Analysis and identification of tung oil in the caulking materials from the “Nanhai Ⅰ” shipwreck of the Southern Song Dynasty

As a key waterproofing material used in the construction of ancient wooden ships, the organic components of the jointing material (caulking material) are crucial for maintaining the water tightness of the hull. In order to identify the organic components of the caulking material used in the “NanhaiI” shipwreck, dating from the Southern Song Dynasty, a comparative analysis was conducted between raw tung oil and modern tung oil-based caulking material using mass spectrometry. The results indicate that the specific free fatty acids and oxidation products of unsaturated fatty acids in tung oil can serve as markers for the identification of tung oil in caulking materials. Further, the caulking material samples from the “NanhaiI” shipwreck were analyzed by ultra-performance liquid chromatography-mass spectrometry (UPLC-QTOF/MS). Five specific fatty acids, namely α-tung acid, linoleic acid, oleic acid, palmitic acid and stearic acid, as well as the oxidation products of unsaturated fatty acids (α-tung acid, linoleic acid and oleic acid) were successfully identified. The results show that the organic component of the caulking material used in the “NanhaiI” shipwreck is tung oil. This discovery not only provides an important reference for the study of ancient shipbuilding techniques but also offers a scientific basis for the protection and restoration of sunken ships.