Πάπυροι - Επιστημονικό Περιοδικό τόμος 3, 2014

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1 IOANNIS KARAPANAGIOTIS and KONSTANTINOS PALAVATSIOS University Ecclesiastical Academy of Thessaloniki, Department of Management and Conservation of Ecclesiastical Cultural Heritage Objects, Thessaloniki Hellas Θεσσαλονίκη 2014 Thessaloniki 2014

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3 IOANNIS KARAPANAGIOTIS and KONSTANTINOS PALAVATSIOS 1. Introduction The use of physicochemical scientific methods in the study and conservation of objects of the cultural heritage has notably expanded in recent decades [1]. We present herein a study where X-ray fluorescence (XRF) spectroscopy is used for the identification of illumination materials, including inks, which have been used on paper in the past. Historical manuscripts are objects of great importance because they include ancient texts which are extremely useful to study the history of mankind. The investigation of historical manuscripts using physicochemical approaches is a challenging task. While samples can be removed from textiles (and other large scale objects) with relatively little impact on the integrity of the object, the removal of even tiny samples from manuscripts and books is practically prohibited, because of the small scale of these objects. Consequently, the study of manuscripts is limited to non-invasive methods, such as imaging and spectroscopic techniques [2], thus increasing the degree of difficulty, for scientific investigations, dramatically. Imaging techniques can provide some very useful information regarding the condition and the degree of degradation of an artwork. However, the unequivocal identification of the materials is usually achieved using spectroscopic techniques with enhanced analytical capabilities. Several noninvasive spectroscopic techniques have been employed to characterize materials in historical manuscripts and books including, for instance, IR and Raman spectroscopies [3-7], proton-induced X-ray emission (PIXE) [8-12] and X-ray fluorescence (XRF) spectroscopy [2, 6, 13-18]. As thousands of manuscripts are spread around the world in various museums, libraries and private collections the development of handled XRF spectrometers [19,20], which provide the opportunity to study the objects on site, was a big step towards the application of the method on the investigation of manuscript collections. XRF provides elemental compositions. Consequently, decorative metals, such as gold and silver (and their impurities) used in ancient books frequently, can be directly identified with XRF. However, colouring materials such as pigments which were used in manuscript illustrations, decorative-first letters and drawings, can be identified indirectly, by detecting signature elements. Some elements that are often detected with XRF in manuscripts and used as markers for the identification of pigments are included in Table 1. It is noteworthy, that compounds described in Table 1 are commonly reported as colouring materials of paintings, icons and other artworks e.g. [21]. Except for decorative metals and pigments, XRF is also useful to record the elemental composition of paper which is a usual substrate material for written manuscripts. Measurements on paper can provide important information regarding the paper production technology and how this was developed through the years. Within this 23

4 spirit, Barrett et al. monitored the calcium concentration on 1578 handmade European paper specimens dated from around 1300 to 1900 and correlated their findings with the geographical and historical provenance of the objects [18]. Furthermore, XRF is very useful to study iron gall inks, commonly encountered in manuscripts. Another type of ink used in the past was produced from the soot generated by the combustion of organic materials. These are the carbon-based inks, which cannot be investigated with XRF because carbon, as well as other light elements, cannot be detected with this technique. Similarly, XRF is not useful to study natural organic colourants except for Tyrian purple [22], as this particular dye contains bromine (Br) which is a signature element. Iron gall inks, however, which are iron-tannin complexes can be identified with XRF, as iron (Fe), provides an excellent and distinctive XRF signal. Other elements that can be found in iron gall inks such as for instance sulphur (S), originated from the iron sulphate minerals, used as sources of Fe, and other metal ingredients are detected by XRF. In summary, the two major advantages of the XRF technique (non-invasive and portable technique) combined with its moderate/low cost of purchase/maintenance, made XRF the most frequently employed method to investigate materials in ancient manuscripts. A case study that demonstrates the identification of iron gall inks and pigments in historical manuscripts using XRF is described in the following. 2. Experimental Figure 1. Examples of manuscripts included in the study (Monastery of Dochiariou, Mount Athos, Greece) Fourteen manuscripts (18th - 19th c.) that belong to the Monastery of Dochiariou (Mount Athos, Greece) were studied. XRF measurements were carried out on site, at the library of the Monastery. The inks of the objects used for writing are mainly black, with the exception of some first letters and headings which are red. Furthermore, green decorations around the writings are present in some manuscripts and these were also included in the XRF study. Examples of the investigated objects are shown in Figure 1. A handheld X-ray fluorescence (XRF) spectrometer (Τracer IV-SD, Bruker) was used. Measurements were carried out on several areas, of the fourteen manuscripts, including written areas of black ink, red and green pigments. XRF spectra from unwritten and undecorated (blank) areas were collected to provide a background reference. These measurements, on the blank paper, were taken as a reference point to subtract any effect of the paper substrate on the investigated inks and pigments. Figure 2 shows indicative areas of manuscripts where XRF measurements were carried out. A piece of paper with a rhombus opening is used to locate the studied areas. Figure 2. Red pigment (left) and black ink (right) analysed using XRF. 24

