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.