Non-Destructive Investigation of Pre-Columbian Goldwork from Panama with Variable Pressure Scanning Electron Microscopy

Abstract

-Columbian gold alloy objects from Panama were examined and analyzed using optical microscopy and a variety of non-destructive instrumental techniques including x-ray fluorescence analysis (XRF) and variable pressure scanning electron microscopy with energy dispersive spectroscopy (VP-SEM-EDS). The 309 objects in the collections of the National Museum of the American Indian (NMAI) and National Museum of Natural History (NMNH), as well as nine objects brought back from recent excavations in Panama, underwent to investigate the technology of goldworking in ancient Panama.Goldworking technology spread to Panama from neighboring regions in the first centuries AD; however, not all metalworking techniques were adopted and many stylistic and technological variations developed locally [1]. Almost all of the objects examined in this study were fabricated from Au-Ag-Cu alloys and include: pendants, plaques, nose rings, finger rings, ear rods, bands, cuffs, sheathing, beads, and tools.Optical microscopy alone was capable of providing a great deal of technological information such as primary fabrication method (e.g. cast vs. hammered), as well as some joining and finishing techniques. Examination of every object in the study was therefore carried out under the stereomicroscope while evidence of manufacture was recorded with photomicrographs and entered into the project database.In cases where the methods of fabrication and joining remained unclear from examination under the microscope, objects were selected to undergo VP-SEM-EDS. As only non-destructive analysis was permitted on the Smithsonian material, this technique was ideal to help answer research questions not resolved with optical microscopy or XRF. Whole objects were placed in the sample chamber without any additional sample preparation and were analyzed at full-vacuum or in variable pressure mode depending on the object and presence of polymer coatings from conservation treatments. Imaging of objects was performed with a Hitachi S-3700N VP-SEM and elemental mapping was carried out with a Bruker EDS. All objects were analyzed at 15 keV at 10-15 mm working distance.Despite the limitations of non-destructive and purely qualitative analysis, the high magnification imaging and elemental mapping provided by VP-SEM-EDS were effective in characterizing individual objects. This in turn allowed documentation of the wide range of goldworking technologies used in ancient Panama. For example, dendritic structures from casting were clearly visible in SEM images and coring was distinguishable through elemental mapping ( fig.1).