Archaeometallurgical Investigation of Joining Processes of Metal Objects from Shipwrecks: Three Test Cases

Abstract

This article presents archaeometallurgical research of three types of metal objects excavated underwater from two shipwrecks in Israel: Tantura F (mid-seventh-end of eighth centuries ad) and Akko 1 (first third of nineteenth century). Both non-destructive and destructive methods were employed. The finds were manufactured by joining processes; therefore, the studies concentrated on metallurgical processes. However, these researches were multidisciplinary, combining typological analyses of the archeological objects, as well as the historical perspective. The first case study is of an iron anchor from the Tantura F shipwreck. This anchor has a typical heterogeneous wrought iron microstructure of ferrite–pearlite–cementite and Widmanstatten plates, manufactured from several blooms made by the direct process. The blooms were joined using forge-welding by an expert blacksmith, resulting in a high-quality iron product. The blooms used in the anchor’s circular cross-section shank were forge-welded from iron and steel pieces, producing a composite material with superior mechanical properties. The second case study presents a 12-pdr cannonball from the Akko 1 shipwreck. The cannonball was manufactured from high-quality wrought iron, with a homogenous microstructure of iron matrix and rather large equiaxed α-ferrite grains, produced by an indirect technique, using the hot-forge-welding process. As its production technique pre-dates that of the ship, it is suggested that this cannonball was manufactured in a different place and by a different technology from the other cannonballs found in the shipwreck. It is also possible that the 12-pdr cannonball might have been used as ballast. The third case study deals with brass cases from the Akko 1 shipwreck. The cases were made of brass containing equiaxed α-brass grains with twins, manufactured from rolled sheets that may have originated in Great Britain. The parts were joined by soldering with tin–lead alloy, and it is suggested that the cases were made in an Egyptian workshop.