E Richardson

Distribution of moisture in reconstructed oil paintings on canvas during absorption and drying : A neutron radiography and NMR study

Moisture is a driving factor in the long-term mechanical deterioration of canvas paintings, as well as for a number of physico–chemical degradation processes. Since the 1990s a number of publications have addressed the equilibrium hygroscopic uptake and the hygro-mechanical deformation of linen canvas, oil paint, animal glue, and ground paint. In order to visualise and quantify the dynamic behaviour of these materials combined in a painting mock-up or reconstruction, we have performed custom-designed experiments with neutron radiography and nuclear magnetic resonance (NMR) imaging. This paper reports how both techniques were used to obtain spatially and temporally resolved information on moisture content, during alternate exposure to high and low relative humidity, or in contact with liquids of varying water activities. We observed how the canvas, which is the dominant component in terms of volumetric moisture uptake, absorbs and dries rapidly, and, due to its low vapour resistance, allows for vapour transfer towards the ground layer. Moisture desorption was generally found to be faster than absorption. The presence of sizing glue leads to a local increase of moisture content. It was observed that lining a painting with an extra canvas results in a damping effect: i.e. absorption and drying are significantly slowed down. The results obtained by NMR are complementary to neutron radiography in that they allow accurate monitoring of water ingress in contact with a liquid reservoir. Quantitative results are in good agreement with adsorption isotherms. The findings can be used for risk analysis of paintings exposed to changing micro-climates or subjected to conservation treatments using water. Future studies addressing moisture-driven deformation of paintings can make use of the proposed experimental techniques.

Surface behaviour of PMMA: Is gel cleaning the way to go?

Introduction Poly(methyl methacrylate) (PMMA) has found extensive application in art and design since the 1930s (Waentig, 2008). Numerous artists have exploited its transparency through manipulating light and distorting the viewer’s perception. Consequently, preservation of these pristine, high-shine surfaces necessitates innovative cleaning strategies to avoid irreversible abrasion, particularly on aged PMMA. Although a comparatively stable polymer (Willcocks, 2002; Learner & Levin, 2014), the amorphous nature of PMMA makes it susceptible to penetration by solvents. Swelling during cleaning can lead to irreversible stress cracking and embrittlement (McGlinchey, 1993). We explore the use of aqueous polymer gel systems as a means of controlling solvent diffusion (Carretti et al., 2010; Cremonesi, 2010; Domingues et al., 2013) and reducing mechanical damage during treatment of PMMA (Balcar et al., 2012; Sun et al., 2014).