visible light, and UV from the sun could measurably damage lignin fibers at the surface in just one day. How that translates to a specific UV box I am not sure. Lignin is affected by UV much more than carbohydrates.

 

For all I know, natural air-dried tonewood from trusted suppliers has been a highly consistent material for building great sounding violins. Fanciful and unproven methods of wood treatment could lead to poor sounding instruments with deteriorating wood in a few decades. If a hand-built master violin does not serve humanity for at least 100 years, it would be a shame.

 

I am afraid that if some future research again indicates that Stradivari's wood shows some signs of artificial manipulation, there will be a fad to experiment with even crazier combinations of wood treatment which will ruin many well-built violins. And yet we must be aware that wood is a very complex material and it is hard to see the chemistry inside. Every time we do an experiment and collect partial information, we may formulate a different theory about the status quo of his wood after 300 years and how to mimic it. This could lead many people to chase after the wrong wild goose and waste serious efforts. 

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Also worth mentioning is an article by Koen Padding (J. Violin Soc. Am. VSA Papers Summer 2007,Vol. XXI, No. 1), where he notes he isn't a fan of UV tanning to darken wood.

 

Here is a quote 

 

"This writer is not a great fan of coloring wood by means of UV, neither natural nor artificial. Although I do not want to suggest that mild natural (or artificial) sun tanning will already cause objectionable damage; wood that has gone brown by being in the sun for a long time loses some of its elasticity and ultimately becomes quite brittle, to the point of being unusable. To me this demonstrates that tanning is in principle a destructive method that should be practiced with caution."

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Also worth mentioning is an article by Koen Padding (J. Violin Soc. Am. VSA Papers Summer 2007,Vol. XXI, No. 1), where he notes he isn't a fan of UV tanning to darken wood.

 

Here is a quote 

 

"This writer is not a great fan of coloring wood by means of UV, neither natural nor artificial. Although I do not want to suggest that mild natural (or artificial) sun tanning will already cause objectionable damage; wood that has gone brown by being in the sun for a long time loses some of its elasticity and ultimately becomes quite brittle, to the point of being unusable. To me this demonstrates that tanning is in principle a destructive method that should be practiced with caution."

 

This is interesting and I have great respect for Koen Padding's work but I can't help but wonder if UV is really any worse than the chemical wood coloring treatments he sold? My experience has been that tanning, as well as the Magister primers, is only a surface effect and you can scrape it off pretty easily. Has anyone done any measured testing of the effects of UV tanning?

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