Freeze-drying and cultural heritage: An overview

This paper aims to provide an overview of the application of freeze-drying in the field of cultural heritage. The possibility of removing water from an object at low temperature, thus preserving most of its specific features that would be lost at high temperature, makes the process the elective choice when restoring water damaged materials. Flooded archives and libraries, due to natural events or to the intervention of fire extinguishing systems, are a typical case where freeze-drying can be applied since the material, after flooding, is brought to a low temperature as soon as possible to cause the water to freeze and, therefore, to block the degradation of the material. Besides, freeze-drying may be used to preserve archaeological finds, e.g. waterlogged woods or wet textiles, by means of water removal. Anyway, in all these cases specific issues must be faced, aiming to preserve the mechanical properties of the object, and this may require ad hoc pretreatments. It must be highlighted that in some cases the occurrence of a freeze-drying process, in particular of the atmospheric freeze-drying process, is undesired for the preservation of finds, and this must be carefully managed. Finally, the possibility of using freeze-drying to create works of art will also be addressed.