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Identification of ancient textile fibres from Khirbet Qumran caves using synchrotron radiation microbeam diffraction
Spectrochimica Acta Part B 59 (2004) 1669 – 1674 www.elsevier.com/locate/sab
Identification of ancient textile fibres from Khirbet Qumran caves using synchrotron radiation microbeam diffractionB Martin Mqllera,*, Bridget Murphya, Manfred Burghammerb, Christian Riekelb, Mark Robertsc, Miroslav Papizc, David Clarkec, Jan Gunnewegd, Emmanuel Pantosc a
Institut fu¨r Experimentelle und Angewandte Physik der Christian, Albrechts, Universita¨t zu Kiel, Leibnizstr. 19, D-24098 Kiel, Germany b European Synchrotron Radiation Facility, B.P. 220, F-38043 Grenoble Cedex, France c Daresbury Laboratory, Keckwick Lane, Warrington WA4 4AD, UK d Institute of Archaeology, The Hebrew University of Jerusalem, Mount Scopus, Jerusalem, Israel Received 1 November 2003; accepted 26 February 2004 Available online 1 September 2004
Abstract Archaeological textiles fragments from the caves of Qumran in the Dead Sea region were investigated by means of X-ray microbeam diffraction on single fibres. This non-destructive technique made the identification of the used plant textile fibres possible. Apart from bast fibres (mainly flax), cotton was identified which was most unexpected in the archaeological context. D 2004 Elsevier B.V. All rights reserved. Keywords: X-ray diffraction; Synchrotron radiation; Microbeam; Archaeometry
1. Introduction The famous Dead Sea Scrolls were found in the caves of Qumran in 1947. The aim of an extended study on textiles found in Qumran is to find out the type of fibres and relate this information to the archaeological questions surrounding the mysterious Essenes, members of an eclectic religious sect, who are reported to have lived there 2100 years ago. This identification of fibre type is important since some authors suggest that the textile fragments are not from the time before 68 AD when the site of Qumran was destroyed. The information on the textiles will also allow conclusions on the trade of the Essenes in the historical context of the Dead Sea region. B This paper was presented at the International Congress on X-Ray Optics and Microanalysis (ICXOM XVII), held in Chamonix, Mont Blanc, France, 22–26 September 2003, and is published in the special issue of Spectrochimica Acta Part B, dedicated to that conference. * Corresponding author. Tel.: +49 431 880 3860; fax: +49 431 880 1685. E-mail address: [email protected] (M. Mqller).
0584-8547/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2004.07.018
The classical approach to analyse textiles is via optical and electron microscopy. Optical microscopy readily reveals the handedness of spun yarns. The shape of fibres allows for the discrimination between animal and plant fibres. Some characteristics of particular fibre types are also optically visible with the help of polarised light. The next step is a shape investigation in more detail using scanning electron microscopy (SEM) images. The microscopic techniques mentioned above were applied to textile samples from the Qumran sites [1,2], identifying wool and plant fibres like flax and cotton. However, some open questions remained, particularly concerning the plant fibres. The intact textile samples were thus investigated using synchrotron radiation X-ray diffraction with a beam of 0.2 mm in diameter [2]. The non-destructive experiments yielded diffraction diagrams, in which sharp and intense powder diffraction rings were observed. These dominating features stem from the fine mineral particles of the soil adhering to the fibres. The fibre diffraction diagrams of the small cellulose crystallites (typically 4–7 nm in diameter), so-called microfibrils, are
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difficult to resolve because of their diffuse character (small crystallites) and the non-ideal fibre orientation in the spun yarns and woven tissues. Quantitative analysis of the highly complicated resulting diffraction patterns is impossible. The recently established technique of X-ray microbeam diffraction [3] overcomes these difficulties by providing a high spatial resolution of a few Am. A focused synchrotron radiation X-ray beam with a high flux density can be used to collect diffraction diagrams of single fibres of a weakly scattering material like cellulose within a few seconds [4–6]. The aim of this article is to demonstrate the power of the advanced technique of X-ray microbeam fibre diffraction for the precise identification of single archaeological textile plant fibres.
