Nicoletta Barbabietola*, Chiara Alisi*, Flavia Tasso*, Michela Grimaldi*, Salvatore Chiavarini*, Carla Ubaldi*, Paola Marconi*, Brunella Perito**, Anna Rosa Sprocati* * ENEA Casaccia, Rome, Italy (
** University of Florence, Italy
Abstract
The use of biotechnology is quite well developed in many fields, whereas in the art and restoration domain it is scantly applied. In this field biotechnological procedures could be useful to integrate rather than replace conventional chemical-physical restoration procedures, when these are ineffective or toxic for end-users and for the environment. Microorganisms, which are usuallyrelated to biodeterioration, can represent, on the other hand, a source for the development of new biotechnological solutions for restoration and conservation. In the present paper the use of selected bacterial strains for the removal of shellac resin from artworks’ surfaces was investigated. Shellac, a natural organic resin of animal origin, has been largely used as a fixative for wall paintings, due to its good penetration and adhesion features; when exposed to environmental factors it loses its elasticity and mechanical strength and, by ageing, it becomes hard and insoluble, making the painting matt. The traditional cleaning procedures are ineffective in the removal of aged shellac, as is well documented by the case of the Ajanta caves. In this case a biological approach could usefully integrate the chemical procedures to complete the removal without damaging both the artwork as the operators safety. Tirthytwo
strains, isolated from the Etruscan tomb of Tarquinia or from contaminated environmental matrices, were selected for their capacity of oxidizing shellac as substrate, by means of BIOLOG TM system methodology. Three of these strains showed to be the most effective and were tested for the capability to use the target substrate as sole carbon source: CONC 11 (Pseudomonas stutzeri), CONC 18 (Achromobacter xylosoxidans ) and LAM 21 ( Acinetobacter calcoaceticus). To check the effectiveness of the shellac degradation and the presence of undesired by-products, the microbial transformation of shellac resin was monitored by GC-MS. GC-MS analyses identified butolic acid as a marker for the molecular pattern recognition of the resin. Gas-mass analyses showed variations in shellac composition after 1 day of incubation with the selected
strains and, after 3 days, the concentration of butolic acid was reduced by more than 80%, in correspondence to the plateau of the growth curve. Work is in progress to understand if other components of shellac are also undergoing microbial transformation. To carry out in vivo tests for bio-removal of aged shellac, specimens of wall paintings were purposely prepared, spreading three different pigments (kaolin, cinnabar and indigo) diluted inthree organic media (rabbit glue, linseed oil and arabic gum) over a thin plaster layer. Specimens
were then incubated in a climatic chamber with 96% R.H. and 34°C, to simulate climatic conditions similar to Ajanta caves. At the end of the weathering period, specimens will be treated with a bacterial suspension in order to check its capability to remove the shellac film. Bacterial strains will be tested in different combinations and successions, in order to develop tailor-made microbial formulas and procedures, for specific restoration requirements.
{flippingbook_book 26}