Determination of elemental concentrations of iron gall ink
components by PIXE1
Miloš Budnar*, Jure Simčič*, Mitja Uršič*, Zdravko Rupnik*,
Jana Kolar†, and Matija Strlič‡
*
Jožef Stefan Institute, p.p.3000, SI-1001 Ljubljana, Slovenia
National and University Library, Turjaška 1, SI-1000 Ljubljana, Slovenia
‡
University of Ljubljana, Faculty of chemistry and chemical technology, Aškerčeva 5, SI-1000 Ljubljana, Slovenia
†
Abstract. The harmful effects of the iron gall ink on the supporting media (i.e. paper, parchment) are known for a long
time. High contents of the catalytic ions and acids present in the ink can cause corrosion of the support and even its
irreversible damage. Several historical documents from National and University Library (NUL) are being studied. The
samples were measured nondestructively by the in-air PIXE for determination of the iron gall elemental composition. The
measured concentrations prove that the analyzed inks contain a variety of different transition metals, which may influence
the ink’s corrosive character. For already measured documents dating from 14th to 19th century the ink and paper elemental
concentrations and their ratios to iron were studied by the statistical methods.
INTRODUCTION
EXPERIMENTAL
Iron gall ink was probably one of the most
important writing expedients in the European history.
It was in widespread use from the Middle Ages until
the 20th century due to ease of its manufacture, rich and
velvety tone and the fact that it was almost impossible
to be removed when applied. However, the harmful
effects of the ink on the supporting media (i.e. paper,
parchment) have been known for a long time [1]. High
concentrations of the catalytic ions and acids present in
the ink can cause corrosion of the support and even
its irreversible damage, especially in the case of
unfavorable storing conditions. For a better
understanding of these influences, knowledge about the
ink and paper composition is needed. On the basis of
the studies performed recently [2,3,4] an experimental
approach has been chosen and materials from the
Slovenian National Cultural Heritage were analyzed.
The pages of historical books and documents were
measured nondestructively by the in-air PIXE
technique. The measured concentrations prove that the
analyzed inks contain several transition metals, which
may influence the ink’s corrosive character. Data
obtained by the PIXE method will be used to evaluate
the relative corrosive properties of the iron gall ink’s
components as well as aid in development of suitable
conservation method [1].
At the in-air PIXE arrangement, installed at the
Jožef Stefan Institute (JSI) Tandetron accelerator, the 2
MeV proton beam passes the 8 µm thick aluminum foil
and transversed 9 mm of air before falling onto the
measured document. The selected points on the
document are irradiated with a proton dose of 10 µC
while limiting the proton current to less than 10 nA.
The beam is 0.7 mm in diameter as defined by the
pinhole carbon collimator. The Si(Li) detector is
positioned at 45o to the proton beam at the distance of
48 mm from the target. The exact placement of the
document is achieved by the automatic positioning
system that uses a laser beam and video camera for
controlling the set-up geometry in the direction of
proton beam (z direction). The adjusting system works
on the principle of object recognition, assuring that the
beam spot location on the document is determined with
precision of 10 µm. Additionally, the manipulation
table enables the precise moving of the document in
the x and y direction to reach and irradiate the selected
points on the document. For proton dose determination,
the Ar K X-ray intensity is used. The X-ray spectra are
analyzed with the GUPIX code and the elemental
compositions of the ink and paper are deduced. The
chemical elements measured ranged from Al to As,
between them the significant iron gall ink components
1
Supported in part by the European Commission, the 5th Framework
Program, Contract n°: EVK4-CT-2001-0049
CP680, Application of Accelerators in Research and Industry: 17th Int'l. Conference, edited by J. L. Duggan and I. L. Morgan
© 2003 American Institute of Physics 0-7354-0149-7/03/$20.00
436
1 .05
like Fe, S, K, Cu, Zn, Co, Mn, and Ni were deduced.
The measurements were done nondestructively and no
visible damage has been observed on the irradiated
documents.
0 .95
Fe
(d))/(C c(D c)/C c(D c))
1 .00
0 .90
i
ANALYSIS
Fe
0 .80
0 .75
(C m(d)/C
As a part of the InkCor program [1] sixty historical
documents dating from 14th to 19th century were
analyzed up to now. On each page 5 ink points and 3
paper points were selected. This way the number of
measurements was big enough for a reliable statistical
analysis of the ink and paper elemental composition.
