Tung Oil and Linseed Oil as Traditional Finishing Materials Important for Furniture Conservation

Tung oil and linseed oil are two representative traditional drying oils wich were commonly employed, for centuries, for wood finishing. Therefore, their study in terms of properties, chemical structure features and alterations by ageing is important for furniture conservation. This paper focusses on some comparative properties of Tung oil and linseed oil as wood finishing materials. For this purpose, test wooden samples of Chinese walnut (Juglans mandshurica Maxim.) were coated with these materials by manual traditional techniques. Solids content of the oils was determined in order to approximate the thickness of the resulting film. The colour change brought about by coating of wood surfaces with these oils was measured in the CIELab system. Furthermore, an accelerated artificial ageing test under the action of temperature (100°C) was performed in order to evaluate and compare the ageing resistance of the two types of oils. Ageing phenomena were investigated by colour measurements and FTIR ATR spectrometry. Both uncoated and oils coated wood surfaces suffered colour changes observed as darkening and colour shade shifting to red and yellow, but these were obviously more evident for the oil coated samples. The overal colour changes were maximum for the samples finished with linseed oil, while tung oil semmed to be more resistant. FTIR investigations for two types of oils highlighted similarities and differences in their chemical composition, curing and aspects of the thermally induced ageing mechanism. The later proved to be mainly an oxidative degradation process leading to formation of free fatty acids and other carbonyl containing compounds, as suggested by the broader carbonyl (1740 cm) and hydroxyl bands (3400 cm).