Damaged aspect of lining paper on silk-based painting by Rokusho-Yake (malachite burning)

Abstract

The versos of aged silk-based painting (Kenpon), especially in the green and blue areas, indicate serious damage changing the color to bark, and the texture to brick texture (Rokusho-Yake). It is well known that Cu, from green and blue pigments, are caused by this damage. These damages have been observed to also extend to lining papers. Herein, two layers of lining papers damaged by Rokusho-Yake removed in the process of conservation from the verso of Kenpon painted ca.600 years ago were used for analyses. The results showed that the molecular weight of cellulose in the lining papers damaged by Rokusho-Yake was lower than that of slightly damaged lining papers in the unpainted area. Elemental analysis detected large amounts of Cu in the lining papers damaged by Rokusho-Yake. Depending on the amounts of Cu present in the samples, it is suggested that Cu diffused and moved to the verso from the recto, where the pigments are painted, through the two lining papers. Moreover, Cu was detected in the blotting paper used during water cleaning process in conservation, showing that a part of Cu is hydrosoluble. By the analysis of Gel Permiation Chromatography Cu ions were considered to accelerate the decrease in the molecular weight of cellulose in the lining paper.