ANALYSIS OF PIGMENTS USED IN SCROLL PAINTINGS OF A NATIONAL TREASURE "TALE OF GENJI" USING A PORTABLE X-RAY FLUORESCENCE SPECTROMETER

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1 Copyright(c)JCPDS-International Copyright(c)JCPDS-International Centre Centre for for Diffraction Diffraction Data Data 2001,Advances 2001,Advances in in X-ray X-ray Analysis,Vol.44 Analysis,Vol ANALYSIS OF PIGMENTS USED IN SCROLL PAINTINGS OF A NATIONAL TREASURE "TALE OF GENJI" USING A PORTABLE X-RAY FLUORESCENCE SPECTROMETER Keiichi SUGIHARA 1, Koichi TAMURA 1, Masao SATOH 1, Yasuhiro HAYAKAWA 2, Yoshimitsu HIRAO 2, Sadatoshi MIURA 2, Hideki YOTSUTSUJI 3 and Yoshitaka TOKUGAWA 3 1 Seiko Instruments Inc., Chiba, Japan 2 Tokyo National Research Institute of Cultural Properties, Tokyo, Japan 3 Tokugawa Art Museum, Aichi, Japan Abstract X-ray fluorescence spectrometry (XRF) is frequency applied for the measurement of the chemical composition of cultural properties because of its rapidity and non-destructiveness. However, it is hard to analyze a sample at the site by conventional XRF. In order to solve this problem, a portable XRF has been developed. The pigments used in the Scroll Paintings of the Tale of Genji in the possession of the Tokugawa Art Museum have been analyzed by portable XRF. This instrument was brought into the museum to avoid various risks that may be caused by moving the paintings. The Scroll Paintings of the Tale of Genji are considered as most important in understanding the materials and techniques of painting in the 12 th century. The pigments used in the fifteen illustrated sheets in the museum were once estimated by an examination using X-ray radiography and ultra-violet fluorescence spectroscopy in However, the elements and the compounds of the pigments have not been identified yet. In this study, the elements of the pigments were measured by using an X-ray beam with Φ2mm diameter. As a results of measurement of about points per each illustrated sheet, composition of pigments corresponding to different colors were identified. For example, 4 kinds of white pigment were detected; major component are (1) Pb (2) Ca (3)Hg (4) not detectable. It was also made clear that the white pigments consisting mainly of Pb used for drawing a human face contains a trace of Hg. Furthermore, the color used for drawing the human face was slightly different between illustrated sheets. This study might give some understanding the material and techniques of painting in the 12 th century. In conclusion, this portable XRF analyzer is a powerful tool for non-destructive investigation of cultural properties.

2 This document was presented at the Denver X-ray Conference (DXC) on Applications of X-ray Analysis. Sponsored by the International Centre for Diffraction Data (ICDD). This document is provided by ICDD in cooperation with the authors and presenters of the DXC for the express purpose of educating the scientific community. All copyrights for the document are retained by ICDD. Usage is restricted for the purposes of education and scientific research. DXC Website ICDD Website -

