Smithsonian Institution NMNHbl_bordergy_border




Anchorage Loan Conservation Project


Ivestigating

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NMNH_mask

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This copper rattle was part of a group of pieces purchased by George G. Heye, collector and founder of the Museum of the American Indian, now the National Museum of the American Indian, from a dealer in Los Angeles who owned a curiosity shop.  Many of the objects are made of copper or a combination of copper and other materials, and most have an aged appearance.

Copper objects like the rattle (above left) and mask (above) are anomalies in the genre of Northwest coast art. NMAI Curator Mary Jane Lenz investigated the origins of these objects, and suggested that they were possibly produced in a workshop specifically for sale. In her article, No Tourist Material, Lenz writes that Native people working in curio workshops were inspired by traditional forms and designs, but stepped outside the confines of traditional materials to produce magnificent examples of art.  She promotes the perspective that these objects are not curio art, but precursors to a great contemporary Native American art tradition.

X-ray fluorescence spectroscopy was undertaken at NMAI by Amber Davis (above) to determine the alloy composition of the metal.  Information regarding the alloy composition informs the sources of metal, be it native or acquired from contact with Russians or Europeans, and can provide insight into the object's origins.

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Two areas of bright green corrosion noted on the copper rattle looked suspiciously like a corrosion phenomenon know as "bronze disease".  Bronze disease is caused when chlorides and oxygen combine in a damp environment. These conditions are common in archaeological burials or oceanic environments, but chlorides can also be present in solutions used to create a patina on metal surfaces. Bronze disease has a powdery, bright green appearance and can be very damaging to metal objects if left untreated.

Understanding the stability of the two areas of bright green corrosion was important to preservation of the object; therefore, x-ray diffraction analysis was undertaken in collaboration with conservation scientists at the Smithsonian’s Museum Conservation Institute (above MCI staff). Analytical test results indicated the bright green corrosion was not bronze disease, pointing to the possibility of corrosion caused by an applied surface treatment, perhaps originally executed in the workshop to produce an “aged” appearance.

 
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