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Question for chemists: KOH as part of wood treatment?


Advocatus Diaboli
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I've experimented with this process as well. The results are lovely. I too have wondered about long term effects, but then I thought that this is basically the same process people have used to "set" the blacks of their purfling while dyeing. Wouldn't we know, through trail and error, any negative long term effects? 

I should add that my trial was with ferric sulphate (FESO4) not ferric nitrite; a minor,potentially major, difference. Also for those who are interested, there is some historical precedence with these chemicals. Known historically as "green vitriol" and "caustic potash" these materials have long been used as mordant dyes. You can see the VSA journal vol.14 no.3 "Information Sheet on Varnish and Ground" by Burritt Miller, and The Strad july 1987 "Salts of Wisdom" by Remy Gug. 

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Hi Mike (post 2), there is an advantage to rust in that it is stable. If anyone wants to have some fun, grind up a tablespoon of  ivory soap and melt in ca 1/2 cup warm water, add about a teaspoon of green vitriol  to 1/2 cup warm water, then, with very vigorous stirring, stream in the iron into the soap sol.  A waxy substance will  cling to various places, rinse til clear water, scrape on  coffee filter put on warm surface to dry. The stuff has an awful color, but when it is dry and you add to turp or varnish you have a beautiful violin red. You have made iron linoleate, iron and linseed oil chemically combined. This process was known in early times and was used to produce water proof cloth.

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David, I know you've had accelerated age testing done.  Do you know what process was used?

Most of it was high-intensity UV light, targeted toward color durability and varnish film changes, something along the lines of a few days exposure being equivalent to many years of normal exposure.

 

Some other changes can be accelerated with heat. What's the crude rule-of thumb? A 10 degree increase in temperature doubles the speed of chemical reactions?

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  • 2 years later...

This thread may well be dead, and I fully understand that chemical treatments can be a fool's errand... but I am curious on the process Mr. Diaboli and mdoddana are employing.  So you prepare a solution (in alcohol?) of KOH, and a separate solution of Ferric Nitrate, and allow time between these coats?   And is the aim for these to neutralize each other?

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AsaBB,   I'm curious about this also as it closely resembles a wood finish on a non violin related project I'm working on.   I think you may have it right that the solutions are applied separately. 

In my current application ferric nitrate is applied and heated to develop the color but if that could be done chemically without heating it would be much preferred. 

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Heating, UV exposure and alkali treatment would all give the same result - chemically. But colour is also dependent on things like particle sice and chmical bonding to the substrate, so the resulting colour might be different. In all cases the ferric ions will react with the wood, reducing that while itself getting oxidised to ferrous iron, forming (relatively) insoluble ferrous hydroxide. There are whole books written about that reaction, it was an important part of photographic processes once upon a time. Which really means that it is very complex and poorly understood, and potentially very useful.

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I have learned that ferric sulphate was used traditionally as a stain on 'harewood', an 18th century term for figured maple used in marquetry.  Still, it appears that in solution, ferric sulphate has a pH of about 1, while KOH is around 10.  This means they would not exactly end up neutral.   mdaddona, in your trials, did you also employ alternating applications of acid then alkali? 

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On 1/26/2016 at 1:55 PM, joerobson said:

One thing I have observed many times is that the reflective results of chemically treated woods are not the same as we see in untreated wood or old instruments.

This goes double for pigments or stains applied to the wood, in my observations.  Surface treatments I don't think look quite the same as a uniform color to the cell walls, which you'd generally have in untreated wood... new being lighter, and old being darker.  AD's iron oxide deposition process looks too burned to my eye.

I have tried nitrite and potassium dichromate years ago, and my violin #1, created with fresh wood and treated with those chemicals, I think looks pretty decent.  But the nitrite gives a gray color, and the dichromate a dark brown, so it needs some moderation and testing, and every piece of wood reacts a little differently.  I'd probably use nitrite and UV if I wanted to use fresh, white wood today... although I can't answer for any long-term effects.  My #1 is only  9 years old, but seems to have no ill effects.

On 1/27/2016 at 3:31 AM, David Burgess said:

...does anything come to mind which would darken the wood uniformly (not "burn" the end grain and summer growth on the top), not attack the wood much, and leave a residue which completely stops reacting with the wood? And also doesn't leave any hygroscopic "salt" residues?

Although this question was not directed at me, I can say yes to all of that, and most folks here know what it is. ;)

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I would advise against treating wood with strong base unless one is venturing into some serious experimentation. It could destroy the wood and ruin good instruments.  

Based on studies in our lab with infrared spectroscopy, strong base above pH 11 can cause hemicellulose hydrolysis in a day or two.

