Integrated analytical techniques for the study of composite waterproof caulking materials used on the Nanhai Ⅰ ancient shipwreck of the Southern Song Dynasty

Abstract

“Nianliao” is an organic-inorganic composite material historically employed in ancient Chinese wooden ship construction for gap filling and waterproofing. This study examines two types of Nianliao samples from the Nanhai I shipwreck of the Southern Song Dynasty (1127–1279 CE): fiber-containing Nianliao and pure putty Nianliao. The objective of this research is to develop a systematic analytical method for this ancient composite material, thereby uncovering the production techniques and characteristics of historical Chinese waterproofing caulking materials. To analyze the organic components of Nianliao, we introduced a novel and rapid method utilizing ultra-high-performance supercritical fluid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPSFC-QTOF/MS). This approach facilitates the direct analysis of fatty acids in Nianliao samples without derivatization, successfully isolating and identifying various free fatty acids and their oxidation products. Based on these findings, we infer that tung oil constitutes the organic component of the Nianliao samples. Additionally, the study elucidates the composition, aging characteristics, and interactions of Nianliao components through complementary instrumental analytical techniques. Inorganic compounds were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). These analyses revealed that the primary inorganic component was calcium carbonate, formed through lime carbonation. Calcium salts of fatty acids were also detected, indicating a reaction between tung oil and lime that facilitated the integration of organic and inorganic components. Fibers present in some samples were analyzed based on their longitudinal and transverse morphological characteristics and identified as hemp fibers. Furthermore, differential scanning calorimetry-thermogravimetry (DSC-TG) was employed for quantitative analysis. This analysis revealed significant differences in organic content between the two types of Nianliao samples, which influenced their microstructural properties. Specifically, the fiber-containing Nianliao samples exhibited a denser microstructure and contained approximately four times more tung oil compared to the pure putty Nianliao samples. This research provides novel insights and methodologies for analyzing organic compounds in archaeological contexts. It establishes a scientific foundation for the restoration and archaeological study of ancient wooden shipwrecks and contributes to the development of effective conservation strategies.