On December 7, 2017, Bard Graduate Center Professors Aaron
Glass and Jennifer Mass led a research trip to the American Museum of Natural
History with students in the fall seminar course, “Native Arts of the Northwest
Coast: Ethnography, Museums and Conservation,” co-taught by Glass and BGC
Andrew W. Mellon Fellow Jessica Walthew. The students had been conducting
original research on Indigenous objects from British Columbia as part of course
work in preparation for a 2019 Focus Project exhibition on Franz Boas and early
ethnology. While most of their research focused on library and archival
resources, the students working on AMNH materials had the benefit of direct
object study.
The purpose of this visit was to
conduct portable XRF (x-ray fluorescence) testing, a non-destructive analytical
technique used to determine the elemental composition of materials. XRF testing
determines the chemistry of a surface by measuring the fluorescent (or
secondary) X-rays emitted from the object when it is excited by a primary X-ray
source—in this case, a small hand-held spectrometer visible in the accompanying
photo. Mass demonstrated the technique through analysis of five objects
requested for exhibition loan: two polychrome wooden masks, a large carved and
partially painted wooden settee back, and two engraved and pigmented copper
plaques (one visible here).
In some cases, the testing
confirmed prior assumptions. For example, traces of red pigment on the settee
proved to be vermillion (mercury sulfide), likely commercial pigment obtained
in the fur trade and common in late-nineteenth century objects from the
Northwest Coast. However, new insight was provided on every object, raising
questions for further research. We had assumed both masks were painted red with
vermillion, however they turned out to contain iron oxide (either naturally
occurring or commercial red ochre/hematite) as well as calcium. While one
mask’s black pigment showed traces of phosphorous (suggesting the use of bone
black), the other mask and the settee were painted with magnetite (black iron
oxide), a reflective pigment often mistaken for graphite. One mask has traces
of titanium on the interior surface, possible residue from the white face paint
of the dancer who wore it.
Some of the most interesting
results concerned the two coppers, neither of which are well documented in
museum records. While the one pictured above showed evidence of electrolytic
refining (which dates the sheet copper, of European manufacture, after 1850), the
other copper has traces of lead, antinomy, and tin, suggesting a less refined,
“dirty” alloy (possible evidence of a cheaper commodity form). Most
significantly, this copper was blackened with a carbon-based pigment (to which
XRF is not sensitive), likely wood pitch. However, the other one was patinated
with selenium, a common Euro-American mode of black patination in the
nineteenth century and likely evidence of a commercial, rather than strictly
Indigenous, context of manufacture. This last finding helped confirm Glass’s
hypothesis, based on iconographic and archival evidence, that the second copper
is a detailed replica (based on an illustration in one of Boas’s books)
produced within the thriving souvenir trade of the early twentieth century.
Through the cooperative
relationship of BGC and AMNH, and the scientific expertise of Mass, our
students were exposed to technical research methods that deepened our
understanding of five particular objects, raised new questions for additional
investigation, and provided detailed insight for the 2019 exhibit. We found the
encounter so gratifying that we decided to feature the XRF analysis, along with
its implications for object conservation, in the exhibition itself as a
contribution to the BGC’s larger, Mellon-funded initiative on “Cultures of
Conservation.”
-Aaron Glass and Jennifer Mass
