The Restoration of the Largest Archaelogical Discovery—a Chemical Problem: Conservation of the Polychromy of the Chinese Terracotta Army in Lintong

Abstract

The conservation of the polychromy of the terracotta army of the first Chinese emperor Qin Shihuangdi represents a special problem because of the deterioration of the ground layer consisting of organic material. This was triggered due to it having spent more than 2200 years in water-saturated soil. The consolidation of the polychromy was achieved through polymerisation of a specially adapted combination of monomers.

Polymerization mechanism of natural lacquer sap with special phase structure

“…The lacquer sap obtained from Rhus vernicifera lacquer tree mainly consists of urushiol (60–65%), water (20–30%), lacquer polysaccharide (3–7%), water-insoluble glycoprotein (~ 1–2%), laccase (~ 0.2%) and stellacyanin (~ 0.02%) 2 – 4 . In China, Japan and other Asian countries, it has been used as a coating material for several thousand years 5 , 6 . Unlike the drying of traditional synthetic coatings by solvent evaporation, lacquer film, which is a highly cross-linked three-dimensional polymer, is formed by the oxidation polymerization of urushiol monomer catalyzed by laccase under high humidity 2 , 7 – 11 .…”

Laccase‐catalyzed polymerization drying of Chinese lacquer sap with TiO2 nanoparticles

“…An autoxidation of urushiol also occurs on the unsaturated side chains in the presence of air, but it is very slow . The complex components of lacquer sap and its unique film‐forming mechanism endow the lacquer film with excellent performances such as high thermo‐stability, water impermeability, insulating quality, super‐durability, and good corrosion resistance . So far, no artificial paints or coatings are better than the lacquer sap on the comprehensive performance.…”

“…1,5,6 The complex components of lacquer sap and its unique film-forming mechanism endow the lacquer film with excellent performances such as high thermo-stability, water impermeability, insulating quality, super-durability, and good corrosion resistance. 7,8 So far, no artificial paints or coatings are better than the lacquer sap on the comprehensive performance. However, as a kind of coating, lacquer sap is mainly used in indoor environment or on the inner surfaces of pipelines because lacquer film is not resistant to ultraviolet rays.…”

Synthesis and properties of thermosetting resin based on urushiol

“…1,2 It is reported that lacquer was used as a durable coating material in China thousands of years ago. 3 Such a renewable coating exhibits beauty, extraordinary durability and high gloss with an environmentally friendly enzyme-catalyzed curing process at room temperature. Urushiol is the main component of Chinese and Japanese lacquer.…”