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12054Reaction wood? (was: early period turned cup)

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  • conradh@efn.org
    Dec 20, 2009
      On Sat, December 19, 2009 7:49 pm, n7bsn wrote:

      > That makes a certain amount of sense. Traditional Scandinavian bowl
      > turning is end-grain not face. We don't really know for certain how far
      > back that goes, or how extensive an area that tradition covered. It's
      > certainly possible it covered Yorvik and Anglo-Saxon England.
      Easy enough to tell. Has anyone thought to check those conical waste
      cores from the turner's shop at Jorvik?

      Using a plug would would make a great certain both stop the end-grain
      > leaking and remove the "pith" that is so often the source of cracking.
      > One more point, it unlikely that they were actually using limb wood. The
      > stresses in limb wood cause large sections of "reaction" wood, that is
      > one side of the limb as a different density then the other side, thus
      > reacting differently.

      Not too sure that one is true. I know all the books here say that, but
      then all the books here also say you shouldn't use end grain turning! How
      much of this is "natural law" (the wood simply won't work that way) and
      how much is simple "everybody knows" lemming behavior? I ask this because
      when I first started turning, I had no instructor. I used _mostly_ limb
      wood, from tree prunings, and some of the pieces came out just fine!

      I certainly have seen asymmetrical seasoning in "reaction wood", but also
      seen it in main-trunk wood, especially in wood from lumberyards.
      Remember, when you didn't cut the tree yourself, you have no way of
      knowing whether that piece of lumber came from a tree that had leaned 20
      degrees, grown resisting the pressure of strong prevailing winds (there
      are places in Oregon where the trees only have branches on one side from
      the wind!), or whether the trunk was stressed by having all its branches
      growing toward the light on the edge of a clearing. I'm not saying that
      "reaction wood" can't be a problem, but rather that it's a problem not
      confined to limbwood, and that quite often the resulting products are
      _still usable_.

      If every face-turned bowl or cup were made from a perfect, riven slab,
      this might be more of an issue. In the real world today, most of them are
      made from slash-sawn planks from a largely automated sawmill run by a
      company that doesn't give a damn. When we buy, we can look at the grain
      and surface knots, but especially in thicker pieces we may be looking at
      almost as much of a crapshoot as the limb-turner faces--and the limbs are
      available at firewood prices, or free for the taking!

      Today it can make sense to cut limbs into blanks, do a very quick and
      rough hollowing, and set them aside to dry. The ones that come out OK get
      fancy finishing efforts and can be lovely pieces; the ones that warp badly
      or crack go right back to the firewood pile from whence they came. IMHO
      it's worth considering whether period woodworkers may have done the same.

      Another bit of evidence that prejudice against reaction wood is far from
      universal--look at the traditional craftsmen who deliberately seek or
      create it. Boatbuilders valued pasture oaks for the "grown knees" that
      could be sawn out where large curved limbs joined the trunk. This wood
      was used for some of the most important structural parts of boats and
      ships, where quality was important and tight fits essential. Handle
      makers all over central Europe, and occasionally elsewhere, would tie
      saplings or limbs into curves and leave them that way, coming back several
      years later to cut custom-curved handle wood. I'm sure that such wood
      reacts and moves as it dries--but I strongly suspect that these people had
      _skilled knowledge_ of the wood's behavior. That the reactions were
      largely predictable, to someone who had been doing this work
      professionally for many years, perhaps?

      Just a thought--we may be seeing craft-revival books that are echoing the
      prejudices and working rules of precision cabinetmakers and joiners when
      they suggest avoiding limb wood. Green woodworkers in period may have had
      an entirely different set of priorities.

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