Cleaning Wall Paintings: methodological approach with low chemical risk

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Prof. M. Coladonato, A. Marra, and participants of the workshop at the Department studios. Image courtesy of Ajda Mladenovič.

Review by Neva Pološki and Barbara Horvat Kavazović

This workshop was organized by and held at the Department for Conservation and Restoration of Works of Art (The Academy of Fine Arts, University of Zagreb) in Zagreb, Croatia from the 24th until the 28th of September 2018. The workshop was led by Prof. Maurizio Coladonato (he teaches at Istituto Superiore per la Conservazione ed il Restauro (ISCR), Academy of Fine Arts Naples and Academy of Fine Arts of L'Aquila) and Art Conservator Annalisa Marra (she holds a degree in science of cultural heritage from University of Salerno and completed her training in the restoration of mural paintings and canvases at ISCR in Rome).

Within the last few years the Department's initiative to expose students and professionals to the most recent advances and practices in the field of cultural heritage preservation, with experts sharing their rich experience first-hand, has resulted in successful collaborations and numerous visits with prominent lecturers from Austria, Germany, Italy, Slovenia, Poland, and Australia. This initiative has been recognized by the International Trust for Croatian Monuments. The Trust was founded in 1991 and is dedicated to raising funds and supporting the preservation of cultural heritage in Croatia as well as helping with the education of young Croatian conservators. Thanks to the Trust, this workshop was made possible.

Participants included students and professors from the Department, independent Croatian conservators, and conservators and scientists from the Croatian Conservation Institute, Institute for the Protection of Cultural Heritage of Slovenia, and The Suor Orsola Benincasa University of Naples (Italy). The five-day workshop included theoretical lectures and practical work in the conservation studios of the Department as well as practical work on the wall paintings in situ in the Brezovica castle near Zagreb. The theoretical part of the workshop started with lectures on the most recent European regulations for safe storage, utilization and deposition of dangerous and toxic materials, and adequate personal and work environment protection. Prof. M. Coladonato presented the TriSolv application developed by himself and Prof. Scarpitti (ISCR). This free web-based Flash application, based on the Teas Chart (a solubility diagram), was recognized as an extremely useful tool during every stage of the conservation process—cleaning, removing damaged/altered materials, application of coatings, etc. The organized and interactive system facilitates the understanding of complex solubility behaviors allowing conservators to shift from toxic solvents to less hazardous ones while maintaining the same efficiency. The lecture provided the theoretical foundation of solubility parameters and was followed by practical training using the TriSolv application. Further lectures focused on materials which are used in the field of wall paintings conservation, primarily for surface cleaning and desalination. Treatments for wall paintings often include cleaning with water-based solutions made with a variety of reagents as well as inert materials used to apply the solutions via poulticing techniques. The additives often used in these solutions include ammonium carbonate, ammonium bicarbonate, EDTA disodium salt, and triammonium citrate; these materials were covered individually in order for participants to fully understand their chemistry and characteristics.

A section of the lectures examined the conductivity and solubility of the ionic compounds as well as the use of water solutions containing CO2 for the removal of calcareous concretions. The theoretical portion of this workshop was concluded with a lecture on using hydrogen peroxide as a cleaning agent and the chemistry of ionic exchange resins and surfactants' characteristics, which are especially important for the preparation of gels as an alternative for cleaning painted surfaces.

The practical part of the workshop in the Department's conservation studios was led by Prof. M. Coladonato and accompanied by A. Marra. They demonstrated the methodology of measuring the pH and conductivity of prepared water-based solutions and wall painting surfaces by using agarose plugs. Through this demonstration, the participants developed a more acute awareness of these concepts, highly important for defining the intrinsic properties of solutions and modulating their cleaning effectiveness according to the surface properties. By sharing their experiences in formulating, producing, and applying the aforementioned materials and cleaning systems during numerous wall painting conservation projects, the lecturers sparked a spirited discussion with the participants who were eager to share their own experiences and different approaches to dealing with similar problems they had encountered. The participants were also introduced to the appropriate preparation of these cleaning systems, which included solvent mixtures determined using the TriSolv application and several gelling materials (Gellano Kalcogel®, Klucel® G and Carbopol® EZ-2), which were later used on the wall paintings in the Brezovica castle.

The last day of the workshop was held in the Brezovica castle, a representative example of profane architecture of the Baroque period in continental Croatia, which includes wall paintings from the 18th century. The abandoned castle has suffered many unfortunate brake-ins and vandal attacks which, on several occasions, resulted with the wall paintings being sprayed over with graffiti, the last attack occurring as recently as the spring of 2018. As the graffiti ages, the spray paint has become increasingly difficult to remove. This is a problem the Department has been battling with for the last couple of years, so one of the missions of the workshop was to formulate the appropriate cleaning system for its removal. Cleaning trials were conducted with the aforementioned materials prepared in the Department's conservation studio, and the results were discussed among the participants. Certain formulations of gels proved to be very efficient, demonstrating how mixtures of nontoxic solvents with prolonged action can effectively remove aged synthetic paint from porous surfaces.

The workshop ended in high spirits to the satisfaction of both the participants and lecturers. This was due in part to the promising cleaning results obtained working in situ, which defined a new approach in resolving an old issue. Also, the workshop ended with a mutual desire by all to continue sharing knowledge and experiences through future collaboration.


Neva Pološki earned a master's degree in conservation at the Academy of Fine Arts and Design, University of Ljubljana, with a dissertation on aesthetic reintegration of wall paintings in Croatia. From 1997 until 2012 she worked at the Croatian Conservation Institute as a wall painting conservator, and in 2012 she started teaching at the Academy of Fine Arts in Zagreb as an assistant professor.

Barbara Horvat Kavazović graduated at the Department for Conservation and Restoration of Works of Art at the Academy of Fine Arts in Zagreb. Since 2010 she has worked at the Department, first as a teaching assistant and now as an assistant professor, specializing in easel paintings and cleaning processes. She is pursuing a PhD in the field of preservation of cultural heritage.

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