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Hi Bev & All,
Drawing on memory, a thin layer of outer bark is generated each year
just outside of that brown layer and I refer to a fairly thin layer
representing 3-4 years. So the bark cells are under tangential tension.
It is not differential loss of water because when a thin layer is peeled
off and left exposed to room air the darker side sometimes forms the
inside of the coil.
Perhaps the outer (more pale) sides are under greater tangential
tension and contract more when heat decreases adhesion between layers.
These bark cells stop growing in the year they are generated (I
think) and the necessary increase in cell length as the tree grows is
due to their being pulled longer. And when trunk growth eventually
splits the outer layers I think the free ends always curl pale side in.
And I checked only a dozen or so pieces of bark from the box so it
may have been coincidence of wood pretreatment.
Yt, DW, Kentville
------ Original Message ------
From: "Bev Wigney" <bkwigney@gmail.com>
To: naturens@chebucto.ns.ca
Sent: 1/16/2019 6:25:22 PM
Subject: Re: [NatureNS] White Birch bark outside becomes inside of strip
>David and all,
>
>I hope I am understanding this question as meant. Would the curling
>action be because the white outer bark is damper and so dries out more
>(more shrinkage) and also that it is more fragile? I'm thinking of
>the canoes and various other birchbark objects (round containers,
>moose calling horns, etc..) I have seen made by Todd Labrador, and the
>white outer side of the birch is always on the inside. I guess there
>is also a time when collecting bark - in early spring - when the bark
>comes away with an inner layer -- winter bark -- that oxidizes,
>turning dark brown -- and can be etched for designs. I don't know
>all that much about such things, but I follow Todd's work on Facebook.
>It is quite beautiful and fascinating.
>
>Bev,
>Round Hill
>
>On 1/16/19, David <dwebster@glinx.com> wrote:
>> Hi All,
>> I have recently been burning some White Birch and sometimes set
>> aside some bark to pep up a low fire.
>> When layers of bark are stripped off of a stick, whether thick or
>> thin, the outer surface is more pale (white) than the inner. When held
>> near a flame the bark curls and the paler outer side always forms the
>> inside of the curl whether the pale outer side or the darker inner side
>> faces the flame.
>> Why does the outer surface always form the inner side of the coil ?
>> Yt, DW, Kentville
>>
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