Two methods for the conservation of the polychromy of the terracotta army of Qin Shihuang: electron beam polymerization of methacrylic monomers and consolidation using polyethylene glycol

Abstract

The life-size sculptures of the terracotta army of the first Chinese emperor, Qin Shihuang, are among the most famous archaeological monuments in the world. The site, located in Lintong, about 45 km northeast of Xi'an, is still being excavated. Rows of soldiers are on display in the site museum. The sculptures, gray-brown in color, originally were painted vividly, then buried for 2,200 years in humid soil. Soon after excavation and exposure to a dry environment, the polychromy of the terracotta sculptures flaked off rapidly as water was lost from the ground layer, which is made of East Asian qi-lacquer. For this reason, after excavation and before conservation begins on other terracotta pieces, the objects are maintained in a humid environment to prevent detachment of the paint layer. The authors' project concerns the development and testing of special conservation methods to preserve the polychromy of the terracotta army. This work is being carried out in both Germany and China. The problem facing conservation of the terracotta figures is stabilizing the lacquer layer in such a way that it no longer shrinks when it loses water. None of the substances usually used for restoration give positive results. This report discusses two new strategies that have been developed for conserving the polychromy: polyethylene glycol (PEG) consolidation and electron beam polymerization of 2-hydroxyethyl methacrylate (HEMA). Both PEG consolidation and electron beam polymerization have proven capability to serve the conservation needs of the terracotta army. Both have clear advantages, but each also has room for improvement.