This article investigates the colour change in bluish-grey limestones, focusing on the fading observed in Azul Valverde and Atlantic Blue varieties when exposed to weathering conditions. The study utilised various techniques, including synchrotron radiation at the European Synchrotron Radiation Facility, to analyse iron speciation in these ornamental stones. The presence of Fe2+ and Fe3+ was linked to greyish and yellow/brown colours, respectively, while UV radiation from the sun accelerated bleaching of dark blue/grey polished limestone.
The research delved into the chemical and mineralogical characterization of polished limestone exposed to outdoor atmospheric conditions, revealing the impact of UV radiation on stone ageing and fading. XANES spectra analysis provided insights into the electronic state of iron in limestone, highlighting the sensitivity of the pre-edge region to electronic structure variations. SEM and DTA-TG analyses showed changes in morphology and elemental composition, while XRD patterns compared the properties of different limestone samples before and after exposure.
The geological setting and features of bluish-grey limestone were explored, emphasising the fault systems and tectonics of the Maciço Calcário Estremenho and the limestone’s age ranging from the Lower Jurassic to Cretaceous. The study contributes to a better understanding of the mechanisms behind colour changes in limestones, shedding light on the interplay between UV radiation, iron speciation, and the resulting colour variations.
Overall, the research provides valuable insights into the factors influencing the colour stability of bluish-grey limestones and the implications for their preservation in outdoor environments.
