Delamination Due to Zinc Soap Formation in an Oil Painting by Piet Mondrian (1872-1944) Conservation Issues and Possible Implications for Treatment

The privately owned oil painting Composition with Color Planes 4 (1917) by Piet Mondrian (1872–1944) has been the subject of ongoing investigation since 2011. The painting consists of color planes in a field of differing whites. Some~of these white areas suffer from delamination issues, in combination with flaking. Previous research demonstrated a link between the presence of zinc oxide and the delamination phenomena. More recently, the formation of zinc soaps was found to play a role. In this study, cross sections from both delaminating and relatively intact white areas were investigated with light microscopy, SEM-EDX, and ATR-FTIR imaging to obtain more information about the stratigraphy and condition of the paint layers. Two stages in metal soap formation were identified in the delaminating areas. The first stage consists of noncrystalline zinc soaps or zinc ions bound to carboxylate functional groups in the polymerized oil network. Crystalline zinc soaps, which represent the second, final stage of metal soap formation, are generally linked to the development of zinc soap related deterioration phenomena. In this case, they were found at the interface between the delaminating paint layers. Possible implications for treatment and factors that might trigger further delamination will be discussed.