Thermogravimetric study on the ageing of lime wood supports of old paintings

This paper presents thermogravimetric data of some samples of soft lime tree (Tillia cordata Mill) wood from the structure of the supports of old paintings (mobile icons and iconostasis) 100-200 years old. In order to determine the ageing processes, the physical, structural and chemical changes that have occurred in time under the influence of environment have been correlated with thermogravimetric data. It has been established that the thermal characteristics for the elimination of physically adsorbed water depend on the sample's age and on the conservation treatments. The variation of the thermal characteristics with the wood age is important for the main decomposition step. The temperatures for the onset and the maximum rate of degradation as well as the global activation energy increase with the wood's age while the weight loss decreases. These characteristics could be used to assess the age and conservation status of the paintings. The variation of the characteristics could be due both to the loss in time of the volatile compounds that lead to lower thermal characteristics and to the structural changes occurring in the wood that, for the highly deteriorated and/or degraded wood leads to a totally different thermal behaviour. (C) 2003 Elsevier Science Ltd. All rights reserved.