I don't know if this will answer all of your questions, but this
has
been asked a couple of times on the tree-ring forum:
http://listserv.arizona.edu/cgi-bin/wa?A2=ind0310&L=ITRDBFOR&P=R2465&I=-3
Date:
Wed, 29 Oct 2003 08:21:30 -0800
Michael Murray is interested in dimensional stabilization:
>We recently acquired a large (5 ft. , 1.5 m) cross-section
of a sugar pine >(Pinus lambertiana) snag estimated to be
about 520 years old. We'd like to >use it as a display for
the approximately 500,000 people who visit our Park
>annually. >Currently it is drying. We've tightened three
steel bands (2cm width) >around its circumference to keep
from cracking and falling apart. >Does anyone have advice on
long-term stabilization and preservation? >That is, should
larger metal bands be used + where can we obtain, how to
>apply, etc.? >Also, after sanding smooth, is there a
recommended preservative/protectant >method?
The standard treatment for dimensional stabilization of most
wood is to treat it with polyethylene glycol (PEG), a chemical
substance related to antifreeze. Treatment method is to soak the
wood sample in a solution of PEG and water for a period of about
two months, then to remove the sample to a well ventilated area
for drying for another two months. The result is a piece of wood
that doesn't alter its dimensions greatly in response to
fluctuations in its environment, i.e. it doesn't crack. The
drawback is that the end product has an altered appearance,
looking generally darker (at least among pines) and having a
waxy texture and a distinct PEG/antifreeze odor. Of course,
since your sample is from a snag it might already have a
distinct appearance, texture, and odor, and treating with PEG
may be an improvement over that. I have seen samples of old
growth longleaf pine from south Alabama that were simply cut,
dried, and then treated with a thick polyurethane finish. The
specimens mostly retained their original appearance, but did
develop cracks as time went on. This treatment is probably your
best approach in combination with the metal bands you mentioned.
Some cracking seems to be inevitable, though. Another idea to
consider, intellectually, at least, is to put the sample in a
glass case in which the ambient air has a higher moisture
content than the wood sample. This will eliminate the water loss
from the wood sample, though it would promote the growth of just
about every fungus spore currently on the sample. While I have
seen displays of this sort here and there, I am not aware of a
standard procedure for how such specimens are preserved.
Hopefully one of the other list members can pipe in with
additional recommendations.
Matthew C Anderson
Forest Biometrician Mason, Bruce, & Girard, Inc. 707 SW
Washington Street, Suite 1300 Portland, Oregon 97205
http://listserv.arizona.edu/cgi-bin/wa?A2=ind0310&L=ITRDBFOR&P=R2972&I=-3
Date:
Thu, 30 Oct 2003 15:27:16 +0100
Dear Michael and all forum members,
Last January I asked the same question. From the answers I
received then I wrote a summary and posted it to the forum. I'm
attaching it below. In addition, we knew of a wood importer who
is able to dry large pieces of wood in a controlled environment
so that they don't crack. The method, he knows. So, a good
option may be contacting a wood dealer in your area. If your
sample is partially decayed, however, I guess the best option
would be the PEG impregnation, but I don't know the details of
this method (which type of PEG -there are a lot of them-, what
concentration, etc). The archaeologists will probably help you.
Here is the summary of previous answers to the question of how
to dry large cross-sections:
1- Making a radial saw cut at one radius (from bark to pith).
While drying this will be the only enlarging crack because it
will relieve the tension from the whole disk, thus preventing
both large irregular cracks and small cracks from forming
throughout. This is a convenient solution if the perfect
entirety and roundness of the cross-section is of course not
absolutely essential.
2- Coating the wood with wax for slow drying, and binding the
sample around with steel strap. The wax technique may have a
long history, as it seems it's being used by violin makers since
long ago.
3- Putting something into the wood to occupy the space
formerly occupied by water. This should be a low-mollecular
weight compound, preferably PEG (polyethylenglycol). PEG is a
waxy compound that can be dissolved in water, and the solution
can be applied to the samples by painting or soaking them in.
Several iterations and increasing PEG concentrations or
different PEG types may be required so that the wood gets
saturated with PEG. This process may take even months. At the
end the sample can be air dried. The PEG will remain within the
wood, stablising its structure and preventing it from shrinking
and cracking, as well as probaby from being attacked by fungi
and/or insects.
4- (This one in the Dendro FAQ, here summarized) Fresh wood
samples should be placed soon into 100% ethanol . This helps to
preserve the wood by preventing fungal growth, and facilitates
the drying process. In addition, ethanol will replace all the
water in the wood, which will avoid the problem of collapse and
checking: Ethanol should be replaced at least 3 times over the
next 2 weeks. Prior to air drying the samples should be refluxed
in ethanol over a six hour period, to complete the water removal
process. Samples can then be air dried and stored. This
treatment will result in minimal dimensional changes between the
green and dried conditions. The larger the sample the greater
the time needed to replace water with ethanol.
Note that for chemical analyses this method may be
inapropriate since ethanol may remove some extractives from the
wood.
Regards, Oriol Bosch
Departament d'Ecologia Facultat de Biologia Universitat de
Barcelona Av. Diagonal 645 08028 Barcelona, Catalunya (Spain)
Hope this helps,
Neil
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