the fire (on the other hand paper, unless found as loose sheets, tends to remain as a solid block, which chars around the edges but does not read-ily burn). One of the collections on which the Library was based, the Cotton collection (origi-nally belonging to the 17th century antiquarian Sir Robert Cotton) was involved in two fires, the first in 1731 and the second (smaller) one in 1865, which caused significant damage to many impor-tant documents, including Beowulf and a copy of the Magna Carta.
Some cases of these types of damage are read-ily apparent - taken to an extreme, gelatinisation results in a material with a typical translucent, glossy appearance, and fire damage causes obvi-ous scorching and distortion. Not all degrada-tion is so obvious, and early stages of deteriora-tion can be difficult to detect. Even at such stag-es, however, these changes can have a significant effect on the stability of the material and will influence the choices of the most suitable
con-servation treatments and storage conditions. For example, gelatinised parchment is particularly prone to further damage from water, whilst ther-mally damaged material is brittle and prone to physical damage. Therefore it would be of value to the preservation of these materials to have a method of detecting these early signs of damage in order to identify materials at risk and to treat them in the most appropriate manner.
Given the value of the artefacts which may be as-sets, such a technique would have to be non-sam-pling and non-invasive to be of use in the field of conservation; ease of use, rapidity of analysis and the potential to carry out the investigation in an in situ manner would also be desirable. Near infrared (NIR) spectroscopy provides a method which fulfils these requirements, and has there-fore been investigated as a method characteris-ing the state of parchment.
To this end, a variety of different samples were obtained for investigation. Some of these came from historic sources, and thus represent examples of ‘real’ ageing and damage; to widen this set of samples, further specimens were pre-pared by exposing modern parchment to heat, fire or conditions that would induce gelatinisa-tion. These materials were used in conjunction with NIR spectroscopy to investigate measurable changes and thereby develop methods of moni-toring such changes in parchment artefacts.
This research has been carried out as part of a larger investigation into the condition, conserva-tion and assessment of parchment based arte-facts held in the British Library’s collection.
Method
A number of historic parchment samples in a va-riety of conditions were collected for assessment.
In addition, surrogates were prepared in several ways. Gelatinised specimens were produced by placing several different parchment samples in a high humidity environment (90% RH, 40°C), and removing sections daily over the course of a month. Samples were also exposed to fire to yield specimens which mimicked the fire-dam-aged parchment of the cotton collection. These materials were stored at 18°C and 50% RH prior to and during analysis.
Spectra were collected from these materials, using a PerkinElmer ‘Spectrum 400’ spectrome-ter fitted with an NIR integrating sphere; spectra were recorded over the range 12,000 - 4,000 cm-1,
Fig. 1: Fire damage to a parchment manuscript, showing scorching and distortion (the parchment was deliberately cut between lines and col-umns in the 19th C to allow it to be flattened).
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:
DD = I4540 / I4420
Where: DD = indicator of thermal damage Ix = intensity at x cm-1, above a baseline drawn from 4680 to 4150 cm-1.
The changes involved in the early stages of ge-latinisation 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:
Dg = I6685 / I6860
Where: Dg = indicator of gelatinisation
Ix = intensity at x cm-1, above a baseline drawn from 7540 to 6030 cm-1.
If a sample is prepared in which localised gelatin-sation has been encouraged by the use of a damp-ened 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 dem-onstrating that this approach can be used to map such damage.
Conclusion
NIR spectroscopy is a valuable tool for the inves-tigation 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 gelatinisa-tion and thermally induced damage. This will
Fig. 3: Changes related to gelatinisation in the NIR spectrum.
Fig. 2: Changes related to thermal damage in the NIR spectrum.
inform decisions on conservation treatments, handling methods and display and storage condi-tions. Currently this approach is used as a spot analysis technique, but the aim is to developing into an imaging method that will allow parch-ment manuscripts to be rapidly assessed.
Acknowledgements
The authors would like to thank their colleagues at the British Library for their help and support.
Authors Paul Garside
British Library, 96 Euston Road, London, NW1 2DB, UK; paul.garside@bl.uk.
Barry Knight
British Library, 96 Euston Road, London, NW1 2DB, UK.