I decided to get the straight skinny from the horses mouth: Forest = Products Lab. I found this overview on drying which mentions steam = kiln, hot air, microwave, solar and some weird other methods.=20
One was azeotropic drying, which is boiling in oil. Honest! The said it = produced checking in hardwoods, but if boiled in a vacuum chamber it had = better results.=20
They also mentioned solvent drying, "The solvent seasoning process = involves subjecting the wood to a spray or continuous immersion in = either hot acetone or a similar solvent miscible with water for a number = of hours until most of the water is extracted from the wood." Sounds = similar to LDD processing.=20
No mention of LDD or boiling in water. See: =
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may be more at FPL, but I could find it. My searches came back 0 =or too many to search through. Dan
Not so sure on that one. Checks form when there is too steep a moisture gradient between the surface and the interior. The cells losing bound moisture contract, while their brothers in the same fiber remain fully expanded. FPL covers this under kiln degrade, I believe. Neat thing about checks is that they are self-limiting, depending on the wood and RH. At the point where loss rate exceeds capillary draw, no more rapid drying can take place, because the column of water is broken. Thus the phenomenon we've noticed on our woodpiles, that different woods check deeper than others, even when side by side.
With the microwave, and to a certain extent, a piece heated through-and-through by boiling, I should think what you're doing is helping push water more rapidly to the surface by higher interior vapor pressure over and above the capillary draw that normal surface tension and pore size allows. The micro, as we know, excites molecules and makes the inside (insulated) warmer than the outside, which in concept, at any rate, would make the method superior to through-and-through in the initial stages of heating, and for a short time after removing the piece from boiling.
At what point unraveling the lignin cross-linking becomes more important in the equation is something I would like to find out more about. It could be that it takes time for it to unwind, thus favoring the longer heat period - boiling - over the shorter, but hotter microwave.
Oh yes, topical LDD, which reduces capillary draw, should break the pull earlier, limiting the depth of checks. Maintaining in a miscible solvent or vapor (some folks use alcohol, as I recall) for a long period of time merely increases the vapor pressure from within, mimicking the microwave process.
More on point is that this is exactly what happens when steam bending wood. Perhaps boiling's success isn't that it lets wood dry faster, but with less checking?
George, A lot of interesting points and new questions, for me, too. The = only thing I can contribute is steam bending. I've done a fair bit and = have the Wood Bending handbook, too. The rule of thumb is that it takes = one hour per inch of stock thickness to prepare wood for bending at a = tad under 212=B0F. Of course this heating effect is not linear. Veneer = can be heated almost instantly. Dan
We used to do snowshoe bends (1x1) for an hour, so seems a fair rule. I've seen luthiers and makers of Shaker boxes bend over hot pipes with soaked wood, and that nearly veneer thin, which may or may not disprove the hypothesis.
I've got to get me a better cushion for my shave horse. You would think that the excess adipose tissue would cushion well enough, but I have to change contours too often. Oh well the alternative to old is dead, so I guess I'll make a quick addition to the sharpening thread before I take my extra cushion and the rest of this ice tea outside.
If you come up with some science, let us know, eh?
George, A lot of interesting points and new questions, for me, too. The only thing I can contribute is steam bending. I've done a fair bit and have the Wood Bending handbook, too. The rule of thumb is that it takes one hour per inch of stock thickness to prepare wood for bending at a tad under 212°F. Of course this heating effect is not linear. Veneer can be heated almost instantly. Dan
One other thing to note about using a steel drum to boil. If there is tannin in the wood the water and wood will turn black/dark brown It's just like making the vinegar/iron mixture to ebonize wood This dark layer is very very thin and turns off easily.
One other method I heard about at a demo was to soak the item in alcohol (ethanol) overnight. This was done on a turned item with minimal thickness. It was said to dry the wood very quickly. The demonstrator had a few examples. I believe that he attributed it to Dale Nish but I can't even remember the demonstrators name more or less who he said gave him the idea.
I'm assuming this is utilizing the hygroscopic nature of alcohol. Following that line of reasoning, couldn't one also use a concentrated solution of sugar water? The osmotic gradient would be in favor of pulling the moisture out of the wood, I'd think.
I think in a nutshell Russells protacol calls for boiling 1 hour per inch of thickness as a minimum. Hes says it can go longer. The big thing is when you start your watch. if the water is boiling and you drop in your bowls the boiling stops. The hour stars when you have a rapid boil again. Same for adding water. The clock runs when the water is boiling again. I have not tried this yet still doing LLD, but I have heard him explain it several times. Most detail would be his web site that has been posted.
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