A field survey of kozo (paper mulberry) cultivation and the application of wood ash in washi paper-making

Applying agricultural sheets to prevent weed growth as part of cultivating kōzo.

Mr. Fukunishi explaining about kōzo raw material.

　Although a wide range of tools and raw materials are used in the preservation and restoration of cultural property, fine arts, and crafts, many are at risk of being discontinued in the future due to a lack of skilled successors and increasing difficulty in securing the necessary materials. In response to this situation, the Center for Conservation Science, Department of Intangible Cultural Heritage, and the Department of Art Research, Archives and Information Systems at the Tokyo National Research Institute for Cultural Properties (TOBUNKEN) has been involved in the commissioned research of “Investigation of Tools and Materials Used for the Preservation and Restoration of Fine Arts and Crafts” as part of the project of the Agency for Cultural Affairs, “Support for the Management of Tools and Materials Used for the Preservation and Restoration of Fine Arts and Crafts.” This report introduces a field survey of the cultivation of kozo (paper mulberry), the raw material for washi (Japanese paper), which is essential for the restoration of cultural property. It also presents the current use of wood ash in the cooking process used to obtain kozo fibers.

　We visited four kozo fields in Yoshino Town and Gojo City, Nara Prefecture, on June 9-10, 2025, and learned about the meticulous work involved in tasks called mekaki (the removal of unnecessary new shoots and buds to concentrate nutrients on the remaining ones) and weed control, as well as the various innovations and challenges involved in the cultivation process. There is no end to the challenges, such as determining the cause of “red streaks” that appear on the inner bark, which reduce the usable amount of raw material because they discolor the fibers, and dealing with insects that were not seen in the past. The number of people responsible for this type of cultivation management is decreasing year by year, which poses a significant challenge in terms of ensuring a stable supply of this raw material.

　We also visited the paper-making factories of Mr. FUKUNISHI Masayuki and Mr. UEKUBO Ryoji. The raw materials and wood ash are carefully selected and the delicate process of removing inclusions one-by-one by hand is repeated, because such inclusions make the material unsuitable for the restoration of cultural property. The issue of ensuring a stable supply of wood ash in the future was also discussed. An alkaline solution obtained from wood ash is essential for extracting kozo fibers, but it is also becoming increasingly difficult to procure the ash to obtain good quality fiber.

　Going forward, we will conduct scientific research into the interactions between ash derived from various plant species and various raw materials and woods, with the aim of addressing specific challenges. In parallel, we will focus on strengthening our role as a network hub, connecting experts and knowledge across related fields, while continuing our ongoing efforts to document production techniques and processes.

Video Recording of Noriutsugi Harvesting and Inspecting the Dissemination Activities in Shibetsu Town

Peeling bark from a tree using a customized spoon

Peeling off the outer parts and extracting the inner parts

Children focusing on washi-making with Mr. Fukunishi

People engaged in noriutsugi supplies intently listened to the explanation by Mr. Fukunishi

　“Neri,” a substance extracted from noriutsugi trees, is essential for making Uda washi (Japanese traditional paper) that is used for cultural property restoration. Under the strong sunshine in early summer, people in Shibetsu Town, Hokkaido, carefully remove bark from noriutsugi and peel off its outer parts by hand to extract the inner parts. Furthermore, to reduce reliance on the wild species, they have begun to grow noriutsugi trees in nurseries.

　Four members of the Tokyo National Research Institute for Cultural Properties (TOBUNKEN), Mr. NISHIDA Noriyoshi, Head of Analytical Science Section, Center for Conservation Science, Ms. ICHIMIYA Yae, Associate Fellow of the same Center, Ms. MAEHARA Megumi, Head of Intangible Cultural Properties Section, the Department of Intangible Cultural Heritage, and Mr. ODAWARA Naoya, Associate Fellow of the same Department, visited Shibetsu Town from June 24 to 27, 2025. They inspected the process of barking noriutsugi and peeling off its outer parts, and video-recorded the way to grow nursery trees with talks provided by the related parties. They also participated in and video recorded dissemination activities, including a workshop by Mr. FUKUNISHI Masayuki, a holder of selected conservation techniques for handmade washi essential for mounting (Uda washi paper) held at the Shibetsu Town Culture Hall, targeting elementary school students and the wider public. These videos are planned for use in research, education, and dissemination related to the succession of cultural properties after editing.

　TOBUNKEN concluded an agreement on collaboration and cooperation on materials for cultural property restoration with Shibetsu Town on November 2, 2023. Recording and disseminating the activities to ensure sustainable supplies of noriutsugi and dissemination activities are expected to benefit this collaboration and cooperation.

