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X-ray fluorescence spectrometry on paper characterization: A case study on XVIII and XIX century documents
Spectrochimica Acta Part B 63 (2008) 1320–1323
Contents lists available at ScienceDirect
Spectrochimica Acta Part B j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s a b
Technical note
X-ray fluorescence spectrometry on paper characterization: A case study on XVIII and XIX century documents M. Manso, M. Costa, M.L. Carvalho ⁎ Centro de Física Atómica, Universidade de Lisboa, Faculdade de Ciências, Av. Prof. Gama Pinto 2, 1649-003 Lisboa, Portugal
a r t i c l e
i n f o
Article history: Received 31 January 2008 Accepted 13 July 2008 Available online 22 July 2008 Keywords: X-ray fluorescence spectrometry Paper characterization Elemental analysis Cultural heritage
a b s t r a c t Paper documents from XVIII and XIX centuries were analyzed by energy dispersive X-ray fluorescence. The presence of Co (400 µg g− 1), Ni (300 µg g− 1), As (2000 µg g− 1) and Bi (200 µg g− 1) in Dutch papers and a Hespe watermarked paper allowed distinguishing them from the rest of the papers. The elemental composition of the ink present in these documents was also studied with the same technique and it was concluded that these elements could not be originated from ink dissemination. Strong positive Spearman correlations between Co, Ni, As and Bi were found in all Dutch and Hespe watermarked papers. Potassium and Ca are the predominant elements in all analyzed papers. Their concentration levels also allowed differentiating between Dutch and Hespe papers and the rest of the papers. Other elements such as Ti, Fe, Cu, Zn, Ba and Pb were also found. In this work a bibliographic research about the possible origin of each one of the mentioned elements present in the papers is also reported. © 2008 Elsevier B.V. All rights reserved.
1. Introduction The methods used in paper making during the early centuries of the art are naturally vague after a lapse of over a thousand years [1]. It is thought that Chinese originated the craft of papermaking as early as 105 B.C. [2–4] and that the art was introduced into Samarkand and Bagdad in the VIII century, spreading to Europe three centuries later [1,4]: first into Spain, then Italy followed by France and the Netherlands [1–4]. Sheets of paper were made from disintegrated fiber upon flat moulds before the time of Christ and were still formed in this fashion afterwards. The only difference relied in the construction of the moulds and the treatment of the fiber. The process in principle remained the same [5,6]. Early craftsmen jealously guarded the art of papermaking and as there was little intercourse between the different mills, it was natural that papermakers had slightly differentiated methods of working [1]. Information about these differences can be achieved by elemental characterization of paper by X-ray fluorescence. This technique demonstrates possibilities for determining which elements were present in the original paper and which the papermaker added. It also can help differentiating the elements suspended or dissolved in the water processing from the ones picked up from the processing equipment or added by paper users [7–9]. In this study, we analyzed the elemental composition of paper documents from XVIII and XIX centuries by energy dispersive X-ray fluorescence technique (EDXRF). The major advantage of this technique
⁎ Corresponding author. Tel.: +351 961051293; fax: +351 217954288. E-mail address: [email protected] (M.L. Carvalho). 0584-8547/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2008.07.001