2. Experimental For the present study, four textile fragments made from plant fibres were chosen. The selection was made in order to highlight the strengths of X-ray microbeam diffraction. They were found in different caves of the Qumran site. The numbering corresponds to Refs. [1,2] where the classical analysis (in the sense of the introduction) is reported in detail. Photographs of the samples are shown in Fig. 1. QUM 510 (Fig. 1a) is a heavily soiled fragment of a linen textile, the yarn is spun left-handed; two threads are dyed blue (visible as dark in the black and white
photograph). QUM 525 (Fig. 1b) is very probably cotton, spun right-handed. The fragment QUM 512 (Fig. 1c) is made from left-handed spun plant fibres of unidentified type. QUM 502 (Fig. 1d) represents unprocessed plant material. Fig. 2 shows the corresponding SEM images of the above samples that, together with optical microscopy [1], led to the preliminary fibre identification as stated above. Single fibres of 3–6 mm in length were carefully extracted from the samples. Compared to modern plant fibres, the archaeological fibres were extremely brittle, indicating some degradation of the material. The individual fibres with diameters between 10 and 20 Am were glued to a sample holder (metal frame), which was mounted on a goniometer head and optically aligned with the help of a video microscope. Diffraction patterns were collected at the Microfocus Beamline ID13 at the European Synchrotron Radiation Facility (ESRF, Grenoble, France). Details of the scanning diffraction set-up at ID13 may be found in a recent review [3]. X-rays of 0.096 nm wavelength were used in the experiment. The synchrotron radiation was focused to a spot size of 2 Am using an ellipsoidal mirror and a tapered glass capillary. The sample holder was scanned through the microbeam with an accuracy better than 1 Am. In an automated scan all single fibre samples were subsequently scanned in 20 steps of 3 Am. Acquisition time was 30 s per step. Two-dimensional diffraction patterns were recorded on a MAR CCD detector with 64.4564.45 Am2 pixel size. The sample-detector distance
Fig. 1. Photographs of the four textile fragments from the Qumran site. (a) QUM 510, (b) QUM 525, (c) QUM 512, (d) QUM 502.
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Fig. 2. SEM images of fibres from the textile samples. The scale bar is 100 Am in (a) and (c), 50 Am in (b) and (d). (a) QUM 510, (b) QUM 525, (c) QUM 512, (d) QUM 502.
was calibrated with a corundum standard and was approximately 58 mm. The ESRF image processing software FIT2D [7] was used for analysis of the two-dimensional diffraction patterns (e.g., averaging, azimuthal integration).
3. Results and discussion As described above, X-ray diffraction data were obtained from single, vertically oriented fibres. The two-dimensional microdiffraction diagrams of the four samples investigated are shown in Fig. 3. The inherent fibre texture, with all cellulose crystals aligned such that the molecules are essentially parallel to the longitudinal fibre axis, leads to a so-called fibre diagram. Orientational properties of the cellulose microfibrils can be seen immediately from the raw data. The azimuthal arcing (broadening) of the Bragg reflections is a direct measure for the internal orientation of the cellulose. Values for the azimuthal width of the cellulose 200 reflection are given in Table 1. Bast textile fibres like flax, hemp, jute or ramie are characterised by a very high orientation of the cellulose microfibrils along the direction of the fibre axis [8]. The two-dimensional microdiffraction diagram of a single fibre of QUM 510 (Fig. 3a) proves these orientational properties. The two-dimensional X-ray diffraction diagram of QUM 525 (Fig. 3b) is characteristic of that of cotton: There are four maxima on the azimuth at the radial position of the 200 reflection. This crossed behaviour indicates a helical fibril structure. For sample QUM 512, the X-ray microdiffraction data (Fig. 3c) displays much less oriented cellulose than e.g.
