Mechanical Characterization of Gesso and Pigments for Egg Tempera Painting

This study investigates the mechanical properties of traditional painting materials used in egg tempera techniques: gesso grounds and pigmented egg tempera layers. Gesso samples were prepared using rabbit skin glue, calcium carbonate, and titanium white pigment, while egg tempera samples were formulated with four different pigments (Titanio Rutilio, Bianco Zinco Sigillo Oro, Ocra Gialla, and Blu Ercolano) in egg yolk binder. Mechanical characterization was performed using micro-tensile and peeling tests. The results indicate that the mechanical properties of gesso are significantly influenced by the Pigment Mass Concentration (PMC), where higher PMC values result in reduced elastic modulus and ultimate tensile strength. Among egg tempera formulations, elastic modulus varied dramatically (29.6-970.7 MPa), with Ocra Gialla demonstrating the highest stiffness and Titanio exhibiting exceptional deformability (4% strain at failure). The adhesive fracture energy of these materials was also evaluated, providing insights into their fracture behavior and adhesion strength. These findings contribute to the understanding of historical painting materials' mechanical performance, aiding in conservation and restoration efforts by optimizing preservation strategies based on material behavior.