The electron probe microanalyzer can determine the elemental composition of extremely small samples of materials, such as metal, stone, ceramic, glass, and pigments. A narrow beam of electrons is scanned over the specimen to produce an image of the surface and a map of the spatial distribution of all elements in the periodic table except hydrogen, helium, and lithium. The microprobe is also used to quantitatively determine the chemical composition of very small spots (1 micron) on the sample surface, down to a limit of 50 parts per million.

Applications:

	A more detailed view of the GCI's EPMA, with the door to the sample chamber open. Photo: Jeffrey Levin.

The history of an object is often preserved in its outer skin, which can be investigated with the electron microprobe. Examples of the application of this technique include:

• mapping the distribution of alteration components in cross sections (e.g. calcium oxalate patinas on marble);
• quantifying the glaze composition of ancient Greek vases;
• characterizing weathered stone surfaces;
• analyzing outdoor bronze patinas;
• quantifying the composition of historic pigments and glass;
• determining the composition of ancient silver and gold objects;
• identifying rock art pigments.

Further reading:

Walton, M.S., Doehne, E., Trentelman, K., Chiari, G., Maish, J., and Buxbaum, A. (2008). Characterization of coral red slips on Greek Attic pottery. Archaeometry 50, 10.1111/j.1475-4754.2008.00413.x.

Marchesi, V., Messiga, B., and Riccardi, M.P. (2005). Window panes of the Certosa di Pavia: Chemical composition, microstructure and alteration. Surface Engineering 21, 397-401.

Doehne, E., and Ma, Q. (2004). Rediscovering Ancient Technology: Microbeam Analysis of Han Purple. Microscopy and Microanalysis 10, 910-11.

Corzo, M.A., D. Stulik, E. Doehne and A. Wallert. "Scientific Analysis of a Fayum Portrait by the Getty Conservation Institute." In Portraits and Masks: Burial Customs in Roman Egypt, edited by M.L. Bierbrier. London: 1997.

Doehne, E. "Evaluation of Tesserae from the Paphos Mosaics." The Conservation of the Orpheus Mosaic at Paphos, Cyprus. Los Angeles: The J. Paul Getty Trust, 1991.

Doehne, E., Podany, J., & Showers, W. "Analysis of weathered dolomitic marble from Thasos, Greece." Acta Archaeologica Lovaniensia - Monographiae 4, 614: 213-227; Ancient Stones: Quarrying, Trade and Provenance; Marc Waelkens, Norman Herz and Luc Moens eds.; Leuven University Press, 1990.

Scott, David A. & Eric Doehne. "Soldering with gold alloys in ancient South-America -- Examination of small gold studs from Ecuador." Archaeometry 32 (1990): 183-190.

A basic explanation of EPMA by the New Mexico Bureau of Geology and Mineral Resources can be found here.