Early Iron Age gold buttons from South-Western Iberian Peninsula. Identification of a gold metallurgical workshop

Abstract

Early Iron Age gold buttons from Castro dos Ratinhos, Fortios and Outeiro da Cabeça were analysed by conventional EDXRF, Micro-PIXE, SEM-EDS and Optical Microscopy. EDXRF results point out to a rather homogeneous alloy composition throughout all the analysed buttons. PIXE microanalyses show that all the button components (disk, tab and peripheral grooved decorated rod) have the same alloy composition. PIXE and SEM-EDS microanalyses, supplemented with optical microscopy characterization, show the absence of chemical composition differences between distinct components and joining zones, suggesting that no solder had been applied, i.e. that a partial melting/solid state diffusion process had been used for the welding of button components. Finally, the noticeable similar compositions together with the use of the same welding process and the very similar artefact typologies suggest that those small gold treasures could be interpreted as the result of the work of a single metallurgical workshop, probably located somewhere in the South-Western Iberian Peninsula. RESUMEN

Bronze Age and Iron Age gold torcs and earrings from the Iberian Atlantic façade: a non‐invasive multi‐analytical approach to the characterisation of the alloys and the corrosion

“…Due to the diameter of the X‐ray beam, the analyses of the composite objects were carried out on their main parts only: the rods in the case of the torcs and the body rings in the case of the earrings. The data published for the IA torc from Chaves together with previous data from OES for several torcs and earrings have been added to Table . Tables and list the data obtained by μ PIXE for the three C beads and three IA earrings made from granules and wires soldered to a main solid rounded body ring.…”

Una revisión de los discos de Fortios

“…EDXRF analyses of the gold buttons from each site present analogous gold, silver and copper contents indicating that the different components of each button are very probably made from the same gold alloy. Besides the elemental composition of these jewels is similar whatever their origin, Fortios, Outeiro da Cabeça or Castro dos Ratinhos (Soares et al 2010: Micro-PIXE analyses of the gold buttons from Castro dos Ratinhos involved the quantification of several points from different components (disk, tab, and rod) of each button. Results show similar compositions regardless of which component was analyzed.…”

“…Our results, both for EDXRF and Micro-PIXE, were obtained considering the measured Au-L and Ag-K lines intensity. As we noted in our previous paper (Soares et al 2010) our SEM-EDS analysis were performed with a Zeiss DSM 962 with an Oxford Instruments INCAx-sight EDS spectrometer, and the mounted cross section of the gold button sample was highly polished before analysis. Although not listed in our previous paper, the experimental conditions used for SEM-EDS data acquisition were: accelerating voltage 20 kV, working distance 25 mm, EDS take-off angle 30 degrees, emission current adjusted to 70 µA, dead time adjusted to 30%, live time 120 s (process time 3); standardless quantitative analysis (semi-quantification by ZAF correction), with a EDS resolution of 133 eV at 5.9 keV; energy calibration with a cobalt sample.…”

“…The only analytical technique these authors used to determine the elemental composition and to identify the technique used to join the components of the so-called gold disks was SEM-EDS. In our work (Soares et al 2010), we analyzed not only 5 gold disks (or gold buttons, as we called them) from Fortios, but also 23 from Outeiro da Cabeça and 7 from Castro dos Ratinhos, using several analytical techniques, namely EDXRF, Micro-PIXE, Optical Microscopy (metallographic analysis) and also SEM-EDS.…”

“…These have a very similar typology and were found at three archaeological sites in the South-Western part of the Iberian Peninsula. A set of 35 buttons from Castro dos Ratinhos (7), Outeiro da Cabeça (23) and Fortios (5) were analyzed and the results published in Trabajos de Prehistoria (Soares et al 2010). Recently Perea et al (2016) have published analyses of other 4 gold buttons from Fortios with the same purpose, but only using one technique, SEM-EDS.…”