Corrosion of ancient marble monuments by rain: Evaluation of pre-industrial recession rates by laboratory simulations

By a multiple series of laboratory simulations of rain runoff on marble tiles it was possible to obtain a semi-quantitative evaluation of pre-industrial recession rates for marble surfaces exposed to weathering. The approximate value of 0.03–0.05 mm per century was established for partially sheltered vertical surfaces. The lower value refers to climatic conditions typical of Rome whereas the higher value relates to more severe climatic conditions (heavier rainfalls and/or lower rain intensities). Even higher values, that is, 0.15–0.25 mm per century (always to be intended as approximate) can be obtained for fully exposed and inclined marble surfaces. These data were compared to the recession rates obtained by other scholars, especially relating to tombstone studies: a certain agreement was found only for the lower values reported. On this basis a revision of the methodologies and an interpretation of the divergencies are proposed.