Carbon coating objects for SEM/EDS

The Kelsey Museum of Archaeology (a University of Michigan museum)
has recently begun a collaborative study with our Geology Department
to chemically identify the stones used for about 160 pre-historic
stone stamp seals in our collection. We are using a scanning
electron microscope fitted with energy dispersive analysis
(SEM/EDS).

The geologists usually coat their samples for SEM with carbon. As I
understand it, this helps prevent stray X-rays from nearby areas
from interfering with analysis of the particular spot you wish to
analyze. We are placing the entire seal (they are quite small) in
the SEM chamber and our analyses would be more reliable if we could
coat the seals themselves with the carbon. Does anyone have
experience doing this?

The carbon coating used here is applied by placing the sample in a
bell jar with a very thin rod of graphite and pulling a vacuum. The
graphite is, in the words of our geologist friends, "vaporized"
(although probably they mean evaporated?) and deposited on the
sample. We coated a glass slide this way, and I find that the
graphite is very easy to remove with ethanol:de-ionized water in a
1:1 ratio. I feel fairly confident that the coating can be applied
and removed without difficulty, but I would be interested to hear
from the conservation-science community any opinions/experiences in
using a coating on small objects for SEM.

Suzanne Davis
Conservator
Kelsey Museum of Archaeology


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                  Conservation DistList Instance 17:52
                 Distributed: Sunday, February 1, 2004
                       Message Id: cdl-17-52-019
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