is that it is non-destructive, making it the perfect tool for elemental analysis of cultural heritage. The application of this technique allows paper elemental characterization preserving its integrity [10,11]. 2. Experimental The spectrometer used in this work for EDXRF analysis consisted of a commercial X-ray tube (PW 1140; 100 kV, 80 mA) equipped with a changeable secondary target of molybdenum (Mo). The X-ray tube, the secondary target and the sample are in a triaxial geometry [12,13]. The characteristic radiation emitted by the elements present in the sample was detected by means of a Si (Li) detector, with a 30 mm2 active area and 8 μm beryllium window. The energy resolution was 138 eV at 5.9 keV and the acquisition system was a Nucleus PCA card. The pulse processing and dead time corrections were automatically adjusted by a commercial pulse processor (Oxford). The quantitative evaluation was made by the fundamental parameters methods [14,15]. The X-ray generator was operated at 50 kV and 20 mA, and a typical acquisition time of 1000 s was used. The performances of the instrumentation with respect to the limits of detection achievable and accuracy of the results reported in a previous publication [8] were confirmed here or slightly improved, as in the case of the limits of detection. The analyzed samples consisted on paper documents dated from 1779 to 1822. Dutch watermarks were identified in documents dated from 1779, 1781, 1787 and 1817; Dirk and Cornelius Blaw watermark was recognized in documents from 1779, 1781 and 1817; Zoonen watermark was present in papers dated from 1781 and 1787. The origin of Hespe
M. Manso et al. / Spectrochimica Acta Part B 63 (2008) 1320–1323
1321
Table 1 Median values and ranges for the elemental concentrations (µg g− 1) based on N = 10 points obtained for different papers Elements
K Ca Ti Fe Co Ni Cu Zn As Ba Pb Bi
Paper manufacturer and year of production
Median Range Median Range Median Range Median Range Median Range Median Range Median Range Median Range Median Range Median Range Median Range Median Range
Dirk & Cornelius Blaw 1779
Dirk & Cornelius Blaw 1781a
Dirk & Cornelius Blaw 1817
Zoonen 1781b
Zoonen 1787
Hespe 1818
2680 2540–3200 825 670–1015
4350 4110–5720 1440 1355–1900 146 134–220 1070 1015–1185 470 460–500 280 260–285 195 190–205 108 100–115 1620 1600–1780 685 667–855 145 127–160 145 134–147
2250 1650–2310 925 850–1015
4550 4060–4740 1595 1540–1640
550 470–570 215 178–230 134 126–136 145 125–200 32 30–37 1140 1045–1210
1580 1450–1690 340 290–350 150 140–166 355 317–359 92 92–96 865 793–922 210 195–214 116 108–119 130 110–143
2060 1489–2492 1330 830–2060 84 38–122 585 440–644 300 224–356 246 200–290 250 198–262 73 55–83 1120 803–1335 395 264–520 80 65–90 136 103–168
2930 2255–3500 960 823–1235 163 127–200 855 698–956 320 254–345 300 246–320 92 77–96 28 26–29 2675 2168–2860
860 740–935 410 345–434 270 238–300 89 72–197 90 76–116 1650 1435–1760
96 80–122 245 205–262
46 41–58 107 102–120
watermark in the paper from 1818 was not identified. The remaining documents from 1781 to 1822 were not watermarked. All papers were directly measured by EDXRF, without any kind of sample preparation for elemental characterization. The ink of Dutch and Hespe documents was also analyzed. A minimum of ten measurements was undertaken for each paper sample and respective ink. 3. Results and discussion Paper is mainly made from cellulose fiber. Various compounds other than cellulose are often incorporated in the paper to impart specific properties [5]. Tables 1 and 2 show the median values and ranges for the elemental content in the analyzed papers. These elements could exist already in the raw material, or being incorporated either during the manufacturing process, or by the environment in which they were preserved. The wide ranges obtained for some elements in the same document are due to paper inhomogeneity. Potassium, Ca, Fe, Cu and Zn are present in all the analyzed papers, although at different concentration levels. Between 1400 and 1800 most stampers head were shod with Fe or bronze (copper alloys). The equipment would then contribute to
58 58–75 265 210–298
the presence of these two metals in paper [6]. Zinc occurrence has already been reported in Holland papers from 1770 as possibly coming from white zinc oxide [7]. During papermaking, cellulose fiber very rapidly accumulates dissolved metals in water. Hence the presence of Ca, Fe and Cu in paper may also be due to water contamination [6,7]. In all the studied papers the highest concentration was observed for K, Ca and Fe. These elements also present the widest concentration ranges. The high levels of Ca are not surprising since this element takes part in several steps of the papermaking process. The presence of this element could then be due to the processing water supply; hide, bones and other animal parts used in the gelatine size; slaked lime used in the fermentation process; a whitening agent added to the pulp to counteract the yellowing effect of the fermentation step [5–7]. Potassium was mostly added as alum, a sizing agent, and also as muscovite, a mineral filler [5,7]. The comparison between K and Ca concentrations in each paper is shown in Fig. 1. In this figure we can identify two groups of paper. In the first group of papers (1779, 1781a, 1781b, 1787, 1817, 1818) K values are much higher than Ca values. The opposite is true for the second group (1781c, 1782a, 1782b, 1786, 1788, 1821, 1822), where Ca levels are far