The chemical structure of iron gall inks and papers
depends on many factors. The most important are the
raw materials and the technology available at the time.
Also, preparation of ink was strongly dependent on
individual scriptor skills and preferences, which
significantly influenced the quality of the final product
(ink).
There are several additional factors, which can
influence the analysis. The first could be the inhomogeneity of the ink elemental composition in the
inkpot. Therefore the composition of the applied ink
could depend on where in the pot the pen was
moistened. The second factor could depend upon the
manner with which the ink was applied on the paper.
The writer might have applied more ink at particular
points to emphasize some important parts of the text,
initials for example.
As the PIXE method is a surface technique, it is
necessary to take into account the thickness and profile
of the ink deposit on the paper. The proton range for
the 1.7 MeV protons in cellulose, which we have taken
as a basis for the paper, is around 100 µm. If the ink
deposit is shallower, then this information should be
taken into account at the analysis. Estimations done
showed that the accuracy of the PIXE results depends
drastically on the ink deposit thickness. In Fig. 1. the
deviations of the elemental concentration ratios from
the GUPIX values were deduced. Namely, in GUPIX
when analyzing thick targets a presumption is used that
the deposit is thicker or equal to the proton range. To
clarify this assumption the calculations were done
where the deposit thickness and ink composition were
varied and taken into account. Also the paper matrix,
basically cellulose, has been improved by inclusion of
typical paper additives, Cl for example. It came out
that the corrections are higher for light Z elements and
bigger than 20% for ink deposits shallower than 30%
of the proton range. Also, the corrections are
increasing with the density of the ink and are larger for
bigger concentrations of medium Z elements (Fe, Cu,
Zn) in the ink.
i
m
0 .85
S/Fe
K/Fe
Fe/Fe
0 .70
0.0
0.1
0.2
0.3
0 .4
0.5
0.6
0.7
0.8
0 .9
1.0
d/D c
FIGURE 1. Corrections in the concentration ratios for S/Fe
and K/Fe when ink deposit is smaller than the proton range.
The ink concentrations used (S = 20800 ppm, K = 21600
ppm, Fe = 37600 ppm) are slightly higher than the average.
The paper matrix is cellulose with addition of Cl (500 ppm).
Here, d is ink deposit thickness, Dc proton range in cellulose,
Ci and CFe are elemental concentrations (index c means pure
cellulose matrix, and m is cellulose matrix imbued with ink).
IRON GALL INK DATA BASE
The analysis of the selected documents with the
PIXE method resulted in an extensive data base which
includes the concentrations and concentration ratios for
several major and trace elements belonging to inks and
papers. Due to limitations of the in-air PIXE the
elements lighter than P were not determined. The data
base includes the observations and remarks about ink
appearance on the paper as well as about the analytical
problems encountered at the measurements.
A basic request of the whole task, the imperative
that the analysis should be done nondestructively,
places some limitations onto the analytical technique.
It has became obvious that the PIXE analysis can serve
properly only on written records which are broader
than the proton beam. In other cases the beam profile
can sense blank paper in the vicinity of the record also.
On the basis of this consideration, we believe that the
elemental concentration ratios offer more reliable
information about the composition than the measured
concentrations themselves. However, the concentration
values have enormous importance as the data for
elaborate statistical analysis.
Another important aspect of the study is that the
written records represent individual skills and
preferences applied by the scriptor. Therefore we
should expect large spreading in the measured
concentrations, not only between different writers and
periods when the document were written, but also for a
particular scriptor, even when he applied one ink type
437
selected elements are the major ingredients of the inks,
where Fe, Cu, and Zn originate from the vitriol ore,
and K mainly from the gallnuts. The concentrations
and the concentration ratios to iron are presented in
Table 1. The results include the standard deviation of
the measured values also.
on the same page. Such assumptions have been
confirmed by the analytical results. On Fig. 2. the
distributions of concentration ratios to iron for S, K,
Cu, and Zn are given. It is quite clear that in the long
period of a few centuries the compositions of the
iron gall inks had been changing drastically. The
20
40
18
35
No. of events
16
14
No. of events
12
10
30
25
20
8
15
6
10
4
2
5
0
0.0
0.5
1.0
1.5
2.0
2.5
0
3.0
0.0
S/Fe
0.2
0.4
0.6
0.8
1.0
Cu/Fe
40
14
35
12
30
25
No. of events
No. of events
10
8
6
20
15
4
10
2
5
0
0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0
1.4
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Zn/Fe
K/Fe
FIGURE 2. The distribution of concentration ratios S/Fe, K/Fe, Cu/Fe, Zn/Fe for 60 documents measured. It is interesting to see
that the distributions of S, Cu, and Zn, originating from the vitriol ores, are much narrower than the one for K, which comes from
the gallnuts. For Cu and Zn small separate peaks can be seen on the right corresponding to high concentration of these two
elements in particular inks.
