Storage environment for parchment

Robert J. Milevski <milevski [at] princeton__edu> writes

>What are the recommended temperature and relative humidity (or
>published standards) for storing bound and unbound vellum and
>parchment library material?  Trolling the Internet and available
>books I come up with only two references. ...

Two published Standards that cover the environment for storing
parchment are: BS 5454:2000 Recommendations for the storage and
exhibition of archival documents, and ISO 11799:2003 Document
storage requirements for archive and library materials.  The British
Standard 5454 section 7 covers environments for paper and parchment,
section 7-3-3 covering RH states "Relative humidity should be at a
fixed point between 45% and 60% with a tolerance of 5% on either
side [of the fixed point]..."

The ISO Standard 11799 Annex B, Table B.1 gives figures for the
variety of materials found in archives and libraries and
specifically recommends the following for parchment (separately from
paper): minimum 50% maximum 60%, plus or minus 3%.

The problem of mixed media archives is not easily addressed by the
ISO standard, since the RH recommendation for paper in regular use
is 35% to 50%, which at the bottom is too low for parchment that may
be taken out and used in a more humid search room for example, and
its recommendation for little used paper is 30% to 45%.  Dry, stiff
parchment is known to suffer damage if manipulated in that state.

Both standards focus predominantly on the qualities of an archive
storage building rather than on the nature of the materials stored,
and both are being reviewed.  If your collection is mixed and is
likely to be used, it is advisable to maintain the environment in
the 50% region and as stable as you can manage, especially on a
diurnal basis, as parchment expands and shrinks very significantly
in changing RH environments.  New parchment can take on 10% of its
weight in water every 30 minutes in a high humidity environment.
Expansion and contraction varies depending on the condition of the
parchment but, for example, I recently noted an expansion capacity
in an 800 year old document of over 2% growth in size for every 10%
increase in RH.  To put that into context, a square document of,
say, 500mm (20inches) along each side can grow 10mm (3/8 inch) in
each dimension when the RH moves from 45% to 55% (and
correspondingly shrinking in a drop in RH).  Inks and illumination
pigments such as gold leaf are at risk of flaking and loss with
significant and regular expansion and contraction.

Parchment can last many centuries in dry conditions but only if not
used.  The greatest common threat to parchment is water or damp
conditions and the mould growth that results, hence the shift away
from 65% in earlier recommendations, where this level was considered
still to risk mould growth in an archive with poor air circulation.
More significantly perhaps, operating at a level in the region of
65% is likely to mean that for part of the time conditions will be
above this, especially when air conditioning fails or passive
control is inadequate in seasons of higher humidity.

If readers of this list will forgive my immodesty, you will find a
comprehensive review of parchment conservation issues and an
extensive bibliography in my chapter on the topic in Conservation of
Leather and Related Materials, edited by Marion Kite and Roy
Thomson, published by Butterworth-Heinemann and IIC, 2006, which you
can get easily from Amazon or other online book sellers.

Understanding the nature and condition of parchment items in your
collection will be an important step in planning storage, excellent
work has been undertaken on the ageing characteristics of parchment
and early warning signs of its decay in a European, EU-funded
project IDAP - Improved Damage Assessment of Parchment
<URL:http://www.idap-parchment.dk>, and its associated book
Microanalysis of Parchment, edited by Rene Larson, also available to
buy online.

Chris Woods
Director
Conservation Ltd and
National Conservation Service
+44 845 156 2103
Mobile: +44 7855 796985


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                  Conservation DistList Instance 23:26
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