Biodeterioration of mural paintings in the Church of the Virgin in Martvili (Georgia)

The biological attack of the mural paintings of the church of the Virgin in Martvili was analysed, with a floristic and ecological approach. This problem was particularly relevant in the case of the western porch of the church, where diffuse growths of blackish, green and pink patinas, due to cyanobacteria (Chroococcales) and other bacterial forms were detected. These biological colonisations were studied through optical microscopy and SEM, and differences between the different phenomenologies appeared mainly quantitative, with exception of the pink ones. These latter seem in fact to be referred to other bacterial forms, with carotenoid pigments, linked to high light input and lower values of humidity. In general, the changes in biodeterioration appear to be correlated mainly to light and air circulation, especially to the direction of humid air and fog during winter. Considering the porosity of the materials (mortars and stone) and the different environmental conditions in the porch, a map of the humidity level of the walls has been developed, using these organisms and their distribution as bioindicators. Some conservative treatments were carried out with preliminary tests of efficiency, using two biocides (Rocima 110 and Preventol R80, quaternary ammonium salts, in the first case plus an organotin compound) widely tested and used in the past. Further interventions of environmental conditioning were also suggested, in order to limit the ecological ability of these organisms to grow, and solve this problem in a long lasting way