Table 2 Median values and ranges for the elemental concentrations (µg g− 1) based on N = 10 points obtained for different papers Elements
K Ca Fe Cu Zn Pb
Paper years
Median Range Median Range Median Range Median Range Median Range Median Range
1781c
1782a
1782b
1786
1788
1821
1822
1285 1080–1600 4980 4275–6450 385 306–560 26 13–31 17 12–23 49 27–66
610 493–704 6400 6285–7585 330 316–386 37 30–66 15 14–16 72 61–78
410 356–712 5390 4920–5956 220 187–235 19 18–26 11 8–14 25 20–32
885 754–1030 1510 1130–1660 250 217–325 27 19–36 13 11–19 31 25–42
325 240–475 5455 4888–6670 230 205–340 25 23–38 53 46–57
630 457–790 2720 2500–3096 318 288–360 208 170–400 26 23–54 266 234–280
365 266–459 3910 3675–4165 240 210–270 360 345–392 14 13–18 39 29–50
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M. Manso et al. / Spectrochimica Acta Part B 63 (2008) 1320–1323 Table 3 Spearman rank order correlations for the studied elements present in the papers
K Ca Fe Co Ni Cu Zn As Pb
Ca
Fe
Co
Ni
Cu
Zn
As
Pb
Bi
0.55
0.63 0.65
0.53 0.45 0.78
0.45 0.51 0.86 0.82
0.60 0.28 0.53 0.48 0.34
0.40 0.44 0.72 0.78 0.65 0.64
0.44 0.61 0.92 0.84 0.94 0.34 0.72
−0.05 0.22 0.20 0.06 0.36 −0.09 0.01 0.35
0.50 0.57 0.86 0.89 0.87 0.43 0.76 0.93 0.27
Marked correlations are significant at p b 0.01.
Fig. 1. Comparison between K and Ca concentration (µg g− 1) levels in the analyzed papers.
above K levels. From Fig. 1 we can also understand that all Dutch and Hespe papers form one group, while all the other analyzed papers belong to a different group. Some Dutch papers also showed the presence of Ti and Ba (Table 1). The presence of these elements was already reported in documents from the beginning of the XIX century [8,9]. According to Hanson [7], Ba appeared in Holland in 1770. Barium sulphate is virtually limited to paper coating but in very rare instances might be reported as filler [16]. Titanium can be used as minor filler. The refractive index of titanium dioxide is much higher than that of conventional fillers. It therefore scatters light more readily and hence has a greater opacifying power [17,18] and it is used in papers such as “Bible” paper where opacity has to be imparted to a thin sheet which would otherwise be unacceptably transparent. Since it can be prepared in a very pure state it is also a very white pigment [16] that can be used as optical bleach [18]. Lead was found in almost all the analyzed papers. This element was already found in some coated paper and board from 1890 [7]. Its presence is probably due to a coating mixture containing lead white, which was patented in 1764 as plaster of Paris [19]. Also this metal could have come from the processing equipment [7]. Very high concentrations of Co, Ni, As, and Bi were observed. These elements were found together, in very high concentration levels, for the
first time in the present study in the Dutch and Hespe paper (Table 1). The results revealed Co values from 200–500 µg g− 1, Ni 100–300 µg g− 1, As 1000–3000 µg g− 1 and Bi values from 100 to 300 µg g− 1. These four elements are found together in some minerals like smaltite (Co,Fe,Ni)As2 or Schneebergite (Bi(Co,Ni)2(AsO4)2(OH, H2O)2 ) which appear in very few regions in Europe, especially in Germany. This strong contamination might suggest that the paper mills were located near by these regions, allowing identification of the manufacturer and the origin of the paper. These elements are not commonly found in high concentrations and have never been reported together in paper composition. Some references have however been made to the individual presence of these elements, though in low concentrations, in a group of Dutch and American