in QUM 510. The two-dimensional diffraction diagram of the unprocessed plant material QUM 502 is of fibre symmetry with a relatively high degree of orientation, similar to bast fibres. The lateral microfibril size is of great interest as it is very specific for a given plant species [9]. The three strongest cellulose reflections 11¯0, 110 and 200 are found on the equator of the fibre diagram (in Fig. 3a the horizontal symmetry axis). The radial width of these relatively broad reflections contains information about the cross-section dimension of the cellulose microfibrils. To obtain these values, the fibre diagrams were azimuthally averaged in an angular region of about 208 around the equator. The thus obtained one-dimensional diffraction curves contain just the three reflections mentioned above in the range of the wave vector transfer Q=(4p/k) sinQ (scattering angle 2Q) from 8 to 19 nm 1. The peak shape was assumed to be Lorentzian [10], the peak positions were calculated using cellulose lattice parameters [11]. The relevant lattice constants a (given in Table 1), b and g, reflection widths as well as a linear background were free parameters in a least-squares fit to the data. As an example, data and fit for the bast fibre QUM 510 are shown in Fig. 4a (bottom) and are in excellent agreement. The decomposition into the three reflections and the background is given by the dashed lines. The peak widths (given in 2Q) were converted into apparent crystal sizes using the Scherrer equation [12] and listed in Table 1. The most reliable value is obtained from the width of the single 200 reflection, which does not overlap with other peaks. It can be regarded as the diagonal of the cellulose microfibril cross-section.
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Fig. 3. Two-dimensional X-ray microbeam diffraction diagrams of single fibres from (a) QUM 510, (b) QUM 525, (c) QUM 512, (d) QUM 502.
In the case of QUM 510, the crystal size is larger than that expected for flax. On the other hand, there is excellent agreement between the crystallite sizes determined from the least-squares fit for QUM 510 (Fig. 4a, bottom; 5.9 nm) and that of modern ramie (5.7 nm). Furthermore the diffraction diagram for QUM 510 is a perfect match to that of ramie (Fig. 4a, top). Despite this evidence it must be considered that, though unlikely, it is possible that the increase in crystal cross section could be due to ageing effects such as annealing. The azimuthally integrated data for QUM 525 exhibit similar characteristics to that of a modern cotton sample. A plot of the integrated intensity for QUM 525 and for
Table 1 Crystallographic parameters (crystal sizes, calculated from the 200 reflection; lattice constant a; azimuthal HWHM of 200 reflection) of the samples investigated Sample
Crystal size (2)
a (2)
HWHM 200 (8)
Modern flax Modern ramie Modern cotton Primary wall QUM 510 QUM 525 QUM 512 QUM 502
47 57 61 18 59 57 56 30
7.87 7.87 7.88 8.40 7.90 7.86 7.87 8.06
3.5 6.0 No fibre texture Powder texture 6.4 No fibre texture 19.1 7.5
modern cotton clearly illustrates this (Fig. 4b). A leastsquares fit applied to the data yields a cross-section diagonal of about 60 nm for both ancient and modern cotton as given in Table 1. For QUM 512 a crystal size of about 5.6 nm is obtained. This value is quite close to typical microfibril dimensions of bast fibres. There is a high similarity with the diffraction diagram of QUM 510 (Fig. 4c). Despite the high orientation of the cellulose microfibrils in fibre QUM 502, integrated one-dimensional data, however, prove a very low crystallinity. The comparison to a flax diffraction diagram (Fig. 4d) shows up major differences: The 200 peak is found at lower Q, 110 and 11¯0 merge to a single broad peak. Cellulose of this kind is often classified as cellulose IV [13], in contrast to the much more abundant form of native cellulose, I. The larger lattice constants a and b as well as the very broad reflections indicate a poor lateral organisation of the cellulose molecules in the microfibrils of QUM 502. It is still better than that of cellulose IV, which usually occurs in primary plant cell walls [14], not in the dominant secondary walls of fibres relevant for textiles. Cellulose in primary walls, however, is not aligned with the cell axis but rather isotropically oriented. It might thus be that the fibres of QUM 502 are highly degraded. The question remains why all other samples are in an excellent state of conservation. QUM 502 could also be a plant stem not
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Fig. 4. Comparison of azimuthally integrated scattering curves (corresponding to the two-dimensional diffraction diagrams in Fig. 3). (a) Equatorial data of QUM 510 shows the 1–10, 110 and 200 reflection of cellulose. Bottom: fit to the data and deconvolution of the three reflections. Top: comparison to modern flax and ramie. (b) Equatorial curves of QUM 525 compared to modern cotton. (c) Equatorial data of QUM 512 compared to the bast fibre QUM 510. (d) Diffraction curve of QUM 502 compared to primary wall cellulose [14] and the QUM 510 bast fibre.
