江戸時代後期の国産唐桟布(とうざんふ)に用いられた橙色染色剤・Pb₂CrO₅ の繊維内分布と微細構造

抄録

  The distribution and nanostructure of the orange dyestuff compound, Pb₂CrO₅, in cotton fiber used for touzan fabric made in the late Edo period have been investigated. Dyed fiber specimens are taken from old touzan fabric. To observe the distribution of nanometer-sized compound grains in the fiber, the cross section of the fiber is flattened by ion milling after mechanical polishing. The macrostructure is observed by X-ray CT. The nanostructure is observed by SEM and TEM. The composition and crystal structure are analyzed by EDS, XRD and ED. The dye compound, Pb₂CrO₅, is mainly detected by EDS and XRD. Fine acicular precipitates of Pb₂CrO₅ are aligned along the fiber, forming concentric circles. The Pb₂CrO₅ needlelike crystals have lengths and widths of 100~300 nm and 20~50 nm, respectively. However, the needlelike precipitate consists of an aggregation of many nanometer-size Pb₂CrO₅ crystals. Preferential precipitation is observed at cracks in the fiber, and precipitation-free zones near the fiber surface, in the area of the fiber lumen and in the area near the crack are also observed. It is thought that the Pb₂CrO₅ nano-crystals nucleate and grow in the amorphous area in the fiber. A possible nucleation and growth model of the Pb₂CrO₅ crystal is proposed.