[NHCOLL-L:474] unrolling birch bark scrolls

[Emily Kaplan]

I am posting this for a colleague not on the list and I apologize for cross-posting. Replies can be sent directly to Marian Kaminitz (address below) but it would be great to have them sent to the list for all to see. 
Emily Kaplan

Unrolling birch bark scrolls

The conservation lab of the National Museum of the American Indian was recently asked to unroll 11 Ojibway birch bark scrolls which have been in the collection since the early 1930's so that Ojibway Elders can view and interpret them.
The scrolls are between 7" and 19" in width, 15" to 79" long and they vary in thickness.  All of them are currently rolled up more or less tightly, with the paper side in, which is also the side that is inscribed.  On some of them, red pigment (red ochre or vermillion) has been rubbed onto the surface.  All of them are presently too stiff to be unrolled without relaxing them first.  However, after testing the most commonly used methods to relax and unroll birch bark, it appears that there is no gentle way to do this. 

On rolled sample material, some of it rather old, we tested:
- unrolling during exposure to dry heat from a heat gun
- unrolling during exposure to ethanol / methanol vapors
We did not test steam yet, because initially it seemed to be the least conservative method.

Damages that occurred during testing are as follows:
With dry heat:  
- Strong delamination / separation of the paper from the cambium bark  layers
- Breakage of paper side layers, causing flaking
- Splitting in the lengthwise grain
- It is easy to scorch the bark

With ethanol / methanol vapors in an enclosed environment:
(The red pigments have been tested and should not be affected by solvent vapors)
- Delamination / separation of bark layers, somewhat less pronounced than with dry heat
- The lenticels (=the characteristic lens-shaped pores in the bark) propagate lengthwise tears that extend into the rest of the bark sheet
- Blanching of the bark during exposure to solvent vapors, especially with ethanol

We are wondering what experiences other conservators had with unrolling birch bark and what method worked best for them.  Also, did anyone try to remove blanching products from bark that were caused by exposure to solvent vapors?  Did anyone observe damages similar to our test results?

We sure would appreciate your input!  Thank you!


Marian A. Kaminitz
Head of Conservation
National Museum of the American Indian
Cultural Resources Center
4220 Silver Hill Road
Suitland, MD  20746
phone: 301-238-6624 ext6322
fax: 301-238-3201
email:   kaminitzm at nmaicrc.si.edu