Microscopic Identification of Micro-Organisms on Pre-Viking Swedish Hillfort Glass
Bruce Arey, Edward Vicenzi, Rolf Sjoblom, Robert Koestler, Paula DePriest, Thomas Lam, David Peeler, John McCloy, Albert Kruger, Jamie L. Weaver
Borborg Hillfort is a vitrified hillfort located in the Husby-Långhundra parish in Uppland Sweden (Fig. 1A). The site dates to the Great Migration Period, around 740 ± 100 CE. . Two types of glasses have been identified within the ramparts one that is rich in Si and one that is rich in Fe . Both glasses have been found on the outside surface of the walls, and have been exposed to atmosphere since their vitrification (Fig. 1B). Given these conditions, and their reported chemical compositions, the two glasses have been determined to be candidates for the study of the long-term alteration of silicate glasses in natural environments . A unique aspect of the alteration research on these samples has been the use of microscopy to identify microbial activity on the surface of the glasses. With few exceptions, the biological influence on long-term glass alteration has not been well studied. In this presented study, the surface of a specimen excavated from Broborg (Fig. 1C) was imaged in a FEI Helios NanoLab 660 (Hillsboro, OR) FIB-SEM with an Energy Dispersive Spectrometer (EDS) (EDAX Newark, NJ). An accelerating voltage of 5 keV for imaging, 10-20 keV for EDS, and a working distance of 4 mm were used in the analyses. Imaging was performed with an Everhart- Thornley secondary electron (SE) detector in field-free conditions, and through-the-lens detectors (TLD) for SE and back-scatter electron (BSE) imaging in immersion mode. Both glass and mineral sections of the sample were studied.