Abstracts - International Initiative for Georgian Cultural Studies

Giulia Caneva
University Roma Tre. Italy
Biodeterioration of Mural Paintings
The biological attack of the mural paintings of the church of the Virgin in Martvilli 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 (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 the
exception of the pink ones. These latter seem, in fact, to referred to other bacterial forms, with carotenoid
pigments, linked to high light input and lower values of humidity.
In general, the changes in biodeterioration appeared to be correlated mainly to light and to the air circulation,
especially 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 was carried out, using these organisms and their distribution as bioindicators.
Some conservation 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. Through a microclimatic evaluation of the site, 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.
Thomas Warsheid
LBW-Bioconsult. Germany
Biodeterioration on Wall-Paintings
The biodeteriorating effects of microorganisms on historical wall-paintings is based on a complex interaction
between building physiscs (i.e. humidity, temperature, ventilation), the type of historical materials
present (i.e. structure, thermal-hygric properties, nutritive effect) as well as the composition of the referring
microflora and their metabolic activity.
The deterioration of historical wall-paintings is basically determined by the porosity of the painted layer,
the stability of their mineralic respectively organic matrix, the absorption of moisture and humidity, the load
of soluble salts and the surrounding microclimatic conditions. Resulting damage processes are characterized
by salt efflorescence, swelling and detaching pigment layers as well as disintegrating corrosion leading
to powdering painting surfaces and the final loss of coherence of the wall paintings structure.
The described damage forms are often accompanied by microbial impacts such as the biogenic enrichment
of discolouring pigments (i.e. chlorophylls, melanins, carotinoids), the formation of moistureabsorbent,
swelling and sticky biofilms, the penetration and mechanical stress by fungal hyphae, the enzymatic
attack on organic substrates (i.e. historical binders, conservating consolidants) as well as the excretion of
organic acids.
Here, “Secco”-paintings are far more often victims of biodeterioration processes than “Fresco”-paintings
since they offer a wider range of organic subtrates (i.e. starch, glue, casein, oil, egg yolk), but even
anthropogenic influences can additionally support microbial deterioration processes by the increased deposition
of organic fine dust as well as the application of polymer consolidants in the course of restoration
treatments. Nevertheless the climatic conditions at site finally determine the extent of the potential microbial
endargement. The complexity of biodeterioration impacts on wall-paintings will be discussed based on
preliminary microbiological studies at the church of Ateni (Georgia) and related objects in Europe
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RESTORATION/CONSERVATION