Microscopic techniques and a multi-analytical approach to study the fire damage of the painted stuccoes from the Petruzzelli Theatre (Bari, Southern Italy)

This paper reports a study of the effects of fire on the decorative stucco elements consisting of painted mouldings and decorations in the Petruzzelli Theatre in Bari (Southern Italy). The theatre was built at the end of the nineteenth century. In 1991 a fire caused serious damage to both materials and structure.Visible damage to the decorations included various deterioration patterns. The fire-related effects on both plaster and painted surface layers were subjected to in-depth investigation under laboratory conditions by focusing on mineralogical, chemical and microstructural alterations. Methods used included Optical Microscopy, Environmental Scanning Electron Microscopy coupled with X-ray microanalysis, X-ray Diffraction, Fourier transform infrared spectroscopy and simultaneous Thermogravimetry-Differential Scanning Calorimetry.De-hydration of the gypsum binder and oxidation of the iron compounds caused new mineralogical phases to form in the stucco plaster. In some cases, microscopic observation suggested that calcination of the lime binder may have occurred in thin layers under the surface. Significant microstructural modifications were detected in the form of cracks and microcracks, due to thermal shock and gypsum dehydration. Phase transformations affected the structural integrity and the colour properties of the stucco plaster to different extents, up to a maximum depth of around 2.5. cm, while fissuring due to thermal shock penetrated to greater depths.Fire-related damage in the surface paint consisted of colour changes and/or disruption of the painted layers due to thermally-induced chemical reactions involving mineral pigments; detachment and burning of the painted layers from the direct action of flames, as well as accumulation of combustion deposits on the surface were also observed.