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Grain variation and properties variation


Don Noon
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There was a discussion that covered some of this ground a few years ago here, but I thought I'd just start a new one.

I have had a Sitka board for 40 years or so that shows some extreme differences in grain, and corresponding variations in properties when strips were cut in the different grain zones.  I had occasion to cut some more strips, and again saw some extreme differences:  from .37g/cc, 5800m/s to .47g/cc, 6200 m/s to .55g/cc. 5000m/s.  All cut from the same board.

It was the last one... very high density, very poor speed of sound, that I though was the most "interesting".  The grain was visibly different... very wide orange fall growth.  Here are some microphotos:

sitka4.jpg.d9efe48474f7d871d109b48e60af56c7.jpg

The grain on the left shows the wide orange stuff that tends to be dense with low speed of sound, vs the grain on the right which is more reasonable in density and properties.  The upper portion is planed with a very sharp plane, but the thin-wall spring growth still gets mangled and looks white due to scattering.  The lower portion was sliced with a freshly sharpened chisel, which was necessary to show cell detail in closups.

"Normal" grain: sitka1.jpg.e658153f85f59eee16838c929996ada7.jpg

Dense grain: sitka2.jpg.614a8e83f2357ff56ca63a488d7ffef1.jpg

same scale; with a pencil dot in the middle.

Close up of "bad" grain: sitka3.jpg.6863e789d0c9cedccf20b986204f3412.jpg

Shows the extremely thick cell walls, and LOTS of them.

Again, most of this isn't really all that new, just reinforcement of what I had seen previously.  And maybe some more detail.  If I see spruce with wide orange fall grain, I'll avoid it for sure.

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4 hours ago, Anders Buen said:

Have you waxed the end of the grain there?

No; at this magnification, any wax would cover over everything.  Just naturally reflective cellulose, and the lighting is from a concentric LED ring.

1 hour ago, Michael_Molnar said:

I’ll hazard a guess that it due to late, long warm weather. If right, it bodes terribly with advancing climate change. 

I too have been wondering what conditions would cause this (unless the tree just occasionally goes whacky for some other reason).  Presumably the sun doesn't change, leaving temperature and water as the remaining variables.  I too would guess late warm weather is the main thing.  It would be interesting to compare same-species rings from high, cold locations to low, warm ones, and see if that is the factor.

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I sent a link to this thread to my significant other. She does what I call "tree-ring research" for a living. Her immediate reply was: 

<<Looks like compression wood (growth reaction of the tree stem to mechanical stress). Many cells with thickened cell walls and roundish shape in a number of consecutive years argue for that>>

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2 hours ago, kessi2 said:

<<Looks like compression wood (growth reaction of the tree stem to mechanical stress). Many cells with thickened cell walls and roundish shape in a number of consecutive years argue for that>>

The board I have shows bands of the thickened cells, usually 2-4 rings together, each band separated from the other by many years.  The thickened rings start and stop quite suddenly.  Those features don't seem likely for a mechanical stress cause, but more likely something in the conditions.

Similarly, it would seem that some change in the surrounding forest might start suddenly, but likely take many years to slowly change.

For this particular board, it makes most sense to me that the cause would be a weather pattern that can start and stop suddenly and last a few years at most.

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10 minutes ago, GeorgeH said:

If a large branch or branches broke suddenly, and redistributed the balance of the tree, couldn't that cause mechanical stress that would take a few years for the tree to adjust to?

I'm not a tree expert, but it seems to me that the recovery would happen very gradually for a giant Sitka tree such as the one my board was cut from.  As I said, the start and stop is quite sudden for these odd rings.

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<<The described pattern of intermittent 2 to 4 years of these large, colored rings would be consistent with compression wood. It could have been caused e.g. by landslide or solifluction (which both are a change in conditions).

While weather patterns will influence tree ring width and density, they would rather not cause a change of the cell structure to roundish shape and markedly thickened cell walls as shown in these pictures.>>
 

That is me wording the opinions of my SO. I would never be able to tell that from these pictures.

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On 6/21/2021 at 12:18 PM, kessi2 said:

<<The described pattern of intermittent 2 to 4 years of these large, colored rings would be consistent with compression wood. It could have been caused e.g. by landslide or solifluction (which both are a change in conditions).

Concur, and would add earthquake ground changes. 

Also, if one tree starts to fall, it can get caught by another, causing stress on the tree it hits, then suddenly get shoved loose by a windstorm, and relieve the stress.  I've seen "leaners" in my own woodlot stay put for years, then suddenly fall. :)

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12 hours ago, Marty Kasprzyk said:

So how does all of this affect the violin's sound?

Speculation: the same as using spruce that is dense with a low speed of sound.  Theoretically not as loud and responsive as you might get with better wood.  As for the effect of having just some narrow bands of this grain, who knows... maybe not too bad if it's at the edges, but I'd really avoid having it anywhere near the centerline.

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That is certainly reaction wood (called compression on softwoods). I've played number of flat top guitars made with wood that had much wider bands of compression wood than yours and they played nice... but on flat top with the heavy bracing, bridge plate and bridge glued to top, the top makes much smaller part of the whole.

I've got one mandolin top carved out of reaction spruce firewood. I'm not sure I will use it, but once I have a scrap back to match I will certainly give it a go.

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Extreme variations can have a lot of causes. If between section A and section B are 50 years or so we need to see as well that the tree might have gained more height being more exposed to wind at the top. If the piece was cut somewhere in the middle, I would think it is the zone where most stress is visible in the grain structure.  (Just to add some more educated guesses)

I suppose we have to live with the fact that wood is not like plastic, a homogeneous material.^_^

If it comes to choose a good piece for a violin top maybe only the 2cm at each side of the joint really matter. (I would call it the 'sirloin' of spruce)

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1 hour ago, Andreas Preuss said:

If it comes to choose a good piece for a violin top maybe only the 2cm at each side of the joint really matter.

I agree about that being the most critical area, certainly for static stress and in my observation higher-frequency radiation as well.  It is unfortunate that the Strad3D mode animations are blocked out by the fingerboard, as that is one area that I'd really like to see to confirm (or debunk) my observations.

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Thank you for sharing these observations.

I would think the way to deal with this is just to learn to recognize the bad character of wood and avoid using it.

Understanding why it occurs might be nice, but unless you're  harvesting tone wood I doubt it matters much.

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19 hours ago, Don Noon said:

I agree about that being the most critical area, certainly for static stress and in my observation higher-frequency radiation as well.  It is unfortunate that the Strad3D mode animations are blocked out by the fingerboard, as that is one area that I'd really like to see to confirm (or debunk) my observations.

I think it is the whole upper part of the instrument, so the upper part of the top can’t be seen without the upper part of the back. 

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