Compositional and microstructural study of joining methods in archaeological gold objects

Abstract

This work arises in response to the need to understand the production techniques of pre‐roman gold jewels, starting from the systematic characterization of the different methods of metal joining used in antiquity to produce these objects. To meet this requirement, different procedures used in antiquity were reproduced by means of experimental archaeology. These models correspond to three metal‐joining methods reported by ancient recipes: solid‐state diffusion with copper salt, brazing and autogenous welding. These techniques were studied by different analytical methods in order to characterize them at both compositional and microstructural level (SEM‐EDS, metallography, μ‐XRF and μ‐PIXE). The results obtained show that the solid‐state diffusion bonding with copper salt presents a crystal hexagonal structure without phase changes in the joining point, where only a variation in the grain size is observed. At the compositional level, this soldering method is characterized by a local increase in copper concentration and a small decrease in gold content. In contrast, brazing shows a dendritic‐porous structure due to the superposition of the soldering alloy and the crystal structure of the original foils. Besides, the compositional analysis revealed an increment of silver and copper concentrations and a simultaneous reduction of gold concentration. Finally, in the autogenous welding, no changes at the microstructural and compositional levels were observed. The results obtained have also demonstrated the usefulness of a portable μ‐XRF system for the in‐situ characterization of ancient jewels. Copyright © 2017 John Wiley & Sons, Ltd.

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