Tree Cookie Preservation   Edward Frank
  Nov 24, 2005 18:00 PST 

When visiting various state parks, small museums etc. I often see cookies - cross-section slices of tree trunks - on display. Typically they emphasize the age of the tree section, and may have various dates pinpointed at different rings on the slice. However at most of these places the sections have been varnished. Now with the passing of the years the varnish has darkened to the point that the rings are barely visible. If they are not protected in some way, the wood will oxidize and turn dark itself, not to mention handling it will leave dirt and oils on the sample also obscuring the details of the section.

Is there something available today that would serve the purpose of protecting the wood from handling, that enhances the visibility of the rings, and will not yellow with time? What about various polyurethanes? Should these older slices be redone using newer sealers that don't yellow, and what would be the best way to refinish them? Is sanding the best option to remove the older varnishes?

Ed Frank
Re: Tree Cookie Preservation
  Nov 26, 2005 16:25 PST 

I have a product you could try. I am currently using this on my house. It is called PC rot terminator. It is an epoxy wood consolidant. It stops rot of all kinds, including insects. It is made in good ole Pennsylvania too. Available through ACE hardware, special order. They also make a waterbase solution too. I am very happy with it thus far. No web site that I can find, but lots of info when you google.

Re: Tree Cookie Preservation   Neil Pederson
  Nov 27, 2005 17:47 PST 

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:

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

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,

Preserving large cross-sections   Robyn Darbyshire
  Nov 29, 2005 01:07 PST 

Thanks for the posts on this - I am currently dealing with the same
situation, but for a large sugar pine cross section that weighs about
500 lbs and is over 4 feet across. It was one of the local tree "icons"
that was killed by the 2002 Biscuit Fire and, because of its location
directly above a well-traveled road, it was logged. We have a nice
photo history of it (and it's post-fire slow demise), and now the cross
section, showing that this tree survived girdling on about 60% of its
circumference (presumably by a fire) when it was about 2" in diameter!
We hope to sand it once it is dry and look for other fire scars and
notable events in the tree's life. It definitely pre-dates our other
fire information for that area, so that will be a great addition that
the tree can add to our knowledge now that it has passed on.....
Re: Preserving large cross-sections   Dean Hedin
  Nov 30, 2005 20:38 PST 

Interesting. You got me thinking that it should be a law that logging
operations must slice & catalog sections of large trees they fell for
the use of researchers into climate & environment.

I know that section collections do exist for this purpose already, but they
should just make this a law.

== 3 of 3 ==
Date: Wed, Oct 10 2007 7:40 pm
From: Erie Buoy

Gary --

I've had very good luck stabilizing cross-cut sections of trees with a
product called Pentacryl (
). It's pretty pricey, but from what I gather is a better alternative
than PEG. Pentacryl, as far as I understand it, polymerizes the water
in the cells of the wood. I used several gallons of the stuff to
stabilize a 5 1/2 foot diameter cross section of a 100 year old black
walnut. I moved the cross-section inside last summer, so it's been
through a winter of heated (dry) inside air with only a tiny check.
I'm beginning to consider the project a success . . . thanks to the
Pentacryl, I think. It's best to get the Pentacryl on the wood
freshly after a cut, which I did, but the stump had been sitting for
several months before I made the cut the slab off the top.



On Oct 9, 7:47 pm, "Gary A. Beluzo" <> wrote:
> Ed,
> This might be a good time to bring up how to properly dry the cookie
> so that it doesn't split and can be used for educational purposes.
> ENTS what's the best way to dry a cookie so it doesn't crack and weaken?