papers covering the period 1770 to 1900. Bismuth has been used in 1820 in white papers and papers watermarked “Law” or “Legal” made by Thomas Amies of Philadelphia [7]. Arsenic has been detected together with Co in Amies papers as an impurity in smalt [3,7]. Nickel appeared also in Holland-made papers and in the pink Amies' papers [7]. The elemental content of the ink present in Dutch and Hespe papers was also studied in order to check the possibility of these elements having been originated from the ink. The elemental content of the ink of each paper was measured and compared with the obtained results for paper region. In Fig. 2 we present the results obtained for Dutch paper from 1779. From this figure we can observe that the elemental content of Co, Ni, As and Bi measured in the ink region and in the paper region is of the same order of magnitude. The same results were obtained for the other analyzed papers. These data allow concluding that these four elements are not present in the paper due to ink dissemination. From Fig. 2 we can also observe that the only significant differences were for Fe, Cu, Zn and Hg. These elements present higher concentration in the ink region than in the paper region; hence the ink present in Dutch paper from 1779 should have Fe, Cu, Zn and Hg in its composition guarantying that Co, Ni, As and Bi belong to paper composition. The Spearman correlation coefficients test, rs, was applied to study the elemental concentration of papers from Table 1. According to this test, the closer |rs| values are to 1, the stronger is the correlation, for a significance p = 0.01. The p-level represents the probability of error that is involved in accepting our observed result as valid. All papers from Table 3 presented strong positive correlations between the concentration level of Fe–Co, Fe–Ni, Co–Ni, Zn–Ni, As–Fe, As–Co, As–Ni, As–Zn, Bi– Fe, Bi–Co, Bi–Ni, Bi–Zn and Bi–As. The correlation values in common are highlighted in italic bold for Dirk and Cornelius Blaw paper from 1779 in Table 3. The strong correlation coefficients between Co–Ni, As–Co, As– Ni, Bi–Co, Bi–Ni and Bi–As corroborate the use of a mineral with these four elements in its composition. 4. Conclusion
Fig. 2. Comparison between the mean elemental concentration (µg g− 1) for paper and ink regions from one of the documents of Dirk and Cornelius Blaw (1779). The error bar is the standard deviation of the concentration for the several analyzed points.
This work highlights the presence of Co, Ni, As and Bi in paper composition, allowing easy identification of the manufacturer. These four elements have never been reported together in paper in such high concentrations. This statement, together with the strong correlation
M. Manso et al. / Spectrochimica Acta Part B 63 (2008) 1320–1323
coefficients between the same elements, suggests the use of a mineral containing these four elements in paper composition. It is believed that the results obtained in this work will contribute to a data base on paper elemental characterization in order to provide efficient paper identification. As a final remark, this work emphasizes again the application of Xray fluorescence in identification and characterization of different kinds of paper. Being non-destructive is an essential feature of this technique in the analysis of ancient documents with historical value. References [1] D. Hunter, Old Papermaking, 1923. [2] T. Collings, D. Milner, Pap. Conserv. 14 (1990) 58–61. [3] B. Rudin, R.G. Tanner, Making Paper: A Look into the History of an Ancient Craft, Lyons Press, Sweden, 1990 Vallingby: Rudins. [4] E. Piedmonte, E. Princi, S. Vicini, Storia della produzione della carta, La Chimica e l'Industria, vol. 8, 2005, pp. 62–87. [5] K. Beazley, Mineral fillers in paper, Pap. Conserv. 15 (1991) 17–27. [6] P. Reynard, Early European papermaking methods 1400–1800, Pap. Conserv.13 (1989) 7–27. [7] V.F. Hanson, Determination of the trace elements in paper by Energy Dispersive X-ray Fluorescence, in: J.C. Williams (Ed.), Advances in Chemistry Series, American Chemical Society, Washington, D.C., 1981, pp. 53–78. [8] M. Manso, M.L. Carvalho, Elemental identification of document paper by X-ray fluorescence spectrometry, J. Anal. At. Spectrom. 22 (2007) 164–170.
