In Situ Conservation of the Roman Mosaics at the Villa of Boscéaz (Orbe, Switzerland): Diagnosis of Risks Involved

In order to maintain the archaeological integrity of the site of Bosceaz, one of the most remarkable north of the Alps because of the number and quality of its roman mosaics, it is intended to maintain these in situ and on their original support. This mode of conservation implies many risks, mainly linked to the climatic variations and to the presence of water and salts in the ground and the mosaics. The high degree of damage observed on these mosaics discovered more than 150 years ago illustrates this fact. The aim of this study has been to establish a diagnosis of the risks linked to the uncovering and the in situ conservation of a mosaic recently discovered (currently covered with protective materials). This diagnosis has been established on the basis of the measurement of the physical and chemical properties of the mosaic and the ground. It turned out that the rising of salts from the ground to the mosaic would be the major problem and that consequently a dessalaision will have to be carried out. Concerning the choice of the climatic conditions for conservation, the critical zone in which the salts present crystallize was determined. The thermal dilatation of the materials appeared relatively small, but might become damageable in the long term because of a possible hysteresis. The hydrie dilatation turned out to be negligible.