In the early 1980s, Professor Richard Wolbers of the University of Delaware Program in Art Conservation developed a cleaning system using chemically modified gels to clean the surfaces of paintings and other objects. The gels allowed more control over cleaning than did traditional solvent systems, and they were far less toxic. In the last several years, some conservators and conservation scientists have raised important questions regarding the amount of residue left by gels and the potential role of the residue in any later deterioration of the cleaned surface.
To answer some of these questions, the GCI developed a research project with scientists at the University of Delaware Program and the Winterthur Museum, and Getty Museum conservators. To address the qualitative identification of surface residues and quantitative assessment of the amount of surface residue after cleaning with a gels system, the GCI collaborated with Professor David Miller of the Department of Chemistry at California State University, Northridge, to develop a highly sensitive analytical methodology using radioactive-labeled materials. The methodology involved a cleaning experiment using four chemically identical mixtures of a gel formulation—each with one of its major components radioactively labeled with tritium or carbon 14—and the analysis of all cotton swabs used in gel application and removal, as well as of the sacrificial painting samples. This study offered a fuller understanding of the cleaning process and provided data on the rate of removal of gel from the painted surface, as well as on the amount and type of gel residue.
Because the cleaning process differs from one conservator to another, in order to obtain realistic and useful data, the GCI invited a group of conservators to participate in an experiment to assess variations in individual cleaning techniques. Leading scientists who have researched other aspects of these cleaning systems were invited to contribute to the experiment, which took place during the first week of November 1998.
Experiment participants included Aviva Burnstock, Courtauld Institute of Art, London; Johann Koller, Doerner Institut, Munich; Katharina Walch, Bayerisches Landesamt für Denkmalpflege, Munich; Paolo Cremonesi and Roberto Bellucci, Opificio delle Pietre Dure e Laboratori di Restauro, Florence; Joe Fronek, Los Angeles County Museum of Art; Chris Stavroudis, a conservator in private practice; and Mark Leonard, of the Getty Museum.
Interpretation of the scientific data obtained from the more than six hundred samples generated by the conservators during the experiment and the notes taken on each conservator's technique will help to answer crucial questions regarding gel residues. The results will be shared with participants, and an exhaustive interpretation of the results will be published in peer-reviewed conservation journals.
General conclusions can be drawn from the preliminary data. The amount of surface residue after cleaning with the gel is very low for components of higher molecular weight and boiling points. The low-molecular components (e.g., isopropyl alcohol) evaporated quickly to below detection limits within hours, as expected. Also, differences in the techniques of individual conservators did not exceed a factor of 2-3. Surprisingly, extensive solvent cleaning did not substantially improve cleaning efficacy. And it appears that a cleaning with dry swabs followed by several wet swabs resulted in the least residue. The study's results will guide a recommendation for an optimum cleaning procedure.
Gathering the collective experiences of scientists and conservators representing national and international institutions offers an effective way to conduct studies on critical issues in conservation, and this methodology contributed to the success of this phase of the gels research project. A next step will be to study for signs of deterioration on the surface of paintings and objects cleaned over the last 10 years using the gel systems, and to ascertain if components of gel residue, albeit low, could be a factor in any change.