Removal of Bats’ Excreta from Water-Soluble Wall Paintings Using Temporary Hydrophobic Coating

Abstract

ABSTRACT The removal of bats’ excreta from the decorative surfaces of India’s Ajanta cave (2nd BCE to 5th CE) was always feared due to the water solubility of the plaster and the binding glue in the paint layer. Although the caves are now free from bats, their heavy discharge in the past is having a telling impact in the form of damage to painted plasters and basaltic rock surfaces. Studies undertaken through FTIR, Raman spectroscopy, SEM-EDS, ion strip tests, etc. showed guano seeped deep into the earthen support through the paint layer. In the present work Cyclododecane (CDD), a volatile binder and reversible consolidant, was utilized to protect the infested paint layer from any water ingress and the surface was successfully cleaned with phytagel and de-ionized water. The two-step process cleaned guano from water-sensitive painted surfaces by selective masking with CDD which sublimed in few months leaving no visual residues on the substrate. This hydrophobic process of cleaning is certainly advantageous to other aqueous methods that may cause damage to the proteinaceous binder, found mixed in the paint and earthen plaster layers at Ajanta. The process can now be successfully applied to similar other sites in India and elsewhere for guano removal.