DIFFERENTIAL EFFECTS OF TREATMENTS ON THE DYNAMICS OF BIOLOGICAL RECOLONISATION OF TRAVERTINE: CASE STUDY OF THE TIBER’S EMBANKMENTS (ROME, ITALY)

Monuments exposed to the environment are subject to numerous causes of degradation, including the action of biological organisms forming patinas and crusts of various colour and different aggressiveness. However, these patinas can be used in contemporary art for the creation of drawings, as in William Kentridge’s project, along the embankment of the Tiber River, illustrating the “Triumphs and Laments” of Rome history. More than eighty figures will be created through selective cleaning of the black biological patina on travertine, which is much used in Rome but little studied in biocide tests. The aim of this study is to understand which chemical treatments could delay the biological growth in the cleaned area, extending the lifetime of the images. Three commercial biocides (Algophase®, Biotin R®, Preventol R80®) and two water-repellents (Hydrophase superfici®, Silo 111®) were chosen and tested in situ (30 tests areas, with three repletion) using different concentrations and mixtures, in accord with the safety of users and environment. In order to limit the re-colonization after treatments, colour measurements and portable optical microscope were conducted both on the bare surface of the stone (the control test) and on the stone after chemical treatments.The results show that each product has different biocidal efficacy and a different colorimetric response. The preventive treatment of Preventol R80® with subsequent application of biocides in mixture had the best results in preventing re-colonisation. The use of water repellents alone was revealed to be ineffective in preventing biological recolonization and also determined colorimetric alterations in terms of brightness.The experimental data has provided an improved understanding of the effects of chemical treatments on travertine and of the phenomena of biological recolonization dynamics.