Example: East Java Mosaic Glass Beads
Above: A backscattered-electron (BSE) image of the surface of a polychromatic East Java mosaic bead. The bright areas corresponds to a glass that contains lead as an opacifier. The field of view is 3 x 4 millimeters.
East Java mosaic beads are not only found in Java but also Malaysia, the Philippines, Sumatra, and Kilimantan. These beads are among the heirloom items on the island of Palau and were used as a form of currency. They were principally made in eastern and central Java, Indonesia from about 900 to 1300 CE. These polychromatic beads, as shown below, are sometimes called Jatim beads, a combination of the terms Java and Timur, meaning "East." Such beads seem to have influenced by Roman and Middle Eastern bead- and glass-making techniques. The beads have interest from technological, economic, exchange, and cultural-transmission perspectives.
As a result of these interests, the beads' manufacture and raw materials are subjects of study. Manufacturing a mosaic bead involves multiple steps -- a glassworker starts by making several components, and the preformed parts then are used to form and decorate the finished bead. The beads have a wound core that is covered by thin slices of patterned glass rods -- colored glass rods were bundled, heat-softened, stretch-fused, and then sectioned to produce glass tiles with the same colorful design. One focus of research is identifying the raw materials that ancient Javanese glassmakers used to made the different colored glasses. I used electron microprobe analysis to analyze the glasses, investigate glass interfaces, and identify minerals within the glasses used as opacifiers and colorants. The intent is to learn more about ancient materials selection, exchange, and processing on these islands.
Above: A close-up of the backscattered-electron image at the top of this page; image is about 3 mm across.
Below: The BSE image and five element maps show the interface between two glasses. One glass used lead oxide as an opacifier, and the glasses differ in their soda (Na) and lime (Ca) contents. The chemical compositions of these two glasses can be determined, and the minerals used as opacifiers and colorants in the glass can also be identified and chemically analyzed, allowing raw-material identifications. The field of view is about 2 x 2 mm.
8/24/07
Added:
Electron Microprobe Analysis in Archaeology
Electron microprobe analysis (EMPA), also known as electron probe microanalysis (EPMA), is an analytical technique that combines scanning electron microscopy (SEM) and compositional analysis using x-ray spectrometry. The ability to determine structure and chemistry of samples makes EMPA very versatile. This is a dominant analytical technique in geology, but it is not as commonly used in archaeology despite similar materials in studied both fields. Here I will post about topics in EMPA, artifacts I have analyzed, archaeological studies that use EMPA, etc. If there is a topic you'd like to see posted here, please let me know.
Ellery Frahm
Doctoral Candidate, Archaeology
Research Fellow, Geology & Geophysics
University of Minnesota - Twin Cities
BSE
Al
Ca
Na
Pb
Si