used for textile making and just by chance found in the same place.
4. Conclusions The non-destructive technique of X-ray microbeam diffraction has been demonstrated to have a number of advantages over microscopic techniques and standard Xray diffraction: (i) only single fibres (a few Am in diameter) of the material are required; (ii) the characteristic orientation distribution of cellulose in different plant fibres can be directly measured; (iii) the high spatial resolution enables one to collect diffraction data that are almost not at all influenced by small adhering soil particles. The crystalline parts (microfibrils) of the cellulose in archaeological plant fibres from the caves of Qumran stayed remarkably intact during their storage period in the caves: The diffraction diagrams from most of the single fibres are as clear as those of the respective modern plant fibres.
Two samples presented in this work prove the particular strength of the X-ray microbeam technique to measure the internal cellulose organisation in plant fibres. QUM 502 is not an intact textile fibre. The low degree of cellulose crystallinity possibly means that the fibres are degraded. The nature of QUM 512 remains unclear: only moderately well oriented, but rather highly crystalline cellulose is not typical for a bast fibre, neither is the unusual triangular cross section of the fibres. QUM 510 certainly is a bast fibre with morphological features very close to flax. There are, however, some differences to modern flax fibres and a great similarity to ramie from a structural point of view. Studies on flax samples from different provenances will be needed for a final identification. The identification of QUM 525 as cotton is unambiguously corroborated by the measured orientation distribution of the cellulose microfibrils. From the archaeological point of view, the presence of cotton is of especial interest since the early history of cotton in Israel is still unclear [15].
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References [1] P.W. Rogers, Fibres in miscellaneous samples from a site in the Dead Sea region, in: J.-B. Humbert, J. Gunneweg (Eds.), Khirbet Qumraˆn et dARn Feshkha, II, Studies of Anthropology, Physics and Chemistry, Academic Press, Fribourg, Vandenhoeck & Ruprecht, Gfttingen, 2003, pp. 287–288. [2] M. Mqller, M.Z. Papiz, D.T. Clarke, M.A. Roberts, B.M. Murphy, M. Burghammer, C. Riekel, E. Pantos, J. Gunneweg, Identification of the textiles using microscopy and synchrotron radiation X-ray fibre diffraction, in: J.-B. Humbert, J. Gunneweg (Eds.), Khirbet Qumraˆn et dARn Feshkha, II, Studies of Anthropology, Physics and Chemistry, Academic Press, Fribourg, Vandenhoeck & Ruprecht, Gfttingen, 2003, pp. 277–286. [3] C. Riekel, New avenues in X-ray microbeam experiments, Rep. Prog. Phys. 63 (2000) 233 – 262. [4] M. Mqller, C. Czihak, G. Vogl, P. Fratzl, H. Schober, C. Riekel, Direct observation of microfibril arrangement in a single native cellulose fiber by microbeam small-angle X-ray scattering, Macromolecules 31 (1998) 3953 – 3957. [5] M. Mqller, C. Czihak, M. Burghammer, C. Riekel, Combined X-ray microbeam small-angle scattering and fibre diffraction experiments on single native cellulose fibres, J. Appl. Crystallogr. 33 (2000) 817 – 819. [6] M. Mqller, R. Hori, T. Itoh, J. Sugiyama, X-ray microbeam and electron diffraction experiments on developing xylem cell walls, Biomacromolecules 3 (2002) 182 – 186.
