Il gel di Opuntia: una proposta sostenibile per il consolidamento di pitture murali "a secco"

A new light on the use of natural materials in the restoration sector arises from the need and duty to study sustainable alternatives on an environmental, economic and cultural level. Prickly pear gel is a vegetal mucilage, extracted from the blades of the plant. In Italy the prickly pear is grown exclusively for the sale of its fruit, while the blades represent the waste from annual pruning, for an amount of almost 10 t/h. In Mexico, the prickly pear gel’s properties have been exploited since the pre-Columbian era to modify and improve the characteristics of some materials used in construction and coatings. Studies over the last 30 years demonstrate promising results in the conservative field for a multitude of applications. In this study, the use of gel for the conservation of "dry" wall paintings is reported. The experimental study involved the preparation of mockups, carried out to reproduce the "dry" execution techniques found in historic buildings in Italy: lime, egg and glue tempera and the so-called "tempera grassa" (egg-oil). Mucilage’s performances were evaluated by spectrophotometry, contact angle, peeling test, and ultrasound investigations performed before and after the consolidation phase. The results show how the mucilage improved the internal and surface cohesion of the mockups in all the execution techniques, without causing surface variations in colorimetry, wettability and decreasing the bioreceptivity of the layers.