Controlling pH is very important. At pH 12, the hydrolysis is very severe in just one day. We are only soaking a small flake 1 cm x1 cm x 0.1 cm. How a thick board is affected by soaking is unpredictable. 

If one wishes to remove some resins and extractives with base, baking soda is a suitable choice. It is mild enough to not degrade the wood. But I am not sure if such washing is beneficial for tonewood.  

Search for "SEOH pH-Fix 7.0-14.0 Analytical Test Strips Box 100" on Amazon and one can get a rough pH reading (+/- 0.3 units). We use glass electrode pH meters in the lab for accurate detection. 

We have recently analyzed a Chinese guqin from 1500s and it has received base treatment. We received a small piece of wutong wood from repairs and its infrared spectra matches our samples soaked in pH 11.8 calcium hydroxide solution for 3 days. I do not know if this guqin sounds nice or not. What works for guqin may not work for violins. Wood treatment is a very tricky process. 

 

  

 

 

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4 hours ago, Bruce Tai said:

I would advise against treating wood with strong base unless one is venturing into some serious experimentation. It could destroy the wood and ruin good instruments.  

Based on studies in our lab with infrared spectroscopy, strong base above pH 11 can cause hemicellulose hydrolysis in a day or two.

Controlling pH is very important. At pH 12, the hydrolysis is very severe in just one day. We are only soaking a small flake 1 cm x1 cm x 0.1 cm. How a thick board is affected by soaking is unpredictable. 

If one wishes to remove some resins and extractives with base, baking soda is a suitable choice. It is mild enough to not degrade the wood. But I am not sure if such washing is beneficial for tonewood.  

Search for "SEOH pH-Fix 7.0-14.0 Analytical Test Strips Box 100" on Amazon and one can get a rough pH reading (+/- 0.3 units). We use glass electrode pH meters in the lab for accurate detection. 

We have recently analyzed a Chinese guqin from 1500s and it has received base treatment. We received a small piece of wutong wood from repairs and its infrared spectra matches our samples soaked in pH 11.8 calcium hydroxide solution for 3 days. I do not know if this guqin sounds nice or not. What works for guqin may not work for violins. Wood treatment is a very tricky process.

Hi Bruce,

thanks for the valuable information.

I would like to ask, do the pH indicator litmus papers work the same way for gases like ammonia?

I know some use some gaseous substances to oxidize the wood and I was wondering if the reading of the pH of vapors with the litmus paper would be reliable.
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12 hours ago, Don Noon said:
On 27. 1. 2016 at 12:31 PM, David Burgess said:

...does anything come to mind which would darken the wood uniformly (not "burn" the end grain and summer growth on the top), not attack the wood much, and leave a residue which completely stops reacting with the wood? And also doesn't leave any hygroscopic "salt" residues?

Although this question was not directed at me, I can say yes to all of that, and most folks here know what it is. ;)

I guess it's called "time and UV". If there's something else please let me know as well.

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1 hour ago, HoGo said:

I guess it's called "time and UV". If there's something else please let me know as well.

Don may be referring to his carbonation method?  It's the same way charcoal is made.  Heating wood in the absence of oxygen.  But old wood can look very white where it's been protected by coatings.  

 

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Isn't he cooking the wood wet? Charcoal is not made in complete absence of oxygen. Torrefaction is the process where Nitrogen is substitued fro atmosphere. I've succesfully torrefied wood in kitchen oven without nitrogen atmosphere, I dried it to 0% MC and packed tightly in thick aluminum foil and sealed with heat proof aluminum tape. Then baked.

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2 hours ago, MikeC said:

Don may be referring to his carbonation method?  It's the same way charcoal is made.  Heating wood in the absence of oxygen.  But old wood can look very white where it's been protected by coatings.  

"Torrefied" has more variables than "cooking".  Time, temperature, atmosphere, pressure, and various sequences of various combinations, all with possibly different outcomes.  The general idea is to remove a small amount of hemicellulose/lignin, and polymerize what's left to become less hygroscopic, with a side-effect of becoming darker.  There is some reason to believe that this process happens naturally at a very slow rate.

My observation of old wood in violins is that it is extremely dark and opaque.  It's not so apparent until you do comparisons under identical lighting conditions.  This is a photo of a 1714 Strad and one of mine with torrefied wood.  My torrefied wood in this particular instrument was one of the more lightly processed examples, but the difference is obvious.  

5aa29ec396f3c_Maple-processedvs1714.jpg.4c03d87792e36a3fe0b394832f5235e5.jpg

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If we are speaking of wood color...and not other factors....

The Brandmair research confirms the observation that the wood protected by varnish is a lighter color than the wood in worn areas.  The degree of color change being a function of the degree of wear.

There are other ways to control wood color without the predictable or unpredictable application of oxidizing agents or concentrated UV treatments.

Joe

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