[7] A.P. Hammersley, S.O. Svensson, A. Thompson, Two-dimensional detector software: from real detector to idealised image or two-theta scan, Nucl. Instrum. Methods A 346 (1994) 312 – 321. [8] A.J. Turner, The structure of textile fibres: VII. The structure of flax J. Text. Inst. 49 (1949) 857 – 868. [9] A.C. O’Sullivan, Cellulose: the structure slowly unravels, Cellulose 4 (1997) 173 – 207. [10] M. Wada, T. Okano, J. Sugiyama, Synchrotron-radiated X-ray and neutron diffraction study of native cellulose, Cellulose 4 (1997) 221 – 232. [11] C. Woodcock, A. Sarko, Packing analysis of carbohydrates and polysaccharides: 11. Molecular and crystal structure of native ramie cellulose, Macromolecules 13 (1980) 1183 – 1187. [12] L. Azaroff, Elements of X-ray crystallography, McGraw-Hill Book. Co, New York, 1968. [13] E.S. Gardiner, A. Sarko, Packing analysis of carbohydrates and polysaccharides: 16. The crystal structures of cellulose IVI and IVII, Can. J. Chem. 63 (1985) 173 – 180. [14] J. LaR Kee Him, H. Chanzy, M. Mqller, J.-L. Putaux, T. Imai, V. Bulone, In vitro versus in vivo cellulose microfibrils from plant primary wall synthases: structural differences, J. Biol. Chem. 277 (2002) 36931 – 36939. [15] A. Sheffer, Notes on cotton textiles found in Israel, Newsl. Archaeol. Text. 9 (1989) 3.
Identification of ancient textile fibres from Khirbet Qumran caves using synchrotron radiation microbeam diffractionB Martin Mqllera,*, Bridget Murphya, Manfred Burghammerb, Christian Riekelb, Mark Robertsc, Miroslav Papizc, David Clarkec, Jan Gunnewegd, Emmanuel Pantosc a
Institut fu¨r Experimentelle und Angewandte Physik der Christian, Albrechts, Universita¨t zu Kiel, Leibnizstr. 19, D-24098 Kiel, Germany b European Synchrotron Radiation Facility, B.P. 220, F-38043 Grenoble Cedex, France c Daresbury Laboratory, Keckwick Lane, Warrington WA4 4AD, UK d Institute of Archaeology, The Hebrew University of Jerusalem, Mount Scopus, Jerusalem, Israel Received 1 November 2003; accepted 26 February 2004 Available online 1 September 2004
Abstract Archaeological textiles fragments from the caves of Qumran in the Dead Sea region were investigated by means of X-ray microbeam diffraction on single fibres. This non-destructive technique made the identification of the used plant textile fibres possible. Apart from bast fibres (mainly flax), cotton was identified which was most unexpected in the archaeological context. D 2004 Elsevier B.V. All rights reserved. Keywords: X-ray diffraction; Synchrotron radiation; Microbeam; Archaeometry
1. Introduction The famous Dead Sea Scrolls were found in the caves of Qumran in 1947. The aim of an extended study on textiles found in Qumran is to find out the type of fibres and relate this information to the archaeological questions surrounding the mysterious Essenes, members of an eclectic religious sect, who are reported to have lived there 2100 years ago. This identification of fibre type is important since some authors suggest that the textile fragments are not from the time before 68 AD when the site of Qumran was destroyed. The information on the textiles will also allow conclusions on the trade of the Essenes in the historical context of the Dead Sea region. B This paper was presented at the International Congress on X-Ray Optics and Microanalysis (ICXOM XVII), held in Chamonix, Mont Blanc, France, 22–26 September 2003, and is published in the special issue of Spectrochimica Acta Part B, dedicated to that conference. * Corresponding author. Tel.: +49 431 880 3860; fax: +49 431 880 1685. E-mail address: [email protected] (M. Mqller).
