New Insights into the Materials and Painting Techniques of Ancient Wall Paintings from the Roman Province of Dacia: A Minimally Invasive Multi-Method Approach

A group of wall painting fragments discovered at Ulpia Traiana Sarmizegetusa, an important Roman archeological site located in the former Roman province of Dacia (Romania), have been investigated with the aim of defining the material composition of their pictorial layers and exploring the pictorial technology used. In order to preserve the integrity of the murals and minimize sampling, an array of non- and micro-invasive techniques has been employed, including X-ray fluorescence, laser-induced breakdown spectroscopy, Fourier transform infrared spectroscopy, and hyperspectral imaging. In accordance with previous studies, the identified color palette was mainly based on iron-rich earth pigments (red and yellow ochres, green earth) and carbon-based blacks (soot/charcoal, bone black). Egyptian blue, lazurite, some lead-based pigments, and potentially indigo were also identified (in complex mixtures) on the uppermost paint layers, typically applied a secco over the a fresco background. The presence of expensive pigments and the existence of a red preparatory drawing, documented for the first time in the region, indicate that the original wall paintings had elaborate schemes and, secondly, reflect the patron’s wealth and social status. Hyperspectral imaging was able to retrieve some faded paint layers in certain cases, helping to recover lost decorative details, an indicator of a more complex polychromy compared to what we see today. The obtained results add important contributions to the limited corpus of data regarding the technical know-how of decorative polychrome painting on plaster found in Roman archeological sites in Romania.