AIC's 45th Annual Meeting

The recent introduction of rigid or semi-rigid gels (gellan gum, agarose, agar, xanthan gum etc.) to the field of paper conservation opened new possibilities for treatments, especially for local cleaning. Such gels can be used with aqueous cleaning systems optimized via pH and conductivity adjustment and through the addition of buffers, chelating agents or antioxidants. To the best of our knowledge, parameters including chemical additives as well as the long-term consequences of such treatments remain open questions. Those questions are particularly important regarding local cleaning of stained artworks, due to the tendency of rigid gels to create a new wet/dry interface (or tideline) during treatment. A first investigation was started in 2015, in collaboration with the CRC (Centre de Recherche sur la Conservation des Collections, Paris) during a master's thesis research. The study was devoted to the specific use of agarose gel with adjusted pH and conductivity for local treatment of tidelines on paper. Tidelines were created on samples of artificially aged Arches® paper. Different combinations of pH and conductivity were tested to evaluate which are best for cleaning. It appears that alkaline pH and high conductivity were efficient for the cleaning of tidelines on the samples. Nevertheless, comparison with other solutions used to prepare the gels showed that calcium hydroxide solution is best for the cleaning of tidelines. The long-term effect of local treatments was also investigated using hygrothermal ageing of the cleaned samples. Despite the use of cyclomethicone solvents and pre-humidification to limit the diffusion of water, UV fluorescence was observed. This resulted from the creation of a second wet/dry interface during treatment. Fluorophores being precursors of colored compounds, this result emphasizes that local cleaning should be approached with caution. A "sandwich” configuration was also tested, by applying on one side of the sample the agarose gel prepared with a calcium hydroxide solution to clean locally the tideline and on the other side gellan gum covering the whole sample surface. This configuration showed promising results in terms of cleaning, aging and avoiding the creation of a second wet/dry interface during treatment. This sandwich method is nevertheless only applicable to artworks that can be wetted on their entire surface. The research will be continued starting in the fall of 2016 at the Smithsonian American Art Museum, and will be dedicated to the use of rigid gels and the optimization of the aqueous systems for local treatment of stained artworks on paper with water-sensitive media. Colorimetry measurements will be used to determine the cleaning efficacy of different gels made with buffers, chelating agents and antioxidants. The long-term consequences of those chemical agents, coupled with local cleaning will be evaluated by using artificial aging. As previous research has shown that local treatment can lead to unwanted long-term effects, new solutions will be tried to avoid formation of tidelines such as using an interface made of paper or applying cyclododecane. The paper's surface will be examined using optical microscopy. The first results of this research will be presented here.