Towards standardisation of moisture content measurements in cultural heritage materials

Standards developed for industrial or commercial purposes cannot be applied to cultural heritage for two reasons: some methodologies are invasive/destructive; others are not destructive but have readings in arbitrary units and calibration is hardly possible for the specific case of cultural heritage materials that are weathered, chemically degraded, transformed, or affected by fungi or insects. This paper discusses the definition of moisture content for cultural heritage materials and its dependence on the measuring methodology, absolute and relative readings typical of various methodologies, the uncertainties of the most popular methodologies used by conservators and restorers, such as oven-dry weighing, calcium carbide pressure, conductive, capacitive, microwaves, equilibrium relative humidity, andthe problem of calibration for cultural heritage materials.