Paper Conservation: Decisions & Compromises

Characterising the Origin of Carbon Black Inks by ATR FTIR Spectroscopy
Paul Garside | Rajabi Razak
British Library, London, UK
Kulliyyah of Architecture and Environmental Design, International Islamic University, Malaysia.
Carbon black inks have been used in Asia for
millennia and, therefore, are found in many
documents of historic significance. The source
of carbon for these inks varies with period and
location, and so can provide important information
about the origins and nature of such manuscripts.
The work presented here details the use of
attenuated total reflectance (ATR) infrared spectroscopy
to aid in differentiating these materials.
To this end, five inks were prepared using the
following carbon sources: ivory, bamboo, coconut
and lamp black, made up using traditional
techniques, along with a modern high purity carbon
black. The inks were applied to rag paper,
modern printer paper, pure cellulose paper and
parchment. Subtle differences between the spectra
recorded from the samples (emphasised by
applying spectral subtraction and other enhancement
techniques) could be linked to the source
of the carbon and arise from incompletely burnt
residual material, allowing their origins to be
more accurately determined. These differences
were not observed with the higher purity modern
materials, in which little or no residual material
exists. When this method was applied to
objects using carbon inks of this kind, in many
cases it was possible to determine the likely basis
of the ink.
This technique presents a valuable method for
investigating the provenance and composition
of these historically important inks, and thereby
gaining a greater understanding of the objects
on which they have been used.
Introduction
Pigments and inks based on carbon black have
a long tradition of use, particularly in Asia,
and therefore are found in many documents of
historic and cultural significance. The material
used to make up these pigments is derived from
the soot resulting from the incomplete combustion
of a variety of fuels, including plants, ivory,
bone, lamp oils and waxes (Eastaugh et al. 2008).
Knowing the source of the carbon black can provide
valuable information about the provenance
and history of the document in question, as well
as giving clues to modifications or alterations.
The work presented here details the study of
such inks by ATR spectroscopy, with the aim of
identifying their source by characterising residual
material in the soot.
Method
Finely ground carbon samples from burnt bamboo,
coconut, ivory and lamp oil, as well as a
modern carbon black pigment, were made up as
inks by combining roughly 0.2 g of the carbon
and 0.1 g gum in 5 ml water. A brush was then
used to apply these five inks to four different
substrates: filter paper (pure cellulose), rag paper,
printer paper and parchment.
Once the inks had fully dried, spectra were
recorded from these ink specimens and from the
substrate itself, using a Perkin-Elmer ‘Spectrum
400’ spectrometer fitted with an ATR accessory,
with 16 accumulations and 4 cm -1 resolution. In
each case, two sets of spectra were recorded, the
first using a diamond ATR crystal and the second
a germanium crystal, the former over the range
4000-550 cm -1 , and the latter over 4000-600 cm -1
(the difference being due to the transmission
ranges for the crystals).
For each sample and ATR crystal type, the pure
substrate spectrum was subtracted from those
of the ink on substrate, giving a spectrum of the
residual material in each case.
In order to assess the usability and value of
this approach, carbon inks on four documents
(labelled as X1 to X4) were assessed in a similar
way (subtraction of substrate spectrum from inkplus-substrate
spectrum, followed by interpretation
of the result), and the material origin of
the ink thereby proposed. This assessment was
carried out using the germanium ATR set-up, for
reasons discussed below.
Results and Discussion
The original and subtracted spectra for each of
the five types of ink, recorded using the germa-
ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013
145