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Sample 3 surface after biocleaning. (a) Portable microscope observation on site: surface from the biocleaned area showing rather homogeneous results. Arrow 1, clean area; arrow 2, traces of residual layer of dirt. (b) SEM observation, showing a homogeneous smooth surface. Arrow 1, small microcracks; arrow 2, a few incoherent crystals on the surface. (c) SEM observation of a polished cross section. The arrows indicate the presence of the yellow-ochre layer (patina) in the whole section.
