An exceptionally perennial surface artwork: fresco on lime or on cement
Résumé
The paper describes the near-surface microstructure of artistic frescoes and compares the traditional fresco technique in which the pigments are applied on a fresh lime intonaco with the more recent technique in which the lime intonaco is replaced by a fresh cement plaster. The study is performed on artworks produced at different periods: one Roman fresco fragment dated from the first century CE, samples from a Renaissance Botticelli fresco and two works by a 20th century artist, Henri Marret, one on a lime intonaco and the other on a cement plaster. A special attention is given to the nature of the pigments used, to their position and adhesion process near the surface and to the colorimetric analysis of the pieces. The characterization of the different objects (performed by optical microscopy, scanning electron microscopy and microanalysis, colorimetric measurements and X-ray diffraction) gives full information on the influence of the artist's technique on the adhesion process and durability of the coloured decoration. It is proved that fresco painting on fresh cement, although considered at the beginning as not as efficient as fresco on lime, leads to a similar mechanism of pigment adhesion and probably to a similar durability.