NATIONAL PHD IN HERITAGE SCIENCE

Thesis title: Multi-analytical study of the physical and chemical aspects at the interface between oil paint films and acrylic-based grounds in contemporary paintings.

The use of oil paint on ready-to-use acrylic primed commercial canvases is a common practice, offering versatility and fast-drying times. However, the interaction between these layers remains insufficiently understood, particularly at their interface. While acrylic grounds are appreciated for their rapid drying and flexible nature, they have been reported to cause delamination and degradation in some instances, raising concerns about their long-term stability when combined with oil-based paints. Defects such as wrinkles, protrusions, cracks and delamination associated with modern and contemporary oil paintings still present the greatest challenges. However, the existing literature on these conservation issues remains scarce. The objective of this study is, therefore, to study the processes and mechanisms taking place at the interface between oil paint films and acrylic-based grounds. For this purpose, the research was divided into two parts: the first part focused on the study of film formation processes and degradation stages of pictorial layers; in the second part, special attention was paid to the failure mechanisms taking place at the interface between oil paint films and acrylic-based grounds. In the first phase, the research provided a deeper understanding of the interaction at the interface between the pictorial layers. A multi-analytical approach combining empirical tests (scribe tests), spectroscopic (ATR-FTIR), thermal (TG-DSC), chromatographic (GC-MS), and advanced imaging techniques (FESEM-EDX and IMS-DESI-MS) enabled the mapping of organic and inorganic components and the detection of both vertical and transverse metal ion migration. Key findings revealed that metal ions can migrate, catalysing the drying kinetics, altering the reactivity, and inducing structural changes in adjacent oil-paint films, thereby promoting the propagation of cracks, delamination, and protrusions. In the second phase, the research has led to the identification, localisation and characterisation of early degradation phenomena such as cracks, protrusions and opacity, across the entire stratigraphy, even before they become visible to the naked eye. Multiband imaging (MBI) coupled with ATR-FTIR, GC-MS and FESEM-EDX, suggests that the choice of ground significantly influences the surface. Additionally, mechanical testing revealed how physical stresses—such as tension and environmental factors—affect the structural integrity of the layers over time according to the pictorial structure. Results suggested that, beyond the interface issues between the acrylic ground and the oil paint layer, the compatibility of additives may also play a crucial role. The results obtained and the methodologies developed in both phases of the research were then applied to real case studies. Close collaboration with conservators turned out to be necessary to develop a more complete understanding of the phenomena observed experimentally in the laboratory. The research provided informed guidance to artists on the appropriate selection and combination of materials and, secondly, a comprehensive methodology for the development of scientifically supported preventive conservation strategies for contemporary paintings.