Laboratory Research into the Use of Menthol as a Temporary Consolidant for Conservation on Archaeological Excavations

Due to its ability to evaporate completely at room temperature, menthol has recently been proposed for use as a new kind of temporary consolidant at the excavation site of Qin Shihuang's Terracotta Army. Compared to cyclododecane (CDD), the most widely used temporary consolidant, menthol has the advantages of a longer working time, a well-established safety profile and easy local availability. In this paper, in order to better understand the temporary consolidation behaviour of menthol and to guide its optimal use in the field, laboratory experiments are carried out on ISO standard sand substrate in conditions mimicking the situation of an archaeological excavation. Basic and important knowledge about menthol, which is related to its effectiveness in temporary consolidation, such as penetration into the substrates, the solidification process and the degradation of the efficiency of consolidation over the sublimation time, are systematically studied. The results show that the penetration of menthol is notably affected by the substrate's temperature, particle size, particle-size distribution and water content. The solidification of melted menthol is an obvious volume shrinkage process, and the shrinkage extent is greatly affected by the application protocol. The consolidated samples experience a dramatic promotion in compressive strength, and as menthol volatilizes, the consolidated samples will eventually become loose and finally collapse.