Chemical Aspects Influencing Crack Formation in Black-and-White Oil-Based Paints: Study of Five Spanish Abstract Informalist Paintings by Antonio Saura (1930–1998)

This study explores the chemical and physical mechanisms behind the distinct cracking patterns observed in the black-painted areas of five works by Antonio Saura, a key figure in 20th-century Spanish Informalist art. The investigation is prompted by the widespread presence of degradation phenomena-such as cracking, flaking, and delamination-affecting all black surfaces. The research aims to elucidate the correlation between Saura's material choices and the observed deterioration. A combination of multiband imaging and portable digital microscopy is employed to document the morphology and distribution of crack patterns. Additionally, elemental analysis such as XRF and microinvasive analytical techniques, including mu -Raman spectroscopy, ATR-FTIR, and GC-MS, was used to characterize pigments, binding media, paint additives, and degradation products. Findings reveal that Saura primarily employs commercial oil-based paints with opaque, glossy finishes. Variations in crack morphology are linked to the intrinsic properties of specific pigments-such as zinc white, titanium white, cerussite, hydrocerussite, bone black, and iron oxides-and their interactions with binding media (drying oils and alkyd resins), as well as environmental conditions. This research provides new insights into Saura's materials and highlights key issues, while proposing a methodological framework applicable to studying degradation phenomena in modern and contemporary artworks.