Newly Introduced/Updated Instruments at the Center for Conservation Science in FY2024

　In FY2024, the Conservation Science Center newly installed a Raman spectrometer, a 3D fluorescence spectrophotometer, and a high-performance liquid chromatography system, and updated the existing pyrolysis GC/MS and ion chromatograph. These instruments are introduced below. (Figure 1)

Raman spectrometer
　When a material is irradiated with laser light, the wavelength of Raman scattered light changes depending on the molecular structure of the material at the point of irradiation. Using this principle, it is possible to analyze the structure of a sample in a non-contact and non-destructive manner. For this purpose, we have introduced three types of instruments: a stationary Raman microspectroscope that can also be used for mapping, a portable Raman microspectroscope that can be carried around, and a hand-held Raman spectroscope that is compact and easy to carry around. Raman spectroscopy can be used to analyze any sample other than pure metals, whether inorganic or organic. It can be used for various applications such as identification of dyes and pigments, elucidation of the causes of corrosion, and analysis of adhering materials on cultural properties. (Figure 2)

Three-dimensional spectrofluorometer
　Since the wavelength and intensity of fluorescence emitted from a sample varies depending on its structure, fluorescence analysis can be used to estimate the structure of materials constituting cultural properties. It is a non-contact, non-destructive measurement method and can be used to analyze any sample that emits fluorescence. There are a surprisingly large number of samples that emit fluorescence (for example, fluorescence can be detected in cloth, paper, and wood in many cases), and many cultural properties can be analyzed using this method, but it is a particularly powerful analysis tool for dyes. (Figure 3)

High-performance liquid chromatography system
　Used for the determination of aldehydes in the air and dyes in textiles, this system is equipped with a PDA detector, which is more powerful than a typical UV detector for identifying unknown substances. Since extraction is required, this is basically a destructive analysis method.

Pyrolysis GC/MS (updated)
　This instrument is capable of analyzing in detail the structure of samples consisting of polymers, such as paper, fabric, lacquer, and wood. Although it is a destructive method, it is possible to analyze even a very small amount of sample (1 mg). Qualitative quantification of atmospheric odors and residual solvents is also possible.

Ion chromatograph (updated)
　This is used for the quantitative determination of ammonia and organic acids in the air, and chloride and nitrate ions in water. It employs a suppressor method and is extremely sensitive.

　We will continue to analyze cultural properties using these instruments.

It can be seen that the spectra obtained are different depending on the material colorant. A resolution of 1 µm enables identification of the colorant material. In particular, the ability to analyze inksticks nondestructively is a major feature. In addition to pigments, a wide variety of samples can be analyzed, including dyes, minerals, metal corrosion, and fibers.

Accelerated aging test causes an overall decrease in fluorescence intensity. In particular, there are marked decreases in fluorescence intensity around the excitation wavelength of 280 nm and fluorescence wavelength of 420 nm. Since the fluorescence pattern changes depending on the degree of deterioration and the material itself, it is useful for evaluating the degree of deterioration and for analyzing the differences between different materials.

Newly introduced instruments at the Center for Conservation Science in FY2023

　In FY2023, the Center for Conservation Science introduced a microtome, a biological microscope (with polarized light, phase contrast, and differential interference observation functionality), and an infrared microscope (Fig. 1). The following is an introduction of these newly introduced instruments.

Microtome
　The microtome is a device used to precisely cut samples to facilitate observation. For example, when analyzing what kind of material a piece of paper or cloth is made of, a sample is sometimes cut and its cross section is observed under a microscope. Conventionally, samples are cut with razor-sharp blades or embedded in resin and polished. However, these methods can present problems such as deformation of the specimen and difficulty in observing the specimen because it is embedded in resin, and they require skillful manipulation. The microtome solves these problems and makes it easier to identify paper and cloth materials. Figure 2 shows an example of actual cross-sectional observation results. The microtome can be applied to all cultural assets made of organic materials such as wood and lacquerware.

Biological Microscope
　Polarized light observation, phase-contrast microscopy, and differential interference microscopy are effective for observing crystal structures, microstructures, and cells and biological tissues, respectively. For example, they are effective for observing mold and bacteria on cultural properties, fibers of paper and textiles, and starch glue and other glues used for cultural properties.

Infrared microscope
　Infrared cameras are often used to observe cultural properties. This type of microscope can be used to clearly see ink lines and certain types of dyes used in calligraphy and paintings, and to identify materials and observe the underlying surface of paintings.

　We will continue to analyze cultural properties using these devices.