3 Copyright(c)JCPDS-International Copyright(c)JCPDS-International Centre Centre for for Diffraction Diffraction Data Data 2001,Advances 2001,Advances in in X-ray X-ray Analysis,Vol.44 Analysis,Vol Introduction X-ray fluorescent spectrometry is widely applied for the qualitative and quantitative analysis in various fields because of its rapidity and non-destructiveness 1),2). This method has been used in the field of cultural artifacts for a long time and still today is the one analysis method used most frequently in performing composition analysis of material. In recent years, many new functions, including X-ray incidence capability at an order of µm, elements distribution mapping function, and the ability to measure samples that exceed 1 meter in size, have developed in the field of fluorescent X-ray spectroscopy 3). However analytical samples had to be brought to and placed in a sample chamber because the conventional instruments are large and immovable. In the field of cultural artifacts there are many instances in which the sample cannot be transported, and even if the sample can be transported, it can be damaged during transporting or by changes in temperature and humidity. Besides, there have been vigorous requests for a tool that can immediately analyze unearthed artifacts at the excavation site. In order to accomplish these demands, a portable fluorescent X-ray analyzer has 4), 5). recently been developed that can do the elemental analysis at the site A newly developed portable fluorescent X-ray analyzer was applied for the identification of pigments used in a Japanese national treasure scroll paintings "Tale of Genji". The paintings occupy an important position in art history as representations of Heian Period (9-12 th century) art. The paintings were illustrated on papers about the typical scenes of the romantic novel of "Tale of Genji", which written toward the beginning of the 11 th century by a court-lady known as Murasaki-shikibu. Up until recently, there has been much discussion in terms of art history, but only one examination of scroll paintings using the scientific method. From 1949 to 1953, the predecessor of Tokyo National Research Institute of Cultural Properties performed a systematic examination using optical methods to appraise old art objects 6). Detection of glue, paint-over, and peeling-off of paint was performed by observing enlarged photographs and photographing with infrared/ultraviolet lighting. X-ray radio graphy was also applied for the estimation of material and thickness of the pigments. This examination used the leading edge inspection and analysis technology available at that time. However, adequate conclusions could not be made for the pigments used, or the reason of color change or slightly different tints. Our analysis was able to directly detect elements composition within the pigment. "Tale of Genji" scroll paintings is now separated and mounted on a folding mat with the size of 60cm x 35cm maximum respectively for conservating. Although conventional tools can analyze the painting, a portable X-ray fluorescent spectrometer was taken to the Art Museum to avoid any risk by transporting the paintings outside the museum.

4 Copyright(c)JCPDS-International Copyright(c)JCPDS-International Centre Centre for for Diffraction Diffraction Data Data 2001,Advances 2001,Advances in in X-ray X-ray Analysis,Vol.44 Analysis,Vol Experimental 2.1. Equipment Analyzer Seiko Instruments Inc, SEA200 energy dispersive X-ray spectrometer, the Portable XRF Element Monitor was used. A rhodium X-ray tube (5kv,15kV or 50kV 3-step switching) and maximum current of 1000 µa was equipped. A schematic diagram is given in Fig.1. and the scene where this instrument s is used is given in Fig.2. Sample Linearamplifire Power Unit CCD X-ray Tube Detector Preamplifier High-voltage MCA Measurement Head Lap-top PC Fig. 1 Schematic diagram Fig. 2 Measurement Head The X-rays irradiated from the top. The size of the X-ray beam was adjusted in the range of Φ2-10mm by a collimator. The analysis spot can be observed by the CCD image, resulting that the primary X-rays precisely irradiated the analysis spot. The comparative table is given in Table 1 between the portable EDXRF and the conventional EDXRF. Size Weight Table 1 The Comparative Table Portable EDXRF Head: 185(W) 210(H) 320(D)mm Power Unit : 400(W) 200(H) 300(D)mm Lap-Top PC Head: 5kg Power Unit : 15kg Conventional EDXRF Head(include Power Unit) 1000mm 1000m 1000mm Desk-Top PC >100kg Power Supply AC100V/Car Battery AC100V X-ray Tube Voltage: 50kV(max) Voltage: 50kV(max) Current; 1mA(max) Current: 1mA(max) Detector Si-PIN Si(Li) FWHM: 250eV(@Mn-Kα) FWHM: 150eV(@Mn-Kα) X-ray Beam Size Φ2-10mm Φ0.1-20mm Sample View CCD image CCD image

5 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol Sensitivity Energy dependency of sensitivity was investigated previous to the analysis of the scroll paintings of Tale of Genji. 6 kinds of reference materials, which were deposited thin film on Mylar, were measured. The spectrum for each reference material is given in Fig.2. Al, SiO and CuS were analyzed under He gas purge condition. Each peak of Al, Si and S is clearly observed. S Ti n Rh-scatter + A / /.^K 2 Energy(keV) 5o.grgkm2 as cus 45.8pgkti as so 51.7pgkd as CaF, - L- 42.lpgkd as Al 38.5p g/cd as Ti L--l 49.5 g/cd as Mn Fig. 3 Energy dependency of sensitivity The measurement setup The measurement setup is shown in Fig. 4. Tale of Genj i Wooden Plate 4- Measurement Head - Aluminum Stand Fig. 4 The Measurement Setup

