A Bitter Truth

The elimination of pentachlorophenol in the 1980s, and the ban on chromated copper arsenate (CCA) as the preeminent wood preservative in 2004, brought a great deal of attention to wood preservatives and their impact on health and environmental safety. Currently, most wood preservatives are considered restricted pesticides, and their regulation makes very few products available for safe application on in-service materials. This also calls into question the ethics of using toxic and permanent preservatives on curated items such as historic building fabric. This thesis discusses the potential for a sustainable bio-alternative wood preservative, derived from the astringent persimmon fruit of Diospyros kaki. Past research has identified and studied dozens of individual compounds in the genus Diospyros; many of these extractives are now known to be bioactive as fungicides, termiticides, antiseptics, and free-radical reducing compounds. The genus Diospyros (syn. Persimmon, ebony) is widely distributed in most tropical and subtropical areas of both hemispheres with over 350 species, and a long cultural and agricultural history on several continents. A review of current literature shows a connection between the known traditional use of persimmon-derived coatings and the experimental use of persimmon tannin. The research presented in this thesis provides a preliminary review of two products as tested for both qualitative and quantitative properties. The tests sought to ascertain the character of the water resistant coating, the retention of the treatment, and their efficacy as a protectant against fungal sources. Visual studies on the color palette (and color variability with exposure to weathering) are also presented, along with observations on the interaction of these persimmon-derived products with iron oxide. Droplet testing showed significant water resistance from the kakishibu as long as the coating is maintained; leaching tests indicated that kakishibu has comparable preservative permanence to the tested control, copper naphthenate. Soil-block culture analysis, despite the inconclusive mass loss data, provided valuable qualitative data on surface mold growth deterrence. The color variation tests showed a surprising result of darkening over time for the treatments, a feature that has been confirmed by textile artists working with kakishibu as a dye. The exploration of persimmon's reaction with iron oxide, common on iron fasteners in historic buildings, showed rapid visible change and a glossy well-adhered film with the raw juice, versus a less stable film with kakishibu. In summary, the forms of persimmon fruit studied in this research showed significant promise as bio-alternative wood preservative.