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[9] M. Manso, M. Costa, M.L. Carvalho, Comparison of elemental content on modern and ancient papers by EDXRF, Appl. Phys. A 90 (2008) 43–48. [10] J.L. Ferrero, C. Roldán, D. Juanes, J. Carballo, J. Pereira, M. Ardid, J.L. Lluch, R. Vives, Study of inks on paper engravings using portable EDXRF spectrometry, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, vol. 213, 2004, pp. 729–734. [11] M. Mantler, M. Schreiner, X-ray fluorescence in art and archaeology, X-ray Spectrom. 29 (2000) 3–17. [12] T. Magalhães, A. von Bohlen, M.L. Carvalho, M. Becker, Trace elements in human cancerous and healthy tissues from the same individual: a comparative study by TXRF and EDXRF, Spectrochim. Acta Part B 61 (2006) 1185–1193. [13] J. Boman, E. Selin, M. Öblad, Time and position dependent artifacts in X-ray spectra from a Si(Li) detector, Phys. Scr. 37 (1988) 274–278. [14] A. Rindby, Software for energy-dispersive X-ray fluorescence, X-ray Spectrom. 18 (1989) 113–118. [15] J. Bohman, J. Isakson, Comparison between two X-ray analysis software packages, X-ray Spectrom. 20 (1991) 305–314. [16] W.R. Willets, The opacifying of paper by means of titanium pigments, Technical Association Papers, vol. 17, 1934, pp. 423–426. [17] W.R. Willets, Titanium pigments in printing papers, Paper mill and wood pulp news, vol. 58, 1935, pp. 15–18. [18] M. Rožić, M. Rožmarić Mačefat, V. Oreščanin, Elemental analysis of ashes of office papers by EDXRF spectrometry, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, vol. 229, 2005, pp. 117–122. [19] D. Hunter, Papermaking, Dover Publications, New York, 1978.
Contents lists available at ScienceDirect
Spectrochimica Acta Part B j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s a b
Technical note
X-ray fluorescence spectrometry on paper characterization: A case study on XVIII and XIX century documents M. Manso, M. Costa, M.L. Carvalho ⁎ Centro de Física Atómica, Universidade de Lisboa, Faculdade de Ciências, Av. Prof. Gama Pinto 2, 1649-003 Lisboa, Portugal
a r t i c l e
i n f o
Article history: Received 31 January 2008 Accepted 13 July 2008 Available online 22 July 2008 Keywords: X-ray fluorescence spectrometry Paper characterization Elemental analysis Cultural heritage
a b s t r a c t Paper documents from XVIII and XIX centuries were analyzed by energy dispersive X-ray fluorescence. The presence of Co (400 µg g− 1), Ni (300 µg g− 1), As (2000 µg g− 1) and Bi (200 µg g− 1) in Dutch papers and a Hespe watermarked paper allowed distinguishing them from the rest of the papers. The elemental composition of the ink present in these documents was also studied with the same technique and it was concluded that these elements could not be originated from ink dissemination. Strong positive Spearman correlations between Co, Ni, As and Bi were found in all Dutch and Hespe watermarked papers. Potassium and Ca are the predominant elements in all analyzed papers. Their concentration levels also allowed differentiating between Dutch and Hespe papers and the rest of the papers. Other elements such as Ti, Fe, Cu, Zn, Ba and Pb were also found. In this work a bibliographic research about the possible origin of each one of the mentioned elements present in the papers is also reported. © 2008 Elsevier B.V. All rights reserved.
1. Introduction The methods used in paper making during the early centuries of the art are naturally vague after a lapse of over a thousand years [1]. It is thought that Chinese originated the craft of papermaking as early as 105 B.C. [2–4] and that the art was introduced into Samarkand and Bagdad in the VIII century, spreading to Europe three centuries later [1,4]: first into Spain, then Italy followed by France and the Netherlands [1–4]. Sheets of paper were made from disintegrated fiber upon flat moulds before the time of Christ and were still formed in this fashion afterwards. The only difference relied in the construction of the moulds and the treatment of the fiber. The process in principle remained the same [5,6]. Early craftsmen jealously guarded the art of papermaking and as there was little intercourse between the different mills, it was natural that papermakers had slightly differentiated methods of working [1]. Information about these differences can be achieved by elemental characterization of paper by X-ray fluorescence. This technique demonstrates possibilities for determining which elements were present in the original paper and which the papermaker added. It also can help differentiating the elements suspended or dissolved in the water processing from the ones picked up from the processing equipment or added by paper users [7–9]. In this study, we analyzed the elemental composition of paper documents from XVIII and XIX centuries by energy dispersive X-ray fluorescence technique (EDXRF). The major advantage of this technique