6 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol The scroll paintings were placed on a wooden board and the wooden board was then placed below a 10 mm aluminum stand combined with the analyzer stand. The portable fluorescent X-ray analyzer was set at the center on top of the stand with the X-ray beam direction facing down. The scroll painting was arranged 10 mm from the X-ray unit. The X-ray beam was 2 mm in diameter. With the main part of the instrument secure on top of the stand, the analysis position can be monitored by the CCD camera image displayed on the monitor. The analysis position was then set by manually moving the wooden board on which the scroll paintings are placed Measurement conditions When measuring light elements it is best to measure at a high sensitivity while purging He gas. In this case we measured in air without a He gas purge to avoid He gas blowing on the samples during the measurement. These results performed on many pigment sample fragments using a 2 mm X-ray beam, tube voltage at 50 kv, tube current at 50 ua, and a measurement time of 100 seconds, verified that measurements can be performed on many elements at a statistical deviation of 3% to 5%. The deciding factor to analyze the scroll paintings at these measurement conditions was based on these results Sections Measured The measurement conditions listed above were used to analyze the pigment on all 15 scroll paintings and two text scrolls of the "Tale of Genji." There are considerable color differences from area to area, and the number of measurement points differ depending on the scene. However, we tried to be comprehensive in measuring areas that show characteristic colors in all scenes. We measured many points in areas of severe discoloration or where evaluating original color is difficult. Each scene has roughly 20 to 30 measured points; however, scenes that had many tints had as many as 80 measured points. Figure 5 shows the measured points on part of a scene named "Kashiwagi (Oak Tree)- 3 ". Our measurements gave emphasis to the human face. In this example we measured three points on the face of the man (nose, cheek and lips), and three points on the face of the child (forehead, cheek and lips). We also measured the parts of characteristic colors, for example a faded part and silver design of the man's kimono and areas showing like the green of the tatami mat. 3. Results and Discussion 3.1. Measurement Results Figure 6 shows an example of information displayed on the monitor during the measurement. Figure 6 was obtained by measuring part of the nose of the man in figure 4. The fluorescent X-ray spectrum is displayed in real time and elements contained can be directly identified along with being able to verify measurement points by CCD camera image. Measurement conditions are displayed on the screen at the same time and immediately after the measurement results can be analyzed quantitatively. In this investigation we measured over 500 points in all paintings and texts. The typical colors and detection elements in this investigation along with the pigments listed in Table 2.

7 Copyright(c)JCPDS-International Copyright(c)JCPDS-InternationalCentre Centrefor fordiffraction DiffractionData Data2001,Advances 2001,AdvancesininX-ray X-rayAnalysis,Vol.44 Analysis,Vol.44. Fig. 5 The measured points on part of a scene named Kashiwagi Table 2 Typical Color I White Silver Dark Red Yellow Red Light Red IO I1 Brown Yellow Green Blue Purple Black (Oak Tree)- 3 pigments detected in Tale of Genji Main Sub Pb Ca Pb,Ag Hg,Pb Pb Hg %Hg Pb Pb cu cu Pb Cu,Fe (C&Fe) (Cu) Fe,Pb Fe,Pb (Cu> Estimated Pigments White Lead (+Cinnabar) Shell White Silver Cinnabar Red Lead White Lead + Cinnabar White Lead + dyes White Lead+dyes Malachite Azurite White Lead The main component in white pigment is thought to be white lead (Pb). Our measurements support this position, that is, that Pb is usually the main component. However, trace amounts of Hg were detected in white color of human faces. It is conceivable that trace amounts of cinnabar(hgs) was mixed in the white lead and its color showed white included a tinge of red. We could also observe that the white color included large amounts of Ca but without Pb. Other elements different than these were also detected in the white part, and will be described in the next section

