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Monday, August 15, 2016

Wood Science 101 (26) - The Wood-Wide Web

Most of us that have studied the cellular structure of wood know that the topic can be a bit, well, dry. There are dozens of technical terms that mean nothing outside a wood technology textbook, coupled with line drawings and pictures that try to give the reader a sense of how all those cells go together and grow. But, like the study of physics, it's all a bit difficult to grasp when looking at a tree or running your hand along the smooth arm of a wooden rocker.

But one woodworker has stumbled on to a wonderful way to visually display how a tree really goes together. He started out by applying his love of wood turning to the task of seeing how thin a cross-section of wood he could turn. Once he had his extra-thin disc, he probably noticed that the less dense early wood tended to crumble away as he got too thin...leaving a web-like skeleton of a tree in his hands. Being an electrical engineer, he was probably familiar with the high-tech machines that are used to put a fine sand-blasted finish on circuit boards to eliminate any extra solder or fiberglass that could impair the functioning of the circuits. Ingenuity being what it is, he probably thought to himself...hey, I could use a circuit-board sand-blaster to knock out all this early wood, and it would look real neat.

Well, he was right.

The art work he's produced does look amazing, but to us at Go Wood the real value of his work is to bring all those wood technology drawings to life. The web produced by the intersection of the medullary cells (we generally just call them rays) with the remnant ring of dense late wood cells gives us a visual sense of just how the strength of wood is accomplished. Imagine this wood web a hundred thousand or so layers thick, and you have the stem of a tree. No wonder it's so strong.

Here's a picture of oak cells for comparison with the wood "lace" in the video.

Ring-porous hardwood illustrating the abrupt change in diameter of earlywood (EW) and latewood (LW) vessels as seen in cross-section. Between the latewood vessel zones are thick wall fibers (F). Wood rays are apparent on all three surfaces (arrows). Source: Wood: Its Structure and Properties, F.F. Wangaard, ed. 1981.

From the picture, we can see that the earlywood being removed with the circuit-board sand-blaster is very porous, and that the latewood bands that are left are held together by the thick wall fibers. Thus, the spidery bands of remnant wood we see in the video.

Any guess, then, why the art works in the video are being performed on oak? Well, in softwoods and diffuse-porous hardwoods, there is far less differentiation between the earlywood to be removed and the wood to remain. Take a look at this picture of a diffuse-porous hardwood.

Diffuse-porous hardwood showing the rather uniform diameter of vessels throughout the growth ring. In both the tangential and radial views the formation of vessels from individual vessel elements (E) is clearly illustrated. Note the presences of both one-cell wide and multi-cell wide rays in the tangential view (arrows). Source: Wood: Its Structure and Properties, F.F. Wangaard, ed. 1981. 

Note in the above photograph that if the uniform bands of vessels were removed through sand blasting, there would be little if anything left of the wood. So, a ring-porous, large-rayed wood such as oak is the perfect choice for the type of work being performed by the artist. Other woods that might be good candidates are chestnut, hickory, elm, ash, osage-orange, and locust.

You might think that heavy, dense diffuse-porous woods, such as many of the tropical species, would also be good candidates for this type of wood-turning skeletonization. But the sand-blasting process would have to be done on individual cells, not on bands, so that already tedious process would become extremely tedious.

So, now you know what the inside skeletal structure of a tree really looks like, and how it is all engineered by nature to support the tree's weight.

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