analysis of pigments used in the scroll paintings of a national

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ANALYSIS OF PIGMENTS USED IN SCROLL PAINTINGS OF
A NATIONAL TREASURE "TALE OF GENJI" USING
A PORTABLE X-RAY FLUORESCENCE SPECTROMETER
Keiichi SUGIHARA1 , Koichi TAMURA1 , Masao SATOH1 ,
Yasuhiro HAYAKAWA2 , Yoshimitsu HIRAO 2 , Sadatoshi MIURA2 ,
Hideki YOTSUTSUJI3 and Yoshitaka TOKUGAWA3
1
2
Seiko Instruments Inc., Chiba, Japan
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 12th 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 19501954. 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 20-30 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 12th century.
In conclusion, this portable XRF analyzer is a powerful tool for non-destructive
investigation of cultural properties.
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4321
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
– www.dxcicdd.com
ICDD Website
- www.icdd.com
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1.
Introduction
X-ray fluorescent spectrometry is widely applied for the qualitative and quantitative
analysis in various fields because of its rapidity and non-destructive ness1),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
recently been developed that can do the elemental analysis at the site4), 5).
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 (9-12th 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 11th 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 objects6). 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.
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2. Experimental
2.1. Equipment
2.1.1. 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
Power Unit
Linearamplifire
Detec
tor
X-ray Tube
D
CC
MCA
High-voltage
Preamplifier
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.
Table 1 The Comparative Table
Size
Weight
Power Supply
X-ray Tube
Detector
X-ray Beam Size
Sample View
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
AC100V/Car Battery
Voltage: 50kV(max)
Current; 1mA(max)
Si-PIN
FWHM: 250eV(@Mn-Kα)
Φ2-10mm
CCD image
Conventional EDXRF
Head(include Power Unit)
1000mm×1000m× 1000mm
Desk-Top PC
>100kg
AC100V
Voltage: 50kV(max)
Current: 1mA(max)
Si(Li)
FWHM: 150eV(@Mn-Kα)
Φ0.1-20mm
CCD image
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2.1.2.
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435
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
Rh-scatter
/
n
+ A
/’
.^K
2
L-
5o.grgkm2
as cus
45.8pgkti
as so
42.lpgkd
Energy(keV)
51.7pgkd
as Al
Fig. 3 Energy dependency
2.1.3. The measurement
as CaF,
-
38.5p g/cd as Ti
L--l
49.5 g/cd as Mn
of sensitivity
setup
The measurement setup is shown in Fig. 4.
4-
Tale of
Genj i
Measurement
Head
- Aluminum
Stand
Wooden
Plate
Fig. 4 The Measurement
Setup
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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.
2.2.
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.
2.3. 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.
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.
Fig. 5 The measured points on part of a scene named “Kashiwagi
Table 2 Typical
Color
I
White
2
3
4
5
Silver
Dark Red
Yellow
Red
Light Red
6
7
8
9
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.
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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 10.
3.2.1. 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
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439
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.
7.0
6.0
5.0
4.0
ocl
3.0
q
2 2.0
G
cl 1.0
2 0.5
.g
* 0.4
e!
.G
2 0.3
a2
2 0.2 nno-
q
A
A
A
0.1
Fig. 7 Intensity
A
Ratio Hg-LP / Pb-LP
3.2.2. Ca (calcium) as a major component in white pigment (Figure 8)
There are only a few measurement points on the
17.72 cps
A I
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.
3.2.3. 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
ws.%o7.spc
14.47 kaV
Fig. 8 Spectrum of the scene
“Sawarabi”
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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.
3.2.4. 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.
i
Fig.10 Spectrum of the scene
Conclusions
“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
Detection characteristics of the portable X-ray fluorescent spectrometer were
extensively examined and its ability to measure cultural artifacts confirmed.
iii
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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