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At the conservation and restoration facility of the Takamatsuzuka wall paintings, scientific research on coloring materials has been conducted continuously, concurrently with restoration works. The analytical investigation by X-ray fluorescence analysis and visible reflectance spectroscopy has been providing a variety of information about the coloring materials used in the Takamatsuzuka wall paintings. On the other hand, some materials, for example, those used to represent clothes of female figures, are left unidentified yet. In order to analyze those materials using a method independent of X-ray fluorescence analysis and visible reflectance spectroscopy, we have developed a portable X-ray diffraction analyzer by ourselves. After careful safety inspections and the evaluation of the detector, the investigation of the coloring materials used on the paintings referred to as “the Group of Female Figures on the West Wall of Takamatsuzuka Tumulus” was conducted in 2022. As a result, cinnabar, azurite and malachite were directly identified from red, blue and green coloring materials, respectively, for the first time.

Among the twelve zodiac signs in the wall paintings of Kitora Tumulus, the signs of dragon, snake and monkey have not been discovered because they are covered with mud. In order to decide the treatments for restoration, it is important to identify the existence of those signs. Therefore, the authors conducted investigations by X-ray fluorescence analysis. Analyses were conducted on the part of the walls where dragon, snake and monkey were expected to be drawn. The detection of mercury indicated the existence of those paintings beneath the mud.

The present report shows the analytical results of the materials used in Kuno-ji kyo, a national treasure. Kuno-ji kyo is a set of sutras composed of 30 volumes, decorated with gold, silver, and coloring, and produced in the late Heian period (12th century). Volume 5 of Kuno-ji kyo, Yakuso-Yuhon, was recently restored because many of their golden parts had peeled off and the color had changed. Non-destructive investigation using X-ray fluorescence analysis was carried out after the restoration. As a result, both copper and zinc were detected from the boundary lines where the materials had peeled off severely. No gold was detected from the lines. Since the intensity ratio of copper and zinc is almost constant, it can be estimated that the material used for the boundary lines is brass. Brass was used only in the boundary lines and was not found in other colored parts. Careful judgment was needed to determine whether the brass found in the present analysis is original or from subsequent repairs. Up to now, it has been thought that brass began to be used after the early Edo period (16th century). Even if brass was found in a work produced before the Edo period, it was often thought that the work would be an imitation made during and after the Edo period. However, regarding the brass found in the present analysis, it can be judged that the brass is original because there is no data or image to substantiate that brass was used in the past repairs. This analytical result shows that brass was used in the Heian period and in sutras.

The Watanuki-Kannonyama Tomb with a keyhole shape in Takasaki City, Gunma Prefecture, was built at the end of the 6th century. A large number of different kinds of metal objects were excavated from the tomb during 1967-1968. After excavation, conservation treatment was performed and X-ray fluorescence analysis was applied for some objects, but the chemical composition could not be obtained. In 2019, a material analysis using the latest X-ray fluorescence spectrometer was conducted for 44 metal objects, and the chemical composition could be estimated accurately. It has become clear that five types of base materials are used: copper, bronze, iron, silver, and gold. Copper, iron, silver, and gold had a purity of 99% or more. As for bronze and gold, no surface treatment was found. On the other hand, surface treatments have been found on some copper, iron and silver objects. The most common surface treatment for copper objects is amalgam gold gilt. One piece of a copper object with both amalgam gold and silver gilt was found, and is noted as a valuable example. No iron object was found with amalgam gilt. Instead, there are some objects which have a gilt bronze or silver sheet on top of the surface of iron. Some silver products are used without any surface treatment. Amalgam gilt has been found on the surface of silver objects. A thick amalgam gilt over 9 μm was found from a silver object. More than hundreds of metal objects have been excavated from the Watanuki-Kannonyama Tomb. Further material analysis will continue and it is expected that the details of metal composition will become clear.

Among the twelve zodiac signs in the wall paintings of Kitora Tumulus, the signs of dragon, snake and monkey have not been discovered because they are covered with mud. In order to decide the treatments for restoration, it is important to identify the existence of those signs. Therefore, the authors conducted investigation by X-ray radiography. In order to conduct the investigation of the wall paintings safely and efficiently, the conditions for X-ray radiography, for example the tube voltage, were determined in advance by checking the X-ray images of a test piece which reproduces the structure of the wall paintings. As a result of the investigation by X-ray radiography, signs of snake and monkey could not be recognized in X-ray images. On the other hand, an image appeared at the location where the dragon was expected to be drawn. However, the obtained contrast of the X-ray image was opposite to expectation; the transmittance of X-ray around the image looked lower than that on the image. One of the possible reasons is the recrystallization of calcite on the surface of the plaster where no image was drawn.

The Sun and Moon Landscape of Four Seasons collected in Kongoji temple is a pair of six-folding screens that was newly designated as a national treasure in 2018. It is believed to have been produced in the 15-16th centuries. Tokyo National Research Institute for Cultural Properties conducted an analysis of the coloring materials by X-ray fluorescence spectrometry. As a result, unusual use of white pigment was found from other Japanese paintings. It has been found that the white pigment used in Japanese painting changes dramatically from Pb pigment (lead white) to Ca pigment (calcite) in the 15-17th centuries. In paintings drawn at the time of conversion of white pigment, there are worksusing both Pb material and Ca material as white pigment. Pb pigment is generally used to finish a wide area smoothly, and Ca pigment is used to express voluminous sense. However, it was revealed that the opposite use of white pigment was done in the Sun and Moon Landscape of Four Seasons. Ca material was used for the part painted smoothly with white color, and Pb material was used for expression with voluminous sense. Such use of white pigment has never been reported so far and is regarded as a special example.