Development of conservation procedures for late Edo period Japanese ceremonial dolls’ hair: Evaluation of effective treating reagents by using artificially degraded black-dyed silk fibres

Several procedures for conservation treatment were comparatively studied for degraded “ Suga- fibres” made of raw silk fibres dyed black. Two traditional methods, (1) neutralization with magnesium bicarbonate, and (2) antioxidant treatment with phytic acid, originally used for paper preservation, were tried for the conservation of Suga -fibres. The influences of a single treatment, or a combination of neutralization and antioxidant treatments, for the model fibres on their tensile strength were investigated under conditions of high humidity at high temperature before and after the accelerated aging test. The effect of the novel antioxidant cysteine on the fibre degradation was also examined. For the single treatments, the neutralization with magnesium bicarbonate retarded the degradation of higher iron-content iron (20%)/tannate-silk fibre, while the antioxidant with phytic acid treatment most effectively prevented the degradation of lower iron-content iron (2%)/tannate-silk fibre. This may be due to the different acidity in iron/tannate-silk fibres, and thus the degradation of iron (2%)/tannate-silk fibre would be caused by iron-catalyzed oxidation rather than acid-catalyzed hydrolysis because of its lower acidity. Among antioxidant treatments, cysteine more effectively retarded the degradation of the iron (20%)/tannate-silk fibre, while in the case of the iron (2%)/tannate-silk fibre, phytic acid more effectively conserved its strength and breaking strain. The result suggests that the thiol group of cysteine coordinates with an excess of ferrous ions in the iron (20%)/tannate-silk fibre and quenches the production of hydrogen peroxide. This study demonstrated that phytic acid, cysteine and magnesium bicarbonate treatments are useful as effective reagents for the conservation treatment of black-dyed textiles.