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

Abstract

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.

Studies of internal stress induced by solidification of menthol melt as temporary consolidant in archaeological excavations using resistance strain gauge method

“…Meanwhile, the other strain gauge on the bottom of glass provides positive values which suggest tensile deformation. It is known that solidi cation of menthol melt is accompanied by volumetric shrinkage 24 , which leads to concave bending of the glass I sample in the present experiment. This bending results in compression and stretching, respectively, in the upper and lower portion of glass, in consistent with the measurements of strain gauges.…”

“…Cyclododecane (CDD) [14][15][16][17][18][19][20][21] and menthol [22][23][24][25] , also referred as "volatile binder media" [23][24] , are mostly used temporary consolidants. In typical applications, the material is melted and applied on the target cultural relics.…”

“…Thus, it arouses our attention and interest in investigating possible internal stress induced on the artifacts during temporary consolidation practice. Although successful applications of CDD and menthol as consolidant have demonstrated their safety to cultural heritages [14][15][16][17][18][19][20][21][22][23][24][25] , vital information about the internal stress such as generation mechanism, magnitude and distribution, which can be interesting and helpful to conservators, is still unclear.…”

Temporary consolidation and packaging of fragile cultural relics at underwater archaeological sites to maintain their original state during extraction

“…On land archaeological sites, cyclododecane (Rowe and Rozeik 2008;Brown and Davidson 2010;Vernez et al 2011) and menthol (Han et al 2014(Han et al , 2016(Han et al , 2018, both solid materials that can be removed by sublimation, are primarily used to reinforce unearthed relics temporarily and ensure their safe transfer. However, these materials cannot be applied to underwater archaeological sites.…”

Application of veratraldehyde as a temporary consolidant for relics at underwater cultural heritage sites

“…More recently, Han et al . (, , ) found better performance for menthol as a temporary consolidant material, which led to a major innovation in the development of such materials. These fit into a notable development of temporary consolidant materials for use at archaeological sites on land.…”