Conservation-themed Visit to the American Museum of Natural History

posted on 29 Mar 2018 06:46 by swang
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Originally published in the BGC Newsletter.

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

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