Mucilage and Gum of Opuntia spp. as Sustainable Binders for Pictorial Retouching

The mucilage of Opuntia ficus-indica and the gum of Opuntia cochinera—a pathological exudate—are natural biopolymers historically documented in pre-Hispanic artistic and construction techniques. This study explores their potential as binders for the formulation of retouching materials in cultural heritage conservation. Both biopolymers were characterized using FTIR and DART-MS, and pigment–binder systems were formulated and applied to traditional substrates. Strati-graphic cross-sections were analyzed by SEM-EDS to assess the morphology of the paint layers and their interaction with the grounds. Comparative analyses with gum arabic (the reference binder for this type of application) revealed similar structural features, while FORS investigations highlighted distinctive optical responses. These findings suggest that Opuntia-based binders can provide novel optical properties and broaden the range of sustainable solutions available for pictorial retouching. Overall, the results support the potential use of O. ficus-indica mucilage and O. cochinera gum as innovative natural binders in conservation practice.