江戸時代の浮世絵版画に用いられたフェロシアン化鉄顔料の劣化

抄録

  The deterioration mechanism of ferric ferrocyanide (Fe₄[Fe(CN)₆]₃·xH₂O) which is called Prussian blue, used as a blue pigment in Ukiyo-e printed in late Edo period, has been investigated. The two Ukiyo-e of the same design differ in their degree of deterioration; one print has good color, but the other is seriously discolored. The conditions of their blue areas are compared. The composition of the Ukiyo-e color pigments are analyzed by EDS (Energy Dispersive X-ray Spectroscopy). FT-IR (Fourier Transform infrared Spectrometer) is used to identify the functional group in the chemical compound. Areas of good blue color in the Ukiyo-e contain Fe, which is the main element in ferric ferrocyanide. In the FT-IR spectra, the absorption peak of around 2090 cm^-1 corresponding to the CN triplet combination of ferric ferrocyanide (Fe₄[Fe(CN)₆]₃·xH₂O) is recognized. The Fe concentration in the faded blue area in the discolored sample is reduced to one-third that in the nondiscolored sample at the same position. The peak corresponding to the CN group has disappeared. A non discolored sample is subjected to accelerated ageing under the condition of high temperature and high humidity (353 K, 65%rh). The peak intensity of reflectivity in the aged sample decreases gradually with ageing.