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