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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).

Substituted substance(s)

  1. EDTA (ethylenediaminetetraacetic acid)

    CAS No. 60-00-4 EC No. 200-449-4 Index No. 607-429-00-8
  2. Ammonium carbonate

    CAS No. 10361-29-2 EC No. 233-786-0 Index No. 
  3. Potassium hydroxide

    CAS No. 1310-58-3 EC No. 215-181-3 Index No. 019-002-00-8

Other type of alternative

Bacterial suspension

Reliability of information

Evidence of implementation: there is evidence that the solution was implemented and in use at time of publication

Hazard assessment

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.

» Check the Substance Database according to SUBSPORT Screening Criteria (SDSC)

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Substitution description

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.

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Case/substitution evaluation

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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Other solutions

Further information

You will find more information here (article in spanish): PDF

Further languages available

Who provided the information

Type of information supplier


Rosa María Montes                                                                                                                                                                                                           Pilar Bosch Roig                                                                                                                                                                                                      Polytechnic University of Valencia (Spain)                                                                                                         

Publication source

National Geographic (2012) Kleine Helfer in der Kirche. 1 (2012), S. 29

Type of publication and availability 

Original document: click here

Comments from SUBSPORT users

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