Spain. Pilar Roig, restorer, and Pilar Bosch, microbiologist, mother and daughter, have been using a bacteria-based restoration method for around fifteen years to clean stubborn glue from 18th century frescoes (see ill.) as well as traces of nitrate on wall paints and stone materials. Building on their success, the Spanish Ministry of Culture asked them, in 2021, in partnership with the University of Santiago de Compostela, to develop a non-toxic technique based on bacteria to remove graffiti in the urban space.
Several types of bacteria have already been ruled out by Pilar Bosch’s team, whose Bioxen scientific project focuses on the search for a microorganism that is neither toxic to buildings nor to human health, that is biosourced and environmentally friendly, for the specific restoration of stone heritage. Graffiti is difficult to remove because of its viscous, malleable material, which has a great capacity for penetration, particularly on porous surfaces such as rock. The physical and chemical techniques used to clean them often compromise the integrity of buildings, which biocleaning can remedy.
Conclusive results in the churches of Valencia
It was in 2008 that Pilar Bosch discovered a paper suggesting that bacteria, her field, could be used in the restoration of works of art and for frescoes in Italian churches, her mother’s area of expertise. After restoration missions of the frescoes of the monumental cemetery of Pisa and the frescoes of the Vatican Museums with the Italian scientific team of Colalucci and Giancarlo Ranalli, who have been working with bacteria since 2005, Pilar Bosch and her mother used their technique in Valencia (Spain), thanks to a research fund of four million euros, granted by the Hortensia Herrero foundation.
Bosch and Roig started with the frescoes of the church of Santos Juanes in 2013, where restorer Pilar Roig found herself in a bind. “Removing the glue manually from the frescoes would require several years of work,” she explains. Bacteria of the genus Pseudomonas stutzeriwhich produce natural glue-degrading enzymes, are mixed with a natural algae-based gel and spread over the paint, then removed after three hours. Remains undigested by bacteria are removed using a brush and water. “ The bacteria is non-toxic and does not harm the works, its use represents great potential for developing more environmentally friendly techniques.specifies Pilar Bosch. The duo has restored several buildings in the Valencian country with biocleaning, such as the San Nicolás Church in Valencia, the Serranos Bridge and the Trinity Bridge.
Research is progressing all over the world
The research carried out by the mother-daughter duo is innovative in Spain, but the use of bacteria to restore works of art has been developing in recent years in the international scientific community, particularly in Italy, following the example of the university of Ferrara where Elisabetta Caselli has been testing, since 2018, microorganisms to limit the biodegradation of oil paints caused by fungi.
Other promising research highlights the broad field of application of microorganisms, notably at New York University, where in 2021 Jason Horowitz developed a technique for restoring marble, with the bacteria Serratia ficaria (SH7), which feeds on fat and phosphate. In Switzerland, researchers at the Flexible Materials Laboratory are developing the BactoInk project, a bacteria-based ink that can be injected directly into a target site such as a crack in a vase or a chip in a statue, to repair the work and avoid further damage during the restoration process.
