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Wood color.


Nick Allen

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6 hours ago, Don Noon said:

Nope.

Studies suggest that TM wood is prone to photobleaching under various light sources.  As a side note, studies also suggest that UV exposure will impact differently on earlywood vs latewood and sapwood vs heartwood.

It seems that lighting outside the UV range is also a player in wood colour change.  Understanding the different processes involved in the various frequency ranges, and they do seem to differ, may be helpful in providing a more complete understanding of aged wood appearance.

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4 hours ago, MikeC said:

Does torrefing / torrefaction?  what's the right word,  anyway does that involve heating in the absence of oxygen?   I thought that would partially carbonize the wood as in making charcoal but would not expect carbon to lighten under UV.  

No oxygen, but with steam.  Wood is made of several different materials, and each responds differently to heat and hydrolysis.  The temperatures are too low to cause cellulose to decompose significantly, but the other components undergo some amount of decomposition and re-polymerization.  I suspect the color comes from other things, not free carbon.  The full answer might be somewhere in the research papers somewhere.

54 minutes ago, John Harte said:

It seems that lighting outside the UV range is also a player in wood colour change.  Understanding the different processes involved in the various frequency ranges, and they do seem to differ, may be helpful in providing a more complete understanding of aged wood appearance.

Longer wavelengths, below UV and into the blue range, would penetrate deeper into the wood but have less immediate impact.  But with enough time, who knows what the effect would be.

To that end, here is the spruce test piece along with a weathered softwood (spruce, pine, fir) stick that was sitting outside for a few years, not in direct sun.  I have no idea what factor in the air/rain/light results in the coloration, but it's different... a kind of green/gray.  Some of the surface was planed off to get to intact wood, and the more you plane off, the more it looks like regular wood.2012290197_230129weatheredwood.jpg.85808989237444bc71ef276046bb680a.jpg

Of course, it would be totally impractical for a maker to leave unvarnished instruments around for years to develop the appropriate coloration, so some shortcuts or compromises would be necessary.

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2 hours ago, Don Noon said:

Longer wavelengths, below UV and into the blue range, would penetrate deeper into the wood but have less immediate impact.  But with enough time, who knows what the effect would be.

This paper may be of vague interest: https://link.springer.com/article/10.1007/s00226-013-0601-4   The conclusion provides a quick outline of the findings. 

 

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17 hours ago, Don Noon said:

Thanks, John.  As always, the skilled librarian to locate the appropriate paper.  Good stuff... looks like darkening followed by bleaching, to over-summarize it, and might explain why the white wood gets darker and the dark wood gets ligher.

Broadly speaking, this seems to be what ends up happening.  For more, see: https://www.researchgate.net/publication/280096685_Novel_color_stabilization_concepts_for_decorative_surfaces_of_native_dark_wood_and_thermally_modified_timber

While this particular study focuses on ways to mitigate photobleaching in dark woods (including spruce TMT), there is good material in the introduction that explains the various processes that occur in dark woods under UV and visible light.

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11 hours ago, Davide Sora said:

Thanks for sharing John, you are a real gold mine.:)

Thank you Davide.

Further to my above posts, there are a number of other studies that consider the ways in which various softwoods and hardwoods, untreated vs TM wood, earlywood vs latewood, sapwood vs heartwood respond to UV and visible light exposure.  If you are interested in any of this, let me know.

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18 hours ago, John Harte said:

Thank you Davide.

Further to my above posts, there are a number of other studies that consider the ways in which various softwoods and hardwoods, untreated vs TM wood, earlywood vs latewood, sapwood vs heartwood respond to UV and visible light exposure.  If you are interested in any of this, let me know.

I've read some articles on this topic, especially through the notifications on the Academia.org site, but I haven't found much specific to lutherie. If you have any papers to suggest it would be interesting, but I'm afraid the list might be too long, probably too much time for you to compile it and too much time for me to read it all.:)

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On 1/29/2023 at 8:36 AM, Davide Sora said:

Do you have any idea why the color lightens?

