Paper Conservation: Decisions & Compromises
Paper Conservation: Decisions & Compromises Paper Conservation: Decisions & Compromises
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 readily burn). One of the collections on which the Library was based, the Cotton collection (originally belonging to the 17 th 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 important documents, including Beowulf and a copy of the Magna Carta. Some cases of these types of damage are readily apparent - taken to an extreme, gelatinisation results in a material with a typical translucent, glossy appearance, and fire damage causes obvious scorching and distortion. Not all degradation is so obvious, and early stages of deterioration can be difficult to detect. Even at such stages, however, these changes can have a significant effect on the stability of the material and will influence the choices of the most suitable conservation treatments and storage conditions. For example, gelatinised parchment is particularly prone to further damage from water, whilst thermally 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. Fig. 1: Fire damage to a parchment manuscript, showing scorching and distortion (the parchment was deliberately cut between lines and columns in the 19 th C to allow it to be flattened). Given the value of the artefacts which may be assets, such a technique would have to be non-sampling 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 therefore been investigated as a method characterising 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 prepared by exposing modern parchment to heat, fire or conditions that would induce gelatinisation. These materials were used in conjunction with NIR spectroscopy to investigate measurable changes and thereby develop methods of monitoring such changes in parchment artefacts. This research has been carried out as part of a larger investigation into the condition, conservation and assessment of parchment based artefacts held in the British Library’s collection. Method A number of historic parchment samples in a variety 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-damaged 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’ spectrometer fitted with an NIR integrating sphere; spectra were recorded over the range 12,000 - 4,000 cm -1 , ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013 56
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 57
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the fire (on the other hand paper, unless found<br />
as loose sheets, tends to remain as a solid block,<br />
which chars around the edges but does not readily<br />
burn). One of the collections on which the<br />
Library was based, the Cotton collection (originally<br />
belonging to the 17 th century antiquarian<br />
Sir Robert Cotton) was involved in two fires, the<br />
first in 1731 and the second (smaller) one in 1865,<br />
which caused significant damage to many important<br />
documents, including Beowulf and a copy of<br />
the Magna Carta.<br />
Some cases of these types of damage are readily<br />
apparent - taken to an extreme, gelatinisation<br />
results in a material with a typical translucent,<br />
glossy appearance, and fire damage causes obvious<br />
scorching and distortion. Not all degradation<br />
is so obvious, and early stages of deterioration<br />
can be difficult to detect. Even at such stages,<br />
however, these changes can have a significant<br />
effect on the stability of the material and will<br />
influence the choices of the most suitable conservation<br />
treatments and storage conditions. For<br />
example, gelatinised parchment is particularly<br />
prone to further damage from water, whilst thermally<br />
damaged material is brittle and prone to<br />
physical damage. Therefore it would be of value<br />
to the preservation of these materials to have a<br />
method of detecting these early signs of damage<br />
in order to identify materials at risk and to treat<br />
them in the most appropriate manner.<br />
Fig. 1: Fire damage to a parchment manuscript, showing scorching and<br />
distortion (the parchment was deliberately cut between lines and columns<br />
in the 19 th C to allow it to be flattened).<br />
Given the value of the artefacts which may be assets,<br />
such a technique would have to be non-sampling<br />
and non-invasive to be of use in the field of<br />
conservation; ease of use, rapidity of analysis and<br />
the potential to carry out the investigation in<br />
an in situ manner would also be desirable. Near<br />
infrared (NIR) spectroscopy provides a method<br />
which fulfils these requirements, and has therefore<br />
been investigated as a method characterising<br />
the state of parchment.<br />
To this end, a variety of different samples<br />
were obtained for investigation. Some of these<br />
came from historic sources, and thus represent<br />
examples of ‘real’ ageing and damage; to widen<br />
this set of samples, further specimens were prepared<br />
by exposing modern parchment to heat,<br />
fire or conditions that would induce gelatinisation.<br />
These materials were used in conjunction<br />
with NIR spectroscopy to investigate measurable<br />
changes and thereby develop methods of monitoring<br />
such changes in parchment artefacts.<br />
This research has been carried out as part of a<br />
larger investigation into the condition, conservation<br />
and assessment of parchment based artefacts<br />
held in the British Library’s collection.<br />
Method<br />
A number of historic parchment samples in a variety<br />
of conditions were collected for assessment.<br />
In addition, surrogates were prepared in several<br />
ways. Gelatinised specimens were produced by<br />
placing several different parchment samples in<br />
a high humidity environment (90% RH, 40°C),<br />
and removing sections daily over the course of<br />
a month. Samples were also exposed to fire to<br />
yield specimens which mimicked the fire-damaged<br />
parchment of the cotton collection. These<br />
materials were stored at 18°C and 50% RH prior<br />
to and during analysis.<br />
Spectra were collected from these materials,<br />
using a PerkinElmer ‘Spectrum 400’ spectrometer<br />
fitted with an NIR integrating sphere; spectra<br />
were recorded over the range 12,000 - 4,000 cm -1 ,<br />
ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013<br />
56