江戸末期に海外より技術移入されたクロムイエロー染色法で染めた絹の微細構造

抄録

  The microstructure of silk fiber dyed by a chrom-yellow dyeing technique imported into Japan in the last Edo period has been investigated. The silk fiber is dyed using lead acetate and potassium chromate solution. The color is measured with a spectrophotometer. The microstructures are observed with a scanning electron microscope and transmission electron microscope. The crystal structure is determined with an X-ray diffractometer. The composition is analyzed using an energy dispersive X-ray spectrometer. A thin film is prepared by the focused ion beam method to observe the nanostructures. The cross section is flattened by ion milling to reduce the damage of the surface. The absorption edge of silk thread dyed is 558 nm (2.2 eV). The edge agrees with that of PbCrO₄. The dyestuff compounds, monoclinic and orthorhombic PbCrO₄, are detected by X-ray diffraction analysis. The PbCrO₄ crystals precipitate on the silk fiber surface; the length and width of the crystals are 0.2~1.2 µm and 0.05~0.4 nm, respectively. Preferential precipitation is observed in the fiber, and most of the precipitates align along a specific direction in the fiber. Fine PbCrO₄ particles with a size of 4~170 nm are also observed in side of the silk fiber. The distribution of precipitates shows that there is a correlation between the precipitation phenomenon and the silk fiber structure. An outline of the microstructures of the silk fiber can be revealed by exploiting the preferential precipitation.