Characterizing the sealing materials of the merchant ship Nanhai I of the Southern Song Dynasty

Nanhai I is a highly valuable shipwreck of the Southern Song Dynasty for studying various topics, including the shipbuilding techniques. The sealing materials are of significant importance to ensure the ship's reliability during the voyage across the ocean and they were rarely analyzed. Therefore, the sealing materials of this ship were analyzed by several analytical approaches. The sealing materials included two types, i.e., gap filler with jute fibers and surface coating without any oakum. The main components of both types of putty are calcite with minor Tung oil. The weight ratio of Ca(OH)(2)/Tung oil range from 4.3:1 to 7.9:1 for surface coating samples and the weight ratio of Ca(OH)(2)/organics is 3.1:1 for the gap filler sample. Additionally, we first find that the surface coating has a layered structure, where outer layers contain more Tung oil than inner layers. The innermost layer of the surface coating sample might be altered by organic acids from wood deterioration, causing its loose structure and grey color. The composite layers with different formula might be a result of balancing the costs and performances of the putty.

Automated summary

The sealing materials of the Nanhai I shipwreck, including gap filler with jute fibers and surface coating without oakum, were analyzed to reveal a layered structure in the surface coating with varying compositions of Tung oil. The innermost layer of the surface coating may have been altered by organic acids from wood deterioration, resulting in a loose structure and grey color. The different formula of composite layers in the sealing materials suggests a balance between cost and performance.