⁎ Corresponding author. Tel.: +351 961051293; fax: +351 217954288. E-mail address: [email protected] (M.L. Carvalho). 0584-8547/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2008.07.001
is that it is non-destructive, making it the perfect tool for elemental analysis of cultural heritage. The application of this technique allows paper elemental characterization preserving its integrity [10,11]. 2. Experimental The spectrometer used in this work for EDXRF analysis consisted of a commercial X-ray tube (PW 1140; 100 kV, 80 mA) equipped with a changeable secondary target of molybdenum (Mo). The X-ray tube, the secondary target and the sample are in a triaxial geometry [12,13]. The characteristic radiation emitted by the elements present in the sample was detected by means of a Si (Li) detector, with a 30 mm2 active area and 8 μm beryllium window. The energy resolution was 138 eV at 5.9 keV and the acquisition system was a Nucleus PCA card. The pulse processing and dead time corrections were automatically adjusted by a commercial pulse processor (Oxford). The quantitative evaluation was made by the fundamental parameters methods [14,15]. The X-ray generator was operated at 50 kV and 20 mA, and a typical acquisition time of 1000 s was used. The performances of the instrumentation with respect to the limits of detection achievable and accuracy of the results reported in a previous publication [8] were confirmed here or slightly improved, as in the case of the limits of detection. The analyzed samples consisted on paper documents dated from 1779 to 1822. Dutch watermarks were identified in documents dated from 1779, 1781, 1787 and 1817; Dirk and Cornelius Blaw watermark was recognized in documents from 1779, 1781 and 1817; Zoonen watermark was present in papers dated from 1781 and 1787. The origin of Hespe
M. Manso et al. / Spectrochimica Acta Part B 63 (2008) 1320–1323
1321
Table 1 Median values and ranges for the elemental concentrations (µg g− 1) based on N = 10 points obtained for different papers Elements
K Ca Ti Fe Co Ni Cu Zn As Ba Pb Bi
Paper manufacturer and year of production
Median Range Median Range Median Range Median Range Median Range Median Range Median Range Median Range Median Range Median Range Median Range Median Range
Dirk & Cornelius Blaw 1779
Dirk & Cornelius Blaw 1781a
Dirk & Cornelius Blaw 1817
Zoonen 1781b
Zoonen 1787
Hespe 1818
2680 2540–3200 825 670–1015
4350 4110–5720 1440 1355–1900 146 134–220 1070 1015–1185 470 460–500 280 260–285 195 190–205 108 100–115 1620 1600–1780 685 667–855 145 127–160 145 134–147
2250 1650–2310 925 850–1015
4550 4060–4740 1595 1540–1640
550 470–570 215 178–230 134 126–136 145 125–200 32 30–37 1140 1045–1210
1580 1450–1690 340 290–350 150 140–166 355 317–359 92 92–96 865 793–922 210 195–214 116 108–119 130 110–143
2060 1489–2492 1330 830–2060 84 38–122 585 440–644 300 224–356 246 200–290 250 198–262 73 55–83 1120 803–1335 395 264–520 80 65–90 136 103–168
2930 2255–3500 960 823–1235 163 127–200 855 698–956 320 254–345 300 246–320 92 77–96 28 26–29 2675 2168–2860
860 740–935 410 345–434 270 238–300 89 72–197 90 76–116 1650 1435–1760
96 80–122 245 205–262
46 41–58 107 102–120
watermark in the paper from 1818 was not identified. The remaining documents from 1781 to 1822 were not watermarked. All papers were directly measured by EDXRF, without any kind of sample preparation for elemental characterization. The ink of Dutch and Hespe documents was also analyzed. A minimum of ten measurements was undertaken for each paper sample and respective ink. 3. Results and discussion Paper is mainly made from cellulose fiber. Various compounds other than cellulose are often incorporated in the paper to impart specific properties [5]. Tables 1 and 2 show the median values and ranges for the elemental content in the analyzed papers. These elements could exist already in the raw material, or being incorporated either during the manufacturing process, or by the environment in which they were preserved. The wide ranges obtained for some elements in the same document are due to paper inhomogeneity. Potassium, Ca, Fe, Cu and Zn are present in all the analyzed papers, although at different concentration levels. Between 1400 and 1800 most stampers head were shod with Fe or bronze (copper alloys). The equipment would then contribute to
58 58–75 265 210–298
