The Use of Menthol as Temporary Consolidant in the Excavation of Qin Shihuang's Terracotta Army

Temporary consolidation is widely used to protect delicate artefacts or other fragile relics in art conservation. Although cyclododecane is extensively accepted, the safety-related issues have become an increasing concern and its short working time is always annoying. Inspired by its low melting point, polar structure, well-established safety profile, easy local availability and low cost, we propose menthol as a new temporary consolidant on the new excavation site of Qin Shihuang's Terracotta Army. In this paper, we offer a preliminarily exploration of the kinetics of menthol sublimation on two different matrices, its residue after volatilization, its penetrability and distribution in simulated terracotta samples, as well as other important properties in the laboratory. The results obtained from these tests reveal that the sublimation of menthol can be a zero- or a first-order process, depending on the porosity of the matrices, and its best operational temperature resides in the range of 60–80°C. Finally, two field cases at the archaeological site of Qin Shihuang's Terracotta Army are presented to show that menthol is a very effective temporary consolidant.