LAUSR

Abstract In this work, we review recent studies on zinc saponification mechanisms, which occur as degradation products in modern oil paintings and severely affect the cohesion of pictorial layers. The issue has gained great attention in the last decades, when research moved from the mere phenomenon observation to the understating of the critical behaviour of zinc oxide in an oleic matrix. The structure formed by the two paint constituents, i.e. drying oil (polymeric matrix) and pigment (suspended solid particles), demonstrated to represent a fundamental aspect for the instability of the paint film and its ageing showed important analogies with degradation of commercial ionomer networks. The complexity of the system and the cultural value of the investigated objects has posed great challenges and has required the collaboration between physicists, chemists and conservation scientists to answer both applied and fundamental questions related to this conservative issue. As the research has now reached maturity, this review conveys the acquired knowledge on this topic, summarizing and illustrating the main phases of evolution of the zinc oxide-binder system, corresponding to pigment dispersion and dissolution, formation of the ionomer network and crystallization of metal soaps. The final scope of this work is to guide and pave the way for future studies related to this issue and facing similar problematics.