Archaeometallurgical analysis of the bow drill from the fifth century BC Ma‘agan Mikhael shipwreck

Three bow drills were discovered in the 400 BC Ma‘agan Mikhael ship. Radiography revealed a square cross-section recess for the bit in the wooden stock of one of the drills. Metal particles, remains of a bit, survived in the recess. The metal composition, microstructure and manufacturing technology of the bit were studied using non-destructive and minimally destructive testing methods. These comprised digital radiography, light microscopy, X-ray fluorescence analysis, scanning electronic microscopy–energy-dispersive X-ray spectroscopy analysis, and micro-hardness indentation tests. The results demonstrated that the bit was made of wrought iron manufactured by the direct smelting process. A martensitic microstructure was observed after etching the external part of the bit. Examination of the iron oxide areas revealed a layered microstructure. Therefore, it is suggested that the bit was probably manufactured by forge-welding thin alternating layers of carburized wrought iron, which was heat-treated and quenched without tempering. This microstructure improved the hardness and strength of the metal. This is the first time that a metal bit found on a shipwreck of the period has been metallurgically investigated. It shows that the ancient blacksmiths produced the drill bit using the most suitable materials and advanced manufacturing processes. This information enlarges our limited knowledge about the use of carpenter’s tools in the East Greek/Phocaean fifth century BC shipbuilding tradition.