0584-8547/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2004.07.018
The classical approach to analyse textiles is via optical and electron microscopy. Optical microscopy readily reveals the handedness of spun yarns. The shape of fibres allows for the discrimination between animal and plant fibres. Some characteristics of particular fibre types are also optically visible with the help of polarised light. The next step is a shape investigation in more detail using scanning electron microscopy (SEM) images. The microscopic techniques mentioned above were applied to textile samples from the Qumran sites [1,2], identifying wool and plant fibres like flax and cotton. However, some open questions remained, particularly concerning the plant fibres. The intact textile samples were thus investigated using synchrotron radiation X-ray diffraction with a beam of 0.2 mm in diameter [2]. The non-destructive experiments yielded diffraction diagrams, in which sharp and intense powder diffraction rings were observed. These dominating features stem from the fine mineral particles of the soil adhering to the fibres. The fibre diffraction diagrams of the small cellulose crystallites (typically 4–7 nm in diameter), so-called microfibrils, are
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difficult to resolve because of their diffuse character (small crystallites) and the non-ideal fibre orientation in the spun yarns and woven tissues. Quantitative analysis of the highly complicated resulting diffraction patterns is impossible. The recently established technique of X-ray microbeam diffraction [3] overcomes these difficulties by providing a high spatial resolution of a few Am. A focused synchrotron radiation X-ray beam with a high flux density can be used to collect diffraction diagrams of single fibres of a weakly scattering material like cellulose within a few seconds [4–6]. The aim of this article is to demonstrate the power of the advanced technique of X-ray microbeam fibre diffraction for the precise identification of single archaeological textile plant fibres.
2. Experimental For the present study, four textile fragments made from plant fibres were chosen. The selection was made in order to highlight the strengths of X-ray microbeam diffraction. They were found in different caves of the Qumran site. The numbering corresponds to Refs. [1,2] where the classical analysis (in the sense of the introduction) is reported in detail. Photographs of the samples are shown in Fig. 1. QUM 510 (Fig. 1a) is a heavily soiled fragment of a linen textile, the yarn is spun left-handed; two threads are dyed blue (visible as dark in the black and white
photograph). QUM 525 (Fig. 1b) is very probably cotton, spun right-handed. The fragment QUM 512 (Fig. 1c) is made from left-handed spun plant fibres of unidentified type. QUM 502 (Fig. 1d) represents unprocessed plant material. Fig. 2 shows the corresponding SEM images of the above samples that, together with optical microscopy [1], led to the preliminary fibre identification as stated above. Single fibres of 3–6 mm in length were carefully extracted from the samples. Compared to modern plant fibres, the archaeological fibres were extremely brittle, indicating some degradation of the material. The individual fibres with diameters between 10 and 20 Am were glued to a sample holder (metal frame), which was mounted on a goniometer head and optically aligned with the help of a video microscope. Diffraction patterns were collected at the Microfocus Beamline ID13 at the European Synchrotron Radiation Facility (ESRF, Grenoble, France). Details of the scanning diffraction set-up at ID13 may be found in a recent review [3]. X-rays of 0.096 nm wavelength were used in the experiment. The synchrotron radiation was focused to a spot size of 2 Am using an ellipsoidal mirror and a tapered glass capillary. The sample holder was scanned through the microbeam with an accuracy better than 1 Am. In an automated scan all single fibre samples were subsequently scanned in 20 steps of 3 Am. Acquisition time was 30 s per step. Two-dimensional diffraction patterns were recorded on a MAR CCD detector with 64.4564.45 Am2 pixel size. The sample-detector distance
Fig. 1. Photographs of the four textile fragments from the Qumran site. (a) QUM 510, (b) QUM 525, (c) QUM 512, (d) QUM 502.
