Composition and manufacture of a rare gold example of the Mesopotamian “tree of life” iconography and coeval jewellery in southwestern Iberian Peninsula

The study of gold jewellery can provide important answers about the diffusion of goldsmith technologies and cultural beliefs in Mediterranean World. This work comprises gold ornaments recovered from archaeological contexts dated to the 1st millennium BC in southern Portugal, with special emphasis to two exceptional plaques portraying the Mesopotamian iconography of the “tree of life”, in addition to two rings, the so-called nezems, whose prototype also derived from Orientalising contexts. The set of gold items is completed with a fragment of an ornament such as a pendant or earring. The jewellery was characterised by p-EDXRF, SEM–EDS and optical microscopy to identify the production techniques and composition, while the reflectance transformation imaging technique was used to enhance the study of iconographic motifs. Some manufacturing processes were identified, namely the decoration with stamping on the “tree of life” plaques, a technique similar to strip-drawing on the nezems and the brazing with Au–Ag–(Cu) solder on the small fragment. Overall, the set showed gold alloys with highly variable silver contents (11–39 wt%), but rather constant copper amounts (1.8–2.5 wt%). The composition of individual items helped to establish associations, such as the use of an identical alloy for the pair of plaques. Moreover, the two nezems were made with gold of different purity probably due to economic reasons. Finally, the gold alloy compositions were compared with others from different collections in Iberian Peninsula and Eastern Mediterranean region, providing clues about the gold alloys used by ancient goldsmith workshops.