The common thread: authenticating a Nazca tunic using combined dye analysis by LCMS and radiocarbon dating on a single yarn

Description:
Accessioning ancient textiles into museum collections often requires objective information regarding the object’s appropriateness and authenticity before purchase. In the case of dyed fibers, evidence of period appropriate dyestuffs builds confidence and reduces the chances of the object being a simple fake produced using modern materials. Increasingly chronometric age estimates in the form of radiocarbon dating are needed to further prove that the naturally occurring materials match the purported date of the textile. Each of these techniques typically consumes a small sample of the object, and normally they are conducted separately by different laboratories on individual samples. Although each analysis requires only a small yarn, repeated sampling can endanger the structure of a woven textile.

In 2020, the Indianapolis Museum of Art at Newfields sought to acquire a Nazca dyed camelid wool tunic dated to the period 100 BCE – 600 CE. Because of the supple feel and excellent condition of the artifact, concerns were raised internally over its purported age. This report demonstrates for the first time the analysis of dyes by liquid chromatography-diode array detection-mass spectrometry (LC-DAD-MS) and subsequent 14C dating of the extracted yarns. The chemicals and labware used in the dye extraction (solvents, oxalic acid, HF) do not contaminate the fibers with exogenous carbon. Reusing the extracted yarns from dye analysis for radiocarbon dating reduced the risk of additional damage to the textile. The analysis confirmed that the wool fibers were dyed with South American plant-based dyestuffs (anthraquinones, inidgoids, flavanoids), and the fibers were dated between 595 and 665 CE, viz. the Late Nazca Period. Based on these confirmatory findings