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Fig. 2. SEM images of fibres from the textile samples. The scale bar is 100 Am in (a) and (c), 50 Am in (b) and (d). (a) QUM 510, (b) QUM 525, (c) QUM 512, (d) QUM 502.
was calibrated with a corundum standard and was approximately 58 mm. The ESRF image processing software FIT2D [7] was used for analysis of the two-dimensional diffraction patterns (e.g., averaging, azimuthal integration).
3. Results and discussion As described above, X-ray diffraction data were obtained from single, vertically oriented fibres. The two-dimensional microdiffraction diagrams of the four samples investigated are shown in Fig. 3. The inherent fibre texture, with all cellulose crystals aligned such that the molecules are essentially parallel to the longitudinal fibre axis, leads to a so-called fibre diagram. Orientational properties of the cellulose microfibrils can be seen immediately from the raw data. The azimuthal arcing (broadening) of the Bragg reflections is a direct measure for the internal orientation of the cellulose. Values for the azimuthal width of the cellulose 200 reflection are given in Table 1. Bast textile fibres like flax, hemp, jute or ramie are characterised by a very high orientation of the cellulose microfibrils along the direction of the fibre axis [8]. The two-dimensional microdiffraction diagram of a single fibre of QUM 510 (Fig. 3a) proves these orientational properties. The two-dimensional X-ray diffraction diagram of QUM 525 (Fig. 3b) is characteristic of that of cotton: There are four maxima on the azimuth at the radial position of the 200 reflection. This crossed behaviour indicates a helical fibril structure. For sample QUM 512, the X-ray microdiffraction data (Fig. 3c) displays much less oriented cellulose than e.g.
in QUM 510. The two-dimensional diffraction diagram of the unprocessed plant material QUM 502 is of fibre symmetry with a relatively high degree of orientation, similar to bast fibres. The lateral microfibril size is of great interest as it is very specific for a given plant species [9]. The three strongest cellulose reflections 11¯0, 110 and 200 are found on the equator of the fibre diagram (in Fig. 3a the horizontal symmetry axis). The radial width of these relatively broad reflections contains information about the cross-section dimension of the cellulose microfibrils. To obtain these values, the fibre diagrams were azimuthally averaged in an angular region of about 208 around the equator. The thus obtained one-dimensional diffraction curves contain just the three reflections mentioned above in the range of the wave vector transfer Q=(4p/k) sinQ (scattering angle 2Q) from 8 to 19 nm 1. The peak shape was assumed to be Lorentzian [10], the peak positions were calculated using cellulose lattice parameters [11]. The relevant lattice constants a (given in Table 1), b and g, reflection widths as well as a linear background were free parameters in a least-squares fit to the data. As an example, data and fit for the bast fibre QUM 510 are shown in Fig. 4a (bottom) and are in excellent agreement. The decomposition into the three reflections and the background is given by the dashed lines. The peak widths (given in 2Q) were converted into apparent crystal sizes using the Scherrer equation [12] and listed in Table 1. The most reliable value is obtained from the width of the single 200 reflection, which does not overlap with other peaks. It can be regarded as the diagonal of the cellulose microfibril cross-section.
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Fig. 3. Two-dimensional X-ray microbeam diffraction diagrams of single fibres from (a) QUM 510, (b) QUM 525, (c) QUM 512, (d) QUM 502.
