DIAGNOSTIC AND EXPERIMENTAL APPROACHES FOR THE CONSERVATION OF GYPSUM REPLICAS: FROM INDOOR CLIMATE ASSESSMENT TO AGEING-INDUCED MATERIAL TRANSFORMATION

In this PhD thesis, a diagnostic and experimental study was conducted to investigate the conservation behaviour of gypsum-based replicas used in 19th century heritage collections. These casts, widely adopted for educational and display purposes in museums, are often housed in indoor environments lacking environmental control, making them highly vulnerable to degradation. The first part of the study focuses on selected group of historical plaster replicas conserved at the Museum of Roman Civilisation, in Rome, combining microclimatic monitoring with non-invasive and micro-invasive analyses to assess their composition, state of conservation, and the relationship with the indoor microclimatic conditions to which they are exposed. In the second phase, mock-up samples replicating historical formulations were prepared and subjected to artificial ageing to evaluate the material response and the effectiveness of protective treatments commonly applied in conservation practice, using a combination of analytical techniques including Fourier-Transform Infrared spectroscopy, optical profilometry, scanning electron microscopy, and colourimetric analysis. The final part of the research investigates the pore structures and their relationship with environmental factors, using a multi-analytical and multi-scale approach. Techniques such as nitrogen physisorption, mercury intrusion porosimetry, imaging digital analysis and X-ray micro-tomography were employed to characterise porosity before and after artificial ageing. By combining the study of historical case studies with controlled laboratory experiments, this research provides new insight into the deterioration mechanisms of gypsum materials and supports the development of preventive conservation strategies that account for their physical properties and response to indoor environmental stresses.