A multidisciplinary approach to investigate the peculiar artistic technique of Scagliola: Modern age decorations in Hadrian's Villa (Tivoli, Italy)

In the present work, a multi-technique approach was adopted to study and characterize six polychrome deco-rated elements found in the storerooms of the archaeological site of Hadrian's Villa in Tivoli (Rome). In particular, preliminary microscope observations along with mu-Raman and FT-IR spectroscopies and FESEM-EDS analyses were adopted to identify the used materials and the execution technique. This information could allow placing the artefacts in a chronological context, in particular by evaluating possible coherences with the modern phases of the archaeological site. At first visual observation, both stylistic and technical details suggested that the artefacts had been performed by using Scagliola, a particular and not deeply investigated artistic technique developed in Europe at the end of the XVI century for interior decorations. The acquired information has been compared with data obtained by similar in-situ decorations, found on the vault of the Casino Fede, an XVIII century building of the Villa. The characterization of the constituent materials revealed a rich palette, based on both inorganic and organic pigments, some alteration products, and a massive presence of gypsum in the matrix. These results led to confirm the use of Scagliola technique in the realization of all the artefacts, even though this information is not sufficient to confirm if they belong to the same building. Furthermore, a peculiar result was the identification of arsenic-based pigments as pararealgar and amorphous arsenic sulphide as an orange pigment. In particular, pararealgar was identified as the initial material used for the synthesis of the amorphous pigment, a very rare identification in artworks.