In the case of QUM 510, the crystal size is larger than that expected for flax. On the other hand, there is excellent agreement between the crystallite sizes determined from the least-squares fit for QUM 510 (Fig. 4a, bottom; 5.9 nm) and that of modern ramie (5.7 nm). Furthermore the diffraction diagram for QUM 510 is a perfect match to that of ramie (Fig. 4a, top). Despite this evidence it must be considered that, though unlikely, it is possible that the increase in crystal cross section could be due to ageing effects such as annealing. The azimuthally integrated data for QUM 525 exhibit similar characteristics to that of a modern cotton sample. A plot of the integrated intensity for QUM 525 and for
Table 1 Crystallographic parameters (crystal sizes, calculated from the 200 reflection; lattice constant a; azimuthal HWHM of 200 reflection) of the samples investigated Sample
Crystal size (2)
a (2)
HWHM 200 (8)
Modern flax Modern ramie Modern cotton Primary wall QUM 510 QUM 525 QUM 512 QUM 502
47 57 61 18 59 57 56 30
7.87 7.87 7.88 8.40 7.90 7.86 7.87 8.06
3.5 6.0 No fibre texture Powder texture 6.4 No fibre texture 19.1 7.5
modern cotton clearly illustrates this (Fig. 4b). A leastsquares fit applied to the data yields a cross-section diagonal of about 60 nm for both ancient and modern cotton as given in Table 1. For QUM 512 a crystal size of about 5.6 nm is obtained. This value is quite close to typical microfibril dimensions of bast fibres. There is a high similarity with the diffraction diagram of QUM 510 (Fig. 4c). Despite the high orientation of the cellulose microfibrils in fibre QUM 502, integrated one-dimensional data, however, prove a very low crystallinity. The comparison to a flax diffraction diagram (Fig. 4d) shows up major differences: The 200 peak is found at lower Q, 110 and 11¯0 merge to a single broad peak. Cellulose of this kind is often classified as cellulose IV [13], in contrast to the much more abundant form of native cellulose, I. The larger lattice constants a and b as well as the very broad reflections indicate a poor lateral organisation of the cellulose molecules in the microfibrils of QUM 502. It is still better than that of cellulose IV, which usually occurs in primary plant cell walls [14], not in the dominant secondary walls of fibres relevant for textiles. Cellulose in primary walls, however, is not aligned with the cell axis but rather isotropically oriented. It might thus be that the fibres of QUM 502 are highly degraded. The question remains why all other samples are in an excellent state of conservation. QUM 502 could also be a plant stem not
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Fig. 4. Comparison of azimuthally integrated scattering curves (corresponding to the two-dimensional diffraction diagrams in Fig. 3). (a) Equatorial data of QUM 510 shows the 1–10, 110 and 200 reflection of cellulose. Bottom: fit to the data and deconvolution of the three reflections. Top: comparison to modern flax and ramie. (b) Equatorial curves of QUM 525 compared to modern cotton. (c) Equatorial data of QUM 512 compared to the bast fibre QUM 510. (d) Diffraction curve of QUM 502 compared to primary wall cellulose [14] and the QUM 510 bast fibre.
used for textile making and just by chance found in the same place.
4. Conclusions The non-destructive technique of X-ray microbeam diffraction has been demonstrated to have a number of advantages over microscopic techniques and standard Xray diffraction: (i) only single fibres (a few Am in diameter) of the material are required; (ii) the characteristic orientation distribution of cellulose in different plant fibres can be directly measured; (iii) the high spatial resolution enables one to collect diffraction data that are almost not at all influenced by small adhering soil particles. The crystalline parts (microfibrils) of the cellulose in archaeological plant fibres from the caves of Qumran stayed remarkably intact during their storage period in the caves: The diffraction diagrams from most of the single fibres are as clear as those of the respective modern plant fibres.
Two samples presented in this work prove the particular strength of the X-ray microbeam technique to measure the internal cellulose organisation in plant fibres. QUM 502 is not an intact textile fibre. The low degree of cellulose crystallinity possibly means that the fibres are degraded. The nature of QUM 512 remains unclear: only moderately well oriented, but rather highly crystalline cellulose is not typical for a bast fibre, neither is the unusual triangular cross section of the fibres. QUM 510 certainly is a bast fibre with morphological features very close to flax. There are, however, some differences to modern flax fibres and a great similarity to ramie from a structural point of view. Studies on flax samples from different provenances will be needed for a final identification. The identification of QUM 525 as cotton is unambiguously corroborated by the measured orientation distribution of the cellulose microfibrils. From the archaeological point of view, the presence of cotton is of especial interest since the early history of cotton in Israel is still unclear [15].
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