5 3. Results and discussion Figures 3, 4 and 5 show XRF spectra collected for the black ink, red and green pigments, respectively. Measurements taken from nearby areas of blank, unwritten/undecorated paper are included in the figures to provide a reference background S Si Cl Ar K Ca Fe(Kα) Fe(Kβ) kev - Figure 3. XRF spectra of black ink (red line) and unwritten paper (green line). According to Figure 3, elevated concentrations of iron (Fe) and sulphur (S) were measured in the black ink, compared to the unwritten paper. This result suggests clearly the use of iron gall ink for writing. Significant amounts of chloride (Cl) were recorded in both written and unwritten paper. Mount Athos is a peninsula, surrounded by the Aegean sea and therefore the presence of Cl in objects from the Holy Mountain should be expected. Argon (Ar) of the atmosphere is another element reported in both spectra of written and unwritten paper of Figure 3. Furthermore, other elements found in both written and unwritten areas are potassium (K) and calcium (Ca). Finally, a small amount of silicon (Si) was recorded in the spectrum of ink, as shown in Figure 3. Results similar to those shown in Figure 3 were collected from several different areas of the fourteen manuscripts, written with black ink. Consequently, the spectrum shown in Figure 3 should be considered as a typical example, which reveals the composition of the black inks used in the fourteen investigated manuscripts. However, in two manuscripts, copper (Cu) and zinc (Zn) were detected, along with Fe, S and the other elements included in Figure 3. This finding is in agreement with previous XRF investigations which reported the occasional presence of Cu and Zn in iron gall inks [15,23,24]. Vitriol, the main inorganic compound of iron gall inks, was obtained from different mines and using various techniques [15]. Therefore, iron sulphate used in the past was sometimes contaminated with metals which are revealed by XRF [15]. Figure 4 shows a typical XRF spectrum collected for red ink. The reference spectrum of the unwritten paper is included. Significant amounts of mercury (Hg) and sulphur (S) suggest the use of cinnabar, according to Table 1. As shown in Figure 4, Hg was detected only in the red pigment and not in the unwritten paper. A large difference in the relative amounts of S detected in red pigment and unwritten paper is clearly visible in Figure 4. Consequently, both Hg and most of the detected amount of S are originated from the ink and not from the paper substrate. This result offers support to the unequivocal identification of HgS as being kev - the red ink used in the object. Interestingly, elevated concentration of Ca was recorded in the red pigment, compared to the unwritten paper, thus suggesting that this element was some S Si Cl Ar Κ Ca(Kα) Ca(Kβ) Fe Cu Hg(Lα) Hg(Lβ) Figure 4. XRF spectra of red pigment (red line) and unwritten paper (green line) 25

6 how involved in the production process of the red pigment. Furthermore a small amount of copper (Cu) was detected in the red material. Finally, other elements reported in Figure 4 such as Si, Cl, Ar, K, and Fe were discussed above (Figure 3). Finally, the green pigment, used in some manuscripts, is characterised by the elevated concentration of Cu as shown in Figure 5. This is indicative for the use of malachite (Table 1), a green pigment that has been used since antiquity. Furthermore, Ca is detected in the green pigment in high amount (Figure 5) as it was found in the red pigment (Figure 4). Other elements reported in Figure 5 such as Si, S, Cl, Ar, K and Fe were previously discussed in Figure 3. Figure 5. XRF spectra of green pigment (red line) and unwritten paper (green line). Elements detected by XRF Hg, S Pb Cu Fe As, S Pigment and chemical formula Cinnabar, HgS Lead white, 2PbCO3 Pb(OH)2 Azurite, 2CuCO3 Cu(OH)2 Malachite, CuCO3 Cu(OH)2 Haematite, Fe2O3 Yellow ochre, FeOOH Orpiment, As2S3 Table 1. Elements which are commonly detected with XRF in manuscript illuminations and used as markers for the identification of the corresponding pigments. 4. Conclusions Fourteen manuscripts (18th - 19th c., Monastery of Dochiariou, Mount Athos) were investigated using a portable X-ray fluorescence spectrometer. The relative compositions of black ink, red and green pigments were measured. XRF spectra from unwritten and undecorated (blank) areas were collected to provide a background reference. Typical results from this study are presented in Figures 3, 4 and 5 and show that iron gall ink was used for writing (Figure 3). Red and green were induced using cinnabar (Figure 4) and malachite (Figure 5), respectively Acknowledgements The authors would like to thank the Monastery of Dochiariou for providing permission to study the manuscripts. Assistance by N. Mantzouris in handling the objects is gratefully acknowledged. 26

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