In a scanning electron microscope (SEM), the image of an object is formed using a beam of electrons rather than visible light. The SEM can magnify objects 100,000 times or more and produce detailed three-dimensional images. The environmental scanning electron microscope (ESEM) has the capabilities of the SEM—and one critical advantage.

	A more detailed view of the GCI's ESEM. Photo: Jeffrey Levin.

With the SEM, the sample must be in a vacuum; the ESEM is designed to operate at much higher pressures, allowing imaging of uncoated samples and even liquids. The ESEM's internal environment can be changed to allow dynamic studies of phenomena such as corrosion and salt crystallization. With the addition of time-lapse video, scientists can cycle temperature or humidity conditions and observe changes over time.

Applications:

	Carson removing from the ESEM a sample that he has just analyzed. Photo: Jeffrey Levin.

The ESEM has been useful in studying the wall paintings at the Mogao grottoes in China and in examining the distribution of salts in mud plasters. For Prague's St. Vitus mosaic, the ESEM was used to investigate the corrosion layer on the tesserae, to study methods of removing corrosion products, and to conduct failure analysis of several protective coatings tested for use on the glass mosaic. Because the ESEM allows dynamic studies, it was used to investigate the response of samples of the Dead Sea Scrolls to fluctuation in relative humidity.

Other uses include:

• determining the elemental composition of paint in cross-sections;
• direct examination of swelling and shrinkage of clay in adobe;
• dynamic study of corrosion on lead exposed to formaldehyde vapors;
• salt crystallization and its impact on building stone.

Further reading:

Doehne, Eric, and Dusan C. Stulik. "Applications of the Environmental Scanning Electron Microscope (E-SEM) to Conservation Science." Scanning Microscopy 4, no. 2 (1989): 275-286.

Bower, N.W., D.C. Stulik, and E. Doehne. "A critical evaluation of the environmental scanning electron microscope for the analysis of paint fragments in art conservation." Fresenius' Journal of Analytical Chemistry 348 (Spring 1994): 402-410.

Doehne, Eric. "ESEM development and application in cultural heritage conservation." In In-situ Microscopy in Materials Research, edited by Pratibha L. Gai. Kluwer Academic Publishers, 1997.

Doehne, Eric. "A new correction method for high-resolution energy-dispersive X-ray analyses in the environmental scanning electron microscope." Scanning 19 (1997): 75-78.

Rodríguez Navarro, C., Sebastian, E., Doehne, E. & Ginell, W.S. "The role of sepiolite-palygorskite in the decay of ancient Egyptian limestone sculptures." Clays and Clay Minerals 46 (1998): 414.

Rodríguez Navarro, Carlos, & Doehne, Eric. "Salt weathering: Influence of evaporation rate, supersaturation and crystallization pattern." Earth Surface Processes and Landforms 24 (1999): 191-209.

Rodríguez Navarro, Carlos & Doehne, Eric. "Time-lapse video and ESEM microscopy: Integrated tools for understanding processes in-situ." American Laboratory 31 (May 1999): 28-35.