Paper Conservation: Decisions & Compromises

The Use of NIR Spectroscopy to Investigate the Condition of Parchment
Paul Garside | Barry Knight
British Library, London, UK
Abstract
Parchment documents and manuscripts represent
an important part of our written heritage,
but are prone to a variety of degradative reactions
and so are inherently vulnerable. The ability
to monitor the condition of parchment and
assess the way in which it responds to the environment
allows the most appropriate conservation,
display and storage strategies to be adopted,
and will help to ensure the survival of these artefacts
for future generations.
Near infrared (NIR) spectroscopy provides a
non-invasive (and, with the correct equipment,
potentially in situ) method of investigating the
chemistry of parchment, and has been used in
the work presented here to both assess the progress
of two common deterioration mechanisms
for this material (gelatinisation and thermally
induced cross-linking), as well as to better understand
the way in which it responds to changes
in the local environment (particularly humidity).
Correlations were drawn between physical
changes observed in the parchment samples, as
they were subjected to degradative reactions or
environmental variations, and changes in the
spectra measured by derived peak intensity ratios.
These ratios then allow similar processes to
be monitored in other such materials. A further
outcome of this work has involved applying these
techniques to assess the differences in behaviour
with respect to local conditions between single
parchment sheets and books of bound parchment
leaves, in conjunction with data recorded
by temperature-humidity loggers, and this is of
particular interest when compared to similar results
for paper.
The work has stemmed from questions posed
by objects in the British Library’s collection,
and has been used to better understand these
artefacts and aid collection care decisions. Furthermore,
the environmental response data will
help to inform strategies for the storage of both
individual parchment items and the collection
as a whole (not only benefiting their long-term
survival but also potentially allowing energy and
financial savings).
Introduction
The British Library’s collection contains many
thousands of parchment documents and volumes,
including such important and prestigious
artefacts as the Magna Carta, the Lindisfarne
Gospels and the St Cuthbert Gospel. As items
such as these are of great historic and cultural
significance, preserving them for future generations
is of great importance, and to do this it is
necessary to understand their current condition
and there likely ongoing behaviour. Traditionally
this has been the province of the expertise
and experience of individual conservators and
curators, but with the increasing availability of
analytical equipment it is now possible to supplement
this knowledge with instrumental techniques
that can allow objects to be rapidly investigated
and assessed, permitting those items in
need of greatest attention to be highlighted and
thus selected for attention. With increasing demands
on budgets and time, growing collection
sizes and, in many institutions, fewer specialist
conservation staff, techniques like this which
allow resources to be employed most efficiently
will come to be of ever greater importance.
Parchment is prone to damage from a variety of
causes, including gelatinisation due to exposure
to excessive levels of moisture, microbiological
attack (usually also linked to humidity), physical
damage including general wear-and-tear, embrittlement
from desiccation, and distortion and
shrinkage caused by the extreme temperatures
of fires. Gelatinisation is a common problem
for parchment documents, resulting from the
hydrolysis of the highly ordered and relatively
durable collagen protein to the amorphous and
physically weak gelatine. Parchment documents
are also significantly more susceptible to the
effects of fires than the equivalent paper documents
(Fig. 1); the material contains a variety of
residual oils and fats which will readily burn if
exposed to a flame, and at high temperatures the
bulk material will shrink and distort, not only
resulting in the loss of information from the document,
but also exposing more of the material to
ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013
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