Figure 1. Photographs of newly introduced instruments

Microtome

Biological microscope

Infrared microscope

Figure 2. Cross section of Najio Gampi paper

Cross-section produced using a scalpel

Cross-section produced using a microtome

　When a scalpel is used to produce a cross section, a large amount of clay minerals are pressed down by the blade, covering the gampi fibers and causing them to lose their original shape. When the cross section is produced with a microtome, the gaps between fibers can be confirmed, and the hollow structure of the fibers remains intact.

Study for a Stable Supply of Noriutsugi (2)

　In our December 2022 Monthly Report, we reported on the “neri,” a sort of “dispersant” used in papermaking, extracted from noriutsugi (Hydrangea paniculate). This report is a continuation of that previous report.
　Since last year, noriutsugi collected in Shibetsu-cho, Hokkaido Prefecture has been shipped to various papermaking areas and used as neri for papermaking, but problems such as blackening of the neri have been observed in some areas. Analysis of the causes of the blackening confirmed that it is caused by a combination of three conditions: heating during neri extraction, contamination of tannins in the outer bark, and the absence of preservatives. Therefore, the blackening can be eliminated by carefully removing the outer bark or by adding a small amount of preservative. This result was reported at the 45th annual meeting of The Japan Society for the Conservation of Cultural Property (National Museum of Ethnology, June 24-25), and the presentation was very fruitful, receiving many questions.
　In addition, we visited the production sites of Uda paper (Yoshin-cho, Yoshino-gun, Nara Prefecture) and Echizen washi (Echizen-shi, Fukui Prefecture), which are made using noriutsugi, in succession (March 6 for Uda and July 19 for Echizen) and conducted a survey of the paper-making process. In both of these production areas, the shortage of noriutsugi is a major problem, and the supply from Shibetsu-cho is expected to be of great help. It was also confirmed once again that there are different ways to use noriutsugi neri depending on the production area and the craftsman, and it is necessary to consider supply methods that meet the needs.　In addition, on July 27, we visited Shibetsu-cho to observe the collection of noriutsugi bark, to study the collection method and to record and photograph the process. This year, about 200 kg of noriutsugi bark has already been collected and shipped to various papermaking regions.
　We will continue our activities to ensure a stable supply of noriutsugi.

Uda-gami papermaking, using noritsugi from Shibetsu-cho

Noritsugi used for Echizen washi

Noriutsugi, which grows wild in large quantities in Shibetsu-cho

Collecting bark

Investigation for Sustainable and Stable Supply of Noriutsugi

Noriutsugi
Neri is extracted from noriutsugi bark. The yellow part of the tree is where bark has been removed.

Discussion meeting in TOBUNKEN

　Washi (Japanese traditional paper) is used for the restoration of cultural properties and for traditional crafts. It is well known that washi is made of fibers extracted from plants such as kōzo (Broussonetia kazinoki x B. papyrifera) and ganpi (Diplomorpha sikokiana). However, it is not widely known that neri, a dispersant, is also essential for washi making. Adding neri disperses the fibers evenly in water, producing smooth and beautiful washi. Without the addition of neri, the fibers are not evenly dispersed, and washi made without neri has poor formation.

　Including washi most cases of industrial mass paper manufacturing use synthetic compounds such as polyethylene oxide as neri. Traditionally, neri is made from mucilage extracted from plants such as tororoaoi (Abelmoschus Manihot) and noriutsugi (Hydrangea paniculate). At present, neri extracted from tororoaoi or noriutsugi is still most suitable for thin washi making. It is also widely used for washi-making for cultural property restoration. However, the sustainable and stable supply of these raw materials, especially noriutsugi, becomes increasingly difficult. This is because noriutsugi for neri is a wild species and there are not enough successors to the experts with knowledge on locating noriutsugi and removing its bark. If the low amounts of noriutsugi available does not change, this will permanently impair washi-making for the restoration of cultural property. For example, uda washi paper used for soura-kami (the final lining paper) of hanging scrolls is made using neri extracted from noriutsugi. Therefore, we are concerned that restoring hanging scrolls will become difficult in the near future.

　Commissioned by the Agency for Cultural Affairs, the Center for Conservation Science has been conducting a research project: “Investigation of Tools and Materials Used for the Preservation and Restoration of Fine Arts and Crafts” with the Department of Art Research, Archives and Information Systems and the Department of Intangible Cultural Heritage. As an important investigation of this project, we are working for sustainable and stable supply of noriutsugi. This investigation is conducted in cooperation with Hokkaido Prefecture, Shibetsu Town and others. We visit the noriutsugi growing area in Shibetsu Town and hold regular discussion meetings. We will provide supports for sustainable and stable supply of noriutsugi and conduct scientific studies on why neri extracted from noriutsugi shows such excellent characteristics.