the presence of these two metals in paper [6]. Zinc occurrence has already been reported in Holland papers from 1770 as possibly coming from white zinc oxide [7]. During papermaking, cellulose fiber very rapidly accumulates dissolved metals in water. Hence the presence of Ca, Fe and Cu in paper may also be due to water contamination [6,7]. In all the studied papers the highest concentration was observed for K, Ca and Fe. These elements also present the widest concentration ranges. The high levels of Ca are not surprising since this element takes part in several steps of the papermaking process. The presence of this element could then be due to the processing water supply; hide, bones and other animal parts used in the gelatine size; slaked lime used in the fermentation process; a whitening agent added to the pulp to counteract the yellowing effect of the fermentation step [5–7]. Potassium was mostly added as alum, a sizing agent, and also as muscovite, a mineral filler [5,7]. The comparison between K and Ca concentrations in each paper is shown in Fig. 1. In this figure we can identify two groups of paper. In the first group of papers (1779, 1781a, 1781b, 1787, 1817, 1818) K values are much higher than Ca values. The opposite is true for the second group (1781c, 1782a, 1782b, 1786, 1788, 1821, 1822), where Ca levels are far
Table 2 Median values and ranges for the elemental concentrations (µg g− 1) based on N = 10 points obtained for different papers Elements
K Ca Fe Cu Zn Pb
Paper years
Median Range Median Range Median Range Median Range Median Range Median Range
1781c
1782a
1782b
1786
1788
1821
1822
1285 1080–1600 4980 4275–6450 385 306–560 26 13–31 17 12–23 49 27–66
610 493–704 6400 6285–7585 330 316–386 37 30–66 15 14–16 72 61–78
410 356–712 5390 4920–5956 220 187–235 19 18–26 11 8–14 25 20–32
885 754–1030 1510 1130–1660 250 217–325 27 19–36 13 11–19 31 25–42
325 240–475 5455 4888–6670 230 205–340 25 23–38 53 46–57
630 457–790 2720 2500–3096 318 288–360 208 170–400 26 23–54 266 234–280
365 266–459 3910 3675–4165 240 210–270 360 345–392 14 13–18 39 29–50
1322
M. Manso et al. / Spectrochimica Acta Part B 63 (2008) 1320–1323 Table 3 Spearman rank order correlations for the studied elements present in the papers
K Ca Fe Co Ni Cu Zn As Pb
Ca
Fe
Co
Ni
Cu
Zn
As
Pb
Bi
0.55
0.63 0.65
0.53 0.45 0.78
0.45 0.51 0.86 0.82
0.60 0.28 0.53 0.48 0.34
0.40 0.44 0.72 0.78 0.65 0.64
0.44 0.61 0.92 0.84 0.94 0.34 0.72
−0.05 0.22 0.20 0.06 0.36 −0.09 0.01 0.35
0.50 0.57 0.86 0.89 0.87 0.43 0.76 0.93 0.27
Marked correlations are significant at p b 0.01.
Fig. 1. Comparison between K and Ca concentration (µg g− 1) levels in the analyzed papers.
above K levels. From Fig. 1 we can also understand that all Dutch and Hespe papers form one group, while all the other analyzed papers belong to a different group. Some Dutch papers also showed the presence of Ti and Ba (Table 1). The presence of these elements was already reported in documents from the beginning of the XIX century [8,9]. According to Hanson [7], Ba appeared in Holland in 1770. Barium sulphate is virtually limited to paper coating but in very rare instances might be reported as filler [16]. Titanium can be used as minor filler. The refractive index of titanium dioxide is much higher than that of conventional fillers. It therefore scatters light more readily and hence has a greater opacifying power [17,18] and it is used in papers such as “Bible” paper where opacity has to be imparted to a thin sheet which would otherwise be unacceptably transparent. Since it can be prepared in a very pure state it is also a very white pigment [16] that can be used as optical bleach [18]. Lead was found in almost all the analyzed papers. This element was already found in some coated paper and board from 1890 [7]. Its presence is probably due to a coating mixture containing lead white, which was patented in 1764 as plaster of Paris [19]. Also this metal could have come from the processing equipment [7]. Very high concentrations of Co, Ni, As, and Bi were observed. These elements were found together, in very high concentration levels, for the
