The Sacri Monti (Holy Mounts) in Lombardy and Piedmont (Ossuccio, Varese, Orta, and Varallo) show with a series of chapels a sacred tale (life of Christ, life of the saints). In each chapel there are many terracotta statues with a painted background. Mineralogical, chemical, and physical analyses were carried out. The terracottas are differentiated by the temperature of firing (500°C, Orta; 700°C, Ossuccio). The greatest decay, caused by frost, is found at Orta where the terracottas have a lower heating temperature and where the air humidity is greater.