Cholesteric liquid crystals as weathering indicators for marble surfaces

Cholesteric liquid crystals have been used to study the weathered surfaces of marble from the Sanctuary of Demeter in Eleusis, near Athens. Previous i nvestigations have shown that when a cholesteric phase is spread across the surface of the stone, the pitch of the mesophase is sensitive to the topog raphy of the surface. The wavelength of the maximum in the reflected spectr um varies therefore with the microtexture of the surface. Small samples of surface stone from the temple which had been weathered in distinctive ways, were investigated in the laboratory. There appears to be a significant cor relation between the optical reflectance spectra and the surface microtopog raphy investigated by SEM, as indicated by computer aided analysis (Digital Image Processing). The results point to the development of an effective in situ method of monitoring the weathering of marble surfaces using choleste ric liquid crystals.