first time in the present study in the Dutch and Hespe paper (Table 1). The results revealed Co values from 200–500 µg g− 1, Ni 100–300 µg g− 1, As 1000–3000 µg g− 1 and Bi values from 100 to 300 µg g− 1. These four elements are found together in some minerals like smaltite (Co,Fe,Ni)As2 or Schneebergite (Bi(Co,Ni)2(AsO4)2(OH, H2O)2 ) which appear in very few regions in Europe, especially in Germany. This strong contamination might suggest that the paper mills were located near by these regions, allowing identification of the manufacturer and the origin of the paper. These elements are not commonly found in high concentrations and have never been reported together in paper composition. Some references have however been made to the individual presence of these elements, though in low concentrations, in a group of Dutch and American papers covering the period 1770 to 1900. Bismuth has been used in 1820 in white papers and papers watermarked “Law” or “Legal” made by Thomas Amies of Philadelphia [7]. Arsenic has been detected together with Co in Amies papers as an impurity in smalt [3,7]. Nickel appeared also in Holland-made papers and in the pink Amies' papers [7]. The elemental content of the ink present in Dutch and Hespe papers was also studied in order to check the possibility of these elements having been originated from the ink. The elemental content of the ink of each paper was measured and compared with the obtained results for paper region. In Fig. 2 we present the results obtained for Dutch paper from 1779. From this figure we can observe that the elemental content of Co, Ni, As and Bi measured in the ink region and in the paper region is of the same order of magnitude. The same results were obtained for the other analyzed papers. These data allow concluding that these four elements are not present in the paper due to ink dissemination. From Fig. 2 we can also observe that the only significant differences were for Fe, Cu, Zn and Hg. These elements present higher concentration in the ink region than in the paper region; hence the ink present in Dutch paper from 1779 should have Fe, Cu, Zn and Hg in its composition guarantying that Co, Ni, As and Bi belong to paper composition. The Spearman correlation coefficients test, rs, was applied to study the elemental concentration of papers from Table 1. According to this test, the closer |rs| values are to 1, the stronger is the correlation, for a significance p = 0.01. The p-level represents the probability of error that is involved in accepting our observed result as valid. All papers from Table 3 presented strong positive correlations between the concentration level of Fe–Co, Fe–Ni, Co–Ni, Zn–Ni, As–Fe, As–Co, As–Ni, As–Zn, Bi– Fe, Bi–Co, Bi–Ni, Bi–Zn and Bi–As. The correlation values in common are highlighted in italic bold for Dirk and Cornelius Blaw paper from 1779 in Table 3. The strong correlation coefficients between Co–Ni, As–Co, As– Ni, Bi–Co, Bi–Ni and Bi–As corroborate the use of a mineral with these four elements in its composition. 4. Conclusion
Fig. 2. Comparison between the mean elemental concentration (µg g− 1) for paper and ink regions from one of the documents of Dirk and Cornelius Blaw (1779). The error bar is the standard deviation of the concentration for the several analyzed points.
This work highlights the presence of Co, Ni, As and Bi in paper composition, allowing easy identification of the manufacturer. These four elements have never been reported together in paper in such high concentrations. This statement, together with the strong correlation
M. Manso et al. / Spectrochimica Acta Part B 63 (2008) 1320–1323
coefficients between the same elements, suggests the use of a mineral containing these four elements in paper composition. It is believed that the results obtained in this work will contribute to a data base on paper elemental characterization in order to provide efficient paper identification. As a final remark, this work emphasizes again the application of Xray fluorescence in identification and characterization of different kinds of paper. Being non-destructive is an essential feature of this technique in the analysis of ancient documents with historical value. References [1] D. Hunter, Old Papermaking, 1923. [2] T. Collings, D. Milner, Pap. Conserv. 14 (1990) 58–61. [3] B. Rudin, R.G. Tanner, Making Paper: A Look into the History of an Ancient Craft, Lyons Press, Sweden, 1990 Vallingby: Rudins. [4] E. Piedmonte, E. Princi, S. Vicini, Storia della produzione della carta, La Chimica e l'Industria, vol. 8, 2005, pp. 62–87. [5] K. Beazley, Mineral fillers in paper, Pap. Conserv. 15 (1991) 17–27. [6] P. Reynard, Early European papermaking methods 1400–1800, Pap. Conserv.13 (1989) 7–27. [7] V.F. Hanson, Determination of the trace elements in paper by Energy Dispersive X-ray Fluorescence, in: J.C. Williams (Ed.), Advances in Chemistry Series, American Chemical Society, Washington, D.C., 1981, pp. 53–78. [8] M. Manso, M.L. Carvalho, Elemental identification of document paper by X-ray fluorescence spectrometry, J. Anal. At. Spectrom. 22 (2007) 164–170.
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