SUPERCRITICAL DRYING PROCESS IN CONSERVATION OF WATERLOGGED OSTEOLOGICAL REMAINS

摘要

This poster shows a supercritical drying process in conservation of waterlogged osteological remains. The specimens were collected during the 1997-2000 excavation campaigns in a Neolithic village, now submerged, located in the South-Eastern area of the Bracciano Lake in a locality called "La Marmotta" (Anguillara Sabazia, Rome, Italy). The escavation started in 1989 and it is still continuing by the Soprintendenza Speciale al Museo Nazionale Preistorico ed Etnografico "Luigi Pigorini". A first set of experiments were performed on bench-scale equipment (DIONEX 703, 32 ml volume cell) to verify the technical feasibility of the process. Then, the process was performed on bigger scale (800 and 3000 ml volume extractors). The process is divided into two steps. First, a supercritical mixture of CO_2 and methanol flows through the specimens and slowly removes the water, substituting it. Then, treatment with pure supercritical CO_2 removes the methanol residues. During the process, viscosimetric measures were performed to control the water content of the . methanol "extract" collected in the separation unit: evaluating the amount of extracted water, it was possible to stop the process when the specimen was allegedly dry. The process was applied to different kind of osteological remains ("hard" and "soft") with good results in terms of water recover and drying of the archaeological artefacts.