MCI Project Summaries 2008 - Smithsonian Institution

MCI 6205 Arlington Cemetery’s Memorial Amphitheater
MCI Staff: Carol A. Grissom, Claire Gervais, Paula T. DePriest, Robert J. Koestler, Nicole
Little, Fabien Pottier, Judy Watson, R. Jeff Speakman, Elyse Canosa, Colby Phillips, Odile
Madden
The Memorial Amphitheater at Arlington National Cemetery, made of Danby Vermont
marble (Mountain White grade) and constructed between 1915 and 1920, presented an example
of red staining. Preliminary microbiological analysis had resulted in the isolation of a redpigmented
bacterium, but in all cases stained areas were found to contain lead corrosion
products, in particular the bright orange-red minium. Scanning electron microscopy (SEM)
accompanied by energy dispersive spectrometry (EDS), X-ray diffraction (XRD) analyses, X-ray
fluorescence spectroscopy (XRF), and Raman spectroscopy revealed considerable diversity of
lead compounds in the stains, as well as in their shapes, sizes, and distribution.
Staining on the amphitheater occurs at discrete locations, most often on exterior paving
blocks between columns. The most striking example of staining, however, is located on the
outer corner of a column base to the left of the amphitheater’s stage. This area features a
Liesegang-ring-like pattern, with purple, coral red, orange, and yellow areas located sequentially
outward from the white corner. Comparison of photographs taken in 2004 and 2009 shows a net
progression of staining, with migration away from the corner and expansion of the area of yellow
washes. In-situ XRF analysis showed that the largest quantity of lead was found in purple stains
and a white area that had been purple in 2004.
Sources of lead identified near stained areas include lead sheet found in the joint above
one stained block and a lead-coated copper water-proofing membrane with a visible drip edge.
The edge is heavily corroded, with minium found in red corrosion products by XRD analysis.
Yellow stains below were found to contain the yellow lead compound litharge, also identified by
XRD. We believe that lead is present near all other stains, hidden by the stone or pointing.
Lead sheets corrode rapidly in the presence of Portland cement, which can give rise to pH
values in the pore-water of up to 13.5. At this very high pH, PbO becomes a stable oxide, as does
Pb3O4 when the environment is slightly oxidizing. Portland cement was determined to have been
used for pointing, and, thus, it is not surprising to find examples of red staining consisting of lead
corrosion products. Unfortunately, the stability of the colored lead compounds means that
removal or decolorization is unlikely to be successful.
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