TABLE 1. The values of concentrations and concentration ratios for some
measured elements
INK - 30 documents PAPER - 30 documents
INK - 60 documents
Elem. Conc. (µg/g)
Elem. Conc. (µg/g)
Conc. Ratios (Elem/Fe)
S
12600 ± 12000
2300 ± 1920
0.580 ± 0.430
Cl
197 ± 230
550 ± 630
0.042 ± 0.090
K
13500 ± 11400
1220 ± 1330
0.460 ± 0.280
Ca
4200 ± 3600
2040 ± 1330
0.660 ± 0.840
Fe
23000 ± 17600
430 ± 200
1
Cu
1070 ± 2000
60 ± 90
0.178 ± 0.250
Zn
1160 ± 1310
45 ± 96
0.176 ± 0.290
As
280 ± 880
121 ± 320
0.014 ± 0.057
438
correlation between Cu/Fe and Zn/Fe. On the contrary the
correlation between the two groups is relatively small. See
Fig. 3. The reason is that ores with higher Cu and Zn
concentrations were applied to some older documents, where
these two elements replaced part of the Fe contents.
However, if we remove the most influential data points the
remaining data show little correlation. The explanation is in
big variety of raw materials used at ink preparation. The
principal component analysis (PCA) based on the correlation
matrix confirmed above observations. The grouping of the
documents can be identified through increased Zn and Cu
concentrations, while the majority of the documents are
distributed in the group with small Zn and Cu values. Within
this group two subgroups with increased K and S
concentrations can be identified also. See Fig. 4. For blank
papers no correlation between the elements belonging to
papers can be observed. However, it is possible to see the
technology differences where grouping of the documents on
the basis of Ca, Cl, K(S), and even As can be identified.
A statistical evaluation of the measured concentrations
presents interesting findings related to the ink and paper
composition. For sixty documents studied we have found a
correlation between S/Fe and K/Fe in inks, and a better
0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
2.0
1.5
S
1.0
0.5
0.0
1.2
1.0
0.8
K
0.6
0.4
0.2
0.0
0.8
0.6
Cu
0.4
0.2
0.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Zn
CONCLUSIONS
0.0
0.5
1.0
1.5
2.0
0.0
0.2
0.4
0.6
0.8
The study of the historical documents from the
Slovenian Historical Heritage has led to an extensive
database comprising the iron gall ink and paper
elemental concentrations. It has been proved that the
in-air PIXE technique can be reliably used for
nondestructive measurements of such precious samples
as the paper documents. The data base produced can
serve for elaborate statistical studies of the applied
historical iron gall inks and papers as well as for
decisions about the methods for conservation treatment
of the endangered documents due to ink corrosion.
FIGURE 3. Correlations between S/Fe, K/Fe, Cu/Fe and
Zn/Fe for documents measured.
ACKNOWLEDGEMENTS
Authors appreciate the financial support given through
the EU 5th EU Framework Program for the Project
InkCor, Contract no : EVK4-CT-2001-0049, and
funds from the Slovenian Ministry of Education,
Science, and Sport.
REFERENCES
1.
2.
3.
FIGURE 4. The PCA analysis of sixty documents based on
the S/Fe, K/Fe, Cu/Fe, and Zn/Fe data. A group rich in Cu
and Zn can be identified for some older documents.
4.
439
Kolar, J., within references of The InkCor Kickoff Meeting, Ljubljana,, March 2002.
Lucarelli, F., Mandò, P.A., Nucl, Instr. Meth.
Phys. Res. B109/110 , 644-652 (1994).
Vodopivec, J., Budnar, M., "Analysis of Iron Gall
Ink by PIXE", Proceedings of The Iron Gall Ink
Meeting, edited by A. Jean E. Brown, University
of Northumbria at Newcastle, 2001, pp.47-52
Budnar, M., Vodopivec, J., Mandò, P.A.,
Lucarelli, F., Casu, G., Signorini, O., Restaurator
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