The cleaning of old frescoes with a bacterial suspension
This case story presents the use of Pseudomonas stutzeri for the biocleaning of mural paintings, for the purpose of eliminating remains of organic material from old restorations or insoluble saline efflorescence. Traditional techniques used in cleaning involve: solvents, spirits, alkalis, acids and soaps, as well as simple mechanical actions (ex. scraping with a scalpel).
The restoration agent is a mixture containing substituted substances and may cause irritation to skin and eyes. The bacterial suspensions show usually no chemical hazards.
The frescoes in the Church of Santos Juanes in Valencia, Spain, were damaged by fire in 1936 and improperly restored in the 1960s and from salt blooms (a side effect of pigeon nests). Researchers at the Institute of Heritage Restoration and the Centre for Advanced Food Microbiology from the Polytechnic University of Valencia (Spain) had an idea to use the harmless Pseudomonas bacteria to clean the works instead of toxic chemicals.
Pseudomonas stutzeri bacteria were developed by a team of biologists, who taught the group that cleaned the Campo Santo di Pisa in Italy from practical knowledge.
Effectively trained to eat salt and glue, the bacteria are brushed onto the frescoes and covered with a gel that, when heated with lights, creates perfect conditions and aids cleanup. Just 90 minutes later, the targeted area of the fresco is washed clean with water and dried, killing the bacteria and leaving behind a shiny clean section to admire.
In the past, to remove foreign materials encrusted on ancient artworks restorers used reactive chemicals that are non-selective and toxic. Or they tried to wear away the crust by mechanical means, which is time consuming and can damage the paint.
In this way, about one third of the frescoes decorating the walls of the baroque and gothic Church, whose original structure dates back to the 13th century, have been restored to date.
The alkaline agents for restoration of old frescoes can be substituted by non-chemical alternative. It is a bacterial suspension and contains leaving microorganisms. They are selected for these processes and are not sporulating and non-pathogenic, so they do not generate a risk to workers.
According to the research publication from Pilar Bosch Roig the biocleaning is favorable from a health and environmental point of view. The SUBSPORT team is not aware of potential disadvantages with the method described.
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Rosa María Montes Pilar Bosch Roig Polytechnic University of Valencia (Spain) email@example.com
National Geographic (2012) Kleine Helfer in der Kirche. 1 (2012), S. 29Type of publication and availability
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