江戸時代後期に輸入された唐桟布(とうざんふ)繊維中の黄色染色剤・PbCrO4 の微細構造

Abstract

The nanostructures of the yellow dyestuff PbCrO4 used for touzan fabric imported in the late Edo period have been investigated. The yellow dyed threads are removed from the fabric and the cross-sectional structures are observed. A thin film is made by the FIB method to observe the nanostructures. The nanostructures are observed by means of transmission electron microscopy. Chromium (Cr) and lead (Pb) are detected by EDX almost constantly from inside the fiber. Fine acicular orthorhombic PbCrO4 crystals are observed in the fiber almost parallel to the fiber direction. The length and width of the crystals are 50~100 nm and 10~20 nm, respectively. Nanometer-sized 3~5 nm rectangular monoclinic PbCrO4 crystals are distributed randomly throughout the fiber. It is thought that the acicular crystals precipitate at defect sites such as the amorphous area of cotton fiber. There is a correlation between the precipitation phenomenon and structural defects of the cotton fiber. On the other hand, referring to a document from the Meiji period, cotton threads available on the market now are actually dyed for various dying times, and the behaviors of Pb and Cr in the fiber are analyzed by EDX in the fiber section. The Cr density in the fiber decreases gradually with distance from the surface. The diffusion length from the surface increases when the processing time becomes long. In the area where Pb coexists with Cr, it is inferred that PbCrO4 is generated. The X-ray diffraction pattern of the dyed threads is confirmed to show the strong peaks of the monoclinic PbCrO4 crystal and the week peaks of the orthorhombic PbCrO4 crystal. Most of the peaks agree with those obtained from touzan cloth.