Bill C, you don’t have to copy someone else, you do have to understand what happens and how you can control it or at least try.
Trying to keep this simple, see Wood as bundles of straws, they will dry in the air, fast or slow depending on how dry the air is and if it is moving, temperature also influences the drying.
All those straws are held together by a substance that is called Lignin, it is pretty tough stuff or else the wood would fall apart, however heating this Lignin will make it a bit less tough and the straws can move some if they have to.
So as these straws dry they get thinner, not really shorter (one tenth of a procent from wet to oven dry) then we have some straws that are different than the rest, the pith area straws have been fed to grow up fast in the length, while the later straws that are more rigid to keep the stem from falling over and these will become the heartwood, and these get filled with products the tree doesn’t need anymore, then there are the sapwood straws that are full of saps to enable the tree to grow, but still without any of the byproducts of the tree.
So you can see that even if we could let all these straws dry evenly, there is the difference of the type of straws that have some shrink more or less than the other straws, and some of the stresses in drying wood stem from this, as said before heating the wood will let some of these stresses become less.
But even at normal room temperature the straws can move albeit much slower than if heated like in boiling water, so giving the wood enough time the stresses will get lower.
Of course we have another problem when we turn wood in side grain direction and with all shorter pieces of wood where the endgrain is exposed to the air, where the end of the wood will dry fast, but the wood farther from the end will not dry like the wood on the end, and now something has to give, splitting is how the difference in thickness is accommodated .
With a bowl we have this endgrain on two sides of the bowl this wood will dry very fast while the side grain is unable to dry at that speed, so if we now can slow the endgrain from drying any faster than the side grain, we won’t get the stresses from that, or we boil the bowl in water to heat the lignin and enable these straws/wood to move reducing the stresses.
There still will be some stresses but most wood will be able to accommodate these, here is were the pith wood lets us down, it is different than the heartwood and also weaker and will split very easily, often in minutes after being exposed to the air it will start splitting.
I have used brown paper bags to slow down the drying of my rough turned bowls, this works if you can keep the drying slow enough, not every place is identical, but most places people live in are very similar, outside or shops and garages etc don’t have to be,
So a brown paper bag with a wet rough turned bowl will get air in it that becomes totally saturated, and so drying stops, now the paper bag will absorb some of the moisture in the air in the bag, giving the air in the bag to take some more moisture from the wood, air around the bag will take moisture from the bag, and so the paper bag will absorb some moisture from the air in the bag, and so on and on it goes.
By reducing the speed at which the paper bag dries will control the speed of the bowl drying inside the bag, so this is up to you, I have a 99% succes rate or better even with fruit wood like Apple.
For me, I place the bag right on the floor in my basement, where there is no air blowing and no heating from the sun or other, I never add anything to the bag, as this would lay against the wood and prevent the wood from drying, making the grow of mold/fungus very likely, it is something I still check for in the first week or two for, if there is any, I wipe the bowl dry and place the bowl in a dry bag, and close the paper bag, the wet bag can be used again when dry.
Bowls in paper bags
Ash bowls dry
Applewood bowls dry
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