Experimental investigation of tensile and adhesive properties in gesso and egg tempera systems

This study presents a systematic mechanical characterization of traditional materials employed in egg tempera painting techniques, focusing on gesso grounds and pigmented egg tempera layers. Gesso samples were prepared using rabbit skin glue, calcium carbonate, and titanium white pigment, while tempera paints were formulated with egg yolk binder and four representative mineral pigments: titanium white (TW), zinc white (ZW), yellow ochre (YO), and ultramarine blue (UB). Mechanical performance was assessed through micro-tensile and peeling tests. For gesso, the results demonstrate a strong dependence on Pigment Volume Concentration (PVC), with higher PVC values leading to reductions in both elastic modulus and ultimate tensile strength. For tempera paints, marked variability in elastic modulus was observed, with yellow ochre exhibiting the highest stiffness, whereas Titanium-rich formulations showed the greatest strain capacity at failure. In addition, adhesive fracture energy was quantified, providing the first dataset on the peeling resistance of these traditional materials. The results offer new insights into the fracture and adhesion behavior of tempera systems and establish a robust experimental framework that can support the development of conservation strategies for historical paintings.