Friday, June 30, 2017

Following a trail of galena and cerussite mineral flakes to track Zuni and Pueblo potters from AD 1275 - AD 1670

Southwestern North America (D. Rumsey Collection)

I am an archaeologist who uses lead isotope analysis to source the ores used to make glaze paints on pre-contact and early historic Pueblo glaze painted pottery.”, was the introductory sentence of an e-mail received by Brad Johnson, Arizona Geological Survey (AZGS)  research scientist, on 15 April (tax day) 2017. 

Archaeologist Judith Habicht Mauche, University of California at Santa Cruz, expressed her interest in expanding her research on lead-glazed paints and pigments of the Zuni and Pueblo potters of New Mexico to the upper Little Colorado River of north-central Arizona. In e-mailing Brad, she hoped that AZGS could supply a suite of lead-rich minerals from Arizona’s metallic mineral districts sampling. 

She came to the right place. For the past year, AZGS staff curated the assets of the Arizona Mining, Mineral and Natural Resources Museum (MMNRE). Including more than 21,000 mineral specimens from the collection of the former Arizona Mining and Mineral Museum; ~ 35% of those minerals (~ 8,000 specimens) originated in Arizona’s metallic mineral districts (Carter and Conway, 2017)

Dr. Habicht Mauche’s primary interest was in common lead ore minerals galena (PbS) and cerussite (PbCO3).  Mineral curator Catie Carter scavenged nearly 50 specimens for Dr. Habicht Mauche to sample. Sampling involves scraping the face of the mineral with a small carving knife with a disposable blade, changed out after each mineral to avoid contamination. A minute shower of mineral flakes is captured on paper, which is then folded and placed in a sealed and numbered plastic envelope for later lead isotope analysis. (Museum quality galena and cerussite were not provided in the sample set.) 

From about AD 1275 to the 1700s, indigenous people of the Southwest included lead flakes in glaze and paint pigments. The practice ended about AD 1680, at the time of the Pueblo Revolt when the Pueblo Indians drove the Spanish from New Mexico (then the province of Santa Fe de Nuevo México).  

As Juliet explains in the accompanying video, ‘Getting the lead out! Using Pb isotopes to track Native American lead glaze technology’, lead glazing and pigment technology originated in the upper Little Colorado River before migrating east and south into the Rio Grande valley of southern New Mexico.  

The lead isotope fingerprint of individual galena and cerussite ore deposits is unique. So matching isotopes from the mineral source with lead isotopic signatures of the paints or pigments pinpoints the source area. According to Dr. Habicht Mauche, by examining the concentration of lead, copper and manganese, ‘we can see specific paint recipes and we can see how those specific paint recipes moved from one area to another.’ The working hypothesis: paint recipes were specific to particular groups of people. Fingerprinting the source of the lead provides archaeologist with a tool for tracking technology transfer across the SW U.S. Thereby shedding light on migration or trade patterns of the Zuni and Pueblo people of the Southwest.

Carter, C.S. and Conway, F.M., 2017, Mineral, Mining Artifacts, and Physical Assets of the former Arizona Mining and Mineral Museum. Arizona Geological Survey Open-File Report OFR-17-02 v 1.1, 24 p.

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