Paper Conservation: Decisions & Compromises

Fig. 2: Changes related to thermal damage in the
NIR spectrum.
Fig. 3: Changes related to gelatinisation in the
NIR spectrum.
with a resolution of 16 cm -1 and averaged over 50
accumulations.
Results and Discussion
Examining the spectra shows that the thermally
damaged samples display a characteristic change
in the region 4700 - 4200 cm -1 (Fig. 2). It can be
seen that as the sample suffers thermal damage
the strength of the peak at 4420 cm -1 diminishes
with respect to the neighbouring peak at 4540
cm -1 ; furthermore, the shoulder observed at 4920
cm -1 loses definition. Using these observations,
it is possible to derive a spectral intensity ratio
that reflects this change and can thus be used to
investigate regions of thermal damage:
D D
= I 4540
/ I 4420
Where: D D
= indicator of thermal damage
I x
= intensity at x cm -1 , above a baseline
drawn from 4680 to 4150 cm -1 .
The changes involved in the early stages of gelatinisation
are more subtle, but can be seen if
the broad peak at 7300 - 6100 is considered (Fig.
3). The general shape of this peak changes as
gelatinisation occurs, with the primary peak at
6860 cm -1 diminishing and a secondary one at
6685 cm -1 becoming more apparent. As above, an
intensity ratio based on this observation can be
used to assess the degree of gelatinisation in a
parchment sample:
D g
= I 6685
/ I 6860
Where: D g
= indicator of gelatinisation
I x
= intensity at x cm -1 , above a baseline
drawn from 7540 to 6030 cm -1 .
If a sample is prepared in which localised gelatinsation
has been encouraged by the use of a dampened
swab, or which has been partially burnt,
then these ratios can be derived from spectra
recorded systematically across the specimen and
displayed as a colour scale, indicating the areas
in which damage has occurred and thereby demonstrating
that this approach can be used to map
such damage.
Conclusion
NIR spectroscopy is a valuable tool for the investigation
of historical and cultural artefacts, as
it can be used a non-sampling, non-invasive, in
situ manner, and is rapid and simple to employ.
With this work we have demonstrated how the
technique may be used to investigate the state of
parchment, in particular the onset of gelatinisation
and thermally induced damage. This will
ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013
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