8 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol The large peaks detected at various measured points with various color were Pb. This is probably due to the white lead applied to the base on a paper. In other case, at measured points of yellow areas the only element detected was lead. This seems to support the idea that "Fuji yellow (Gamboge, organic) " was used as the color for yellow. That only white lead is detected in the bottom layer may be due to the fact that most organic material could not be detected in this analysis. Refer to Table 2 concerning other colors and elements detected herein. Fig. 6 Information displayed on the monitor 3.2. Results of measuring white pigments The results of measuring 15 paintings from "Tale of Genji" scroll paintings show that at least four types of materials were used to represent the color white. The typical fluorescent X-ray spectrum of each material is shown in Figures 8 to Pb (lead) as a major component in white pigment (Figure 6) We thought that white lead would be the basic white pigment. Spectrum nearly the same as the one in Figure 4 was obtained by measuring many points on white areas. In many cases, trace amounts of mercury were detected in the facial area, which color is thought to contain a small amount of cinnabar. Figure 7 shows comparative results about the amount of mercury used for drawing human faces or skins. Three representative scenes, which are Kashiwagi (Oak Tree)- 3 as scene A, Takekawa (Bomboo River)-2 as scene B and Hashihime (Bridge Princess) as scene C, with a lot of coloration were selected. The vertical axis in the

9 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol figure is the intensity ratio (Hg Lp / Pb Lp).. The ratio of Hg-LP/Pb-LP in scene A and B, which have some deviation, show nearly the same values. It is clear that scene C has a much larger value than the values of the Hg-LP/Pb-LP ratios obtained from scene A and B. If mercury (Hg) is a reflection of the red of cinnabar, then we can conclude that the red in the skin of the empress in scene C is much stronger than for humans drawn in scene A and B ocl 3.0 q G 1.0 cl g * 0.4 e!.g a nno- A A A A q Fig. 7 Intensity Ratio Hg-LP / Pb-LP Ca (calcium) as a major component in white pigment (Figure 8) There are only a few measurement points on the face of the court lady in figure 8. Ca is the main component without Pb. Ca as the main component suggests that the white color is from shell white (created by grinding shells). We were unable to determine if this pigment was used as drawing at original or was an added later restoration cps A I ws.%o7.spc Hg (mercury) detected in large amounts in white pigment (Figure 9) There are several measurement points on the face of the court lady and young nobleman. In the example shown in Figure 9, the amount of Hg is greater than the pl-----~~ 3.12 kev kav Fig. 8 Spectrum of the scene Sawarabi

10 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol amount of Pb. There are several possible reasons for this including whether Hg existed in white pigment as a major ingredient, or a complex paint-over was done No main component element detected in the white pigment (Figure 10) Other areas were discovered in which no major element was detected in the white. As is clear from figure 10, the spectrum is almost at background level and fluorescent X-ray peaks for the most part cannot be detected. An earlier researcher concluded that this was part of white ground paper where paint had not been applied. However, our measurements made clear that something had been applied on a paper and was not just ground paper. Detecting light elements cannot be done under these measurement conditions. If, for example, pure white clay containing as main components Al and Si were used, measurement results like those in figure 10 would be obtained. It might be expected that the organic dye with white color, which cannot be detected by X-ray fluorescent spectrometry, was used. Fig. 9 Spectrum of the scene Hashihime 4. Conclusions i Fig.10 Spectrum of the scene Yomogiu A portable X-ray fluorescent spectrometer that can be carried almost anywhere was recently developed. This instrument can be taken to the sample location and used to perform rapid elemental analysis. ii iii Detection characteristics of the portable X-ray fluorescent spectrometer were extensively examined and its ability to measure cultural artifacts confirmed. Paints used in scroll paintings of Japanese national treasure the Tale of Genji at the Tokugawa Art Museum were analyzed using the portable X-ray fluorescent spectrometer. The Tokugawa Art Museum has in its possession 15 scroll paintings. On the average, 20 to 30 measurements (maximum of 80) were taken at different points on each scene resulting in our acquiring a large amount of new information, such as the existence of four kinds of white pigment, and color differences attributed to scenes. The authors wish to thank Ms. Miho Yoshikawa of Tokugawa Art Museum, Mr. Yonekura, Mr. Shimao and Mr. Tsuda of Tokyo National Research Institute of Cultural Properties for their cooperation on this work.

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