Storing mounted botanical specimens

The following is posted on behalf of Heidi Elin Myklebost at the
NTNU Museum of Natural History and Archaeology in Trondheim, Norway.

The museum's botanical department has among its collections a large
number--approximately 2800 single sheets--of pressed plants that
have been mounted on paper, both plants and paper deriving from the
1760's. This material (mainly algae, vascular plants, lichen and
fungi) forms the basis of Flora Norvegica, the first Norwegian
flora. In the 1970's, the original mounts were partly attached to
thin yellow cardboard, using an unknown glue. Even though the
cardboard isn't attached completely, the mount is fairly strong. For
each object, there is an outer and detached wrapping in what seems
to be Pergamyn.

The sheets are stored horizontally in paper boxes, in a climate of
about 16-18 deg. C and low but stabile RH (approximately 25%). The
entire collection has been digitized and the objects rarely leave
their storage facility. Recently and in connection with a
preservation programme, the 1970's cardboard has been tested for pH
and lignin content, indicating a pH value of 4.5 and presence of
lignin.

Samples of the collection have been studied, and apart from some
slight discolouration (mainly deriving from the glue used to attach
the cardboard to the original mount) and general surface dirt, no
visible signs of acidic degradation of paper or breakdown of plant
material (other than that of old age and general wear and tear) have
been found. However, there is concern about the presence of high
acidity.

This brings me to my question: what are the general thoughts on
storage and storage materials for these kinds of objects, including
protecting it from acidic degradation? As the staff will not be able
to remove the 1970's cardboard at present, the storage (material)
must cater for that. Any tips, ideas and suggested further reading
would be most welcome.

Victoria Juhlin
Conservator of Books and Library materials
Gunnerusbiblioteket
Trondheim, Norway


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                  Conservation DistList Instance 23:39
                   Distributed: Friday, April 9, 2010
                       Message Id: cdl-23-39-032
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