Hygroscopicity and Vibrational Properties of Aged and Heat-treated Wood

It is believed that acoustic quality and stability of wood are improved during long term ageing. However, it has recently been suggested that a part of those ageing effects are recovered by moistening at high humidity. Similar temporary effects have been recognized when wood is heated at high temperatures in the presence of moisture. Those temporary changes are speculated to be due to the physical ageing of amorphous wood polymers involving the temporary closure of micropores in the wood cell wall. For appropriate conservation of old wooden musical instruments and cultural properties, the recovery of physical properties due to moistening in humid condition should be taken into consideration. In addition, the temporary effect of heating should be eliminated for precise evaluation of the practical performances of heat-treated wood. This paper describes the reversible and irreversible changes in wood properties relevant to the practical quality of wooden crafts and musical instruments due to natural ageing and heat treatment.