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 Widmanstätten 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 a-ferrite grains, produced by an indirect technique, using the hot-forgewelding 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 a-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.

The Tantura F shipwreck: hull remains and finds-final report

“…Two iron anchors were found in the shipwreck site (Figs A and B). The anchors have been studied extensively by typological and archaeometallurgical methods (Eliyahu et al ., ; Aronson et al ., ; Ashkenazi et al ., ). Anchor A was found on the port side, beneath and touching the hull.…”

Another Link in the Chain: Archaeometallurgical Investigation of an Anchor Chain from the Nineteenth Century Akko Tower Shipwreck

“…174-175]. A satisfactory forge-welding process provided appropriate mechanical deformation (thickness reduction) to create the contact between the parts to be joined, and flux material to help clean the surfaces to be joined [11,21]. As the deformation during the forge-welding process increases, the bond strength will increase until it reaches an optimal deformation value, which depends on both material and process parameters [22, p. 227].…”

“…When two wrought iron parts are forge welded, some residual oxides are entrapped along the weld [26,27]. Nevertheless, several thermo-mechanical operations of heating and forging may result in homogenizing the wrought iron matrix and correspondingly deleting the welding line [17,21].…”

X-rays investigations for the characterization of two 17th century brass instruments from Nuremberg

“…Generally, Yellow Brass and in particular the α-brass (with up to about 32.5 wt. % zinc) are ductile, easily cold-worked, can be rolled or hammered into thin sheets, and have good corrosion resistance in a salt-water atmosphere [26], and for these reasons, it was extensively employed for the making of historical brasses [10], [27]. The presence of several trace elements was the proof of the traditional cementation method employed by the early craftsmen to obtain brass, which included the use of calamine (a high-grade zinc carbonate ore).…”

“…The other solder joints are soft solder assembled with Pb-Sn solder containing a variable ratio of the elements (Table 2). The use of this kind of solder is largely documented in ancient copper-based objects and the proportions of the elements can vary from 30% Pb (and 70% Sn), to as much as 98% Pb (and only 2% Sn) [26], [39]- [42]. The results about the soldering and the similarity between the alloys of the mouthpipes joint in both Table 1.…”