Photo degradation on already degraded or more degraded surface lignin as compared to un treated wood. All of it caused by UV exposure, this is particularly noticeable on Redwood as well as Walnut, both are often picked out by people because they love the original color, both notorious for greying/bleaching out. So much so that entire sub sections of coating industry has dedicated itself to creating products to thwart it.

In the past when people built redwood decks {stupid idea} they were sold to people who loved the original color, and many people were upset when they would start to turn grey and thus the exterior wood coatings industry came up with thousands of different products to counter this, all this does is create a lifetime of expensive maintenance that is not needed as the material exists just fine un-coated, same thing happens to Red Cedar shingles where people are constantly chasing a pipe dream of "red shingles" and thus spending insane amounts of money to "preserve" their shingles, where if they just let them turn grey, they last just as long as not being coated yet have the benefit of a uniform even color that needs no maintenance, most notable in Cape Cod style houses that use White Cedar shingles that are allowed to grey out and then often times having a verdigris green painted on all the trim, a much more sound approach to exterior wood.

Walnut, while not the most used material in homes is used and is notorious for turning, even with film building finishes on them, which is rather unique unto itself as most clear coated finish films prevent adverse greying/whiting out. It is highly recommended to stain walnut with a similar brown colored stain to preserve the color under clear coats lest it turn whitish anywhere sun hits it.

The thermal process damages the surface/internal lignin {not in a way that is detrimental to the over all board} and this already degraded material is more prone to UV bleaching and is also why it is more brittle

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3 hours ago, Don Noon said:

Sure is impressively bright.  It might be easier on the eyes if it was unplugged.

That is the finished product of this.  Also, it's presents different color in different lighting. This pictured, is the violin with just a ground coat on it.  I was responding to the ground coat question.

violin.jpeg

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4 hours ago, Davide Sora said:

I've read some articles on this topic, especially through the notifications on the Academia.org site, but I haven't found much specific to lutherie. If you have any papers to suggest it would be interesting, but I'm afraid the list might be too long, probably too much time for you to compile it and too much time for me to read it all.:)

There is a reasonable amount that could apply to lutherie, depending on what you want to make sense of.  For example, a study considering differences between early and latewood response to UV exposure might help someone make sense of the process that occurs with respect to darker annular rings in torrefied wood that Don has mentioned.  In a similar vein, someone may want to know more regarding the lighter sap strip that is seen in some old (and not so old) instruments.

Most of what I have found is not of much practical use.  If one wants to photoyellow instruments using UV lights, the most significant “finding” might be to avoid anything that emits light up into the visible blue range.  Mind you, it might be that some photobleaching following photoyellowing is actually beneficial...

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Richard4u  the first one looks too yellow for my tastes but I'm sure it would look good with a complementary colored varnish.   I had a PM from Manfio recently and his ground system is interesting.  I'll try it on some samples before my next build.  

Below is a sample with my current ground.  I'm preparing this so that I will have something to test my colored varnish before I put it on the violin. 

As for sun tanning I did not do it on my violin.  I don't think it really needs it.  However I do have a bowsaw made of curly maple that got some sun in a window and it gives a nice effect to the wood.  I don't understand the science of photo degradation of the wood.  I'm more into theoretical physics and cosmology but I like things that are blingy!   I have ADDOLS  attention deficit diso... oh look something shiney!  

 

 

 

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1 hour ago, MikeC said:

Actually I was going to comment that's a good ground but what varnish would he put on it?  It's too blond for my tastes.  Gentlemen don't always prefer blonds.  

You can dissolve gamboge into dewaxed clear shellac and brush it on if you want that yellow ground color.  You guys should use your imagination more.

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I don't want to use shellac though,  been there done that.   As for imagination how about a hybrid spirit oil varnish.  or a spirit varnish with an alkaline solution as the carrier or a spirit varnish with a turpentine carrier instead of alcohol.  The imagination runs wild.  

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2 hours ago, MikeC said:

Actually I was going to comment that's a good ground but what varnish would he put on it?  It's too blond for my tastes.  Gentlemen don't always prefer blonds.  

I can varnish this any color I want.  Just because my ground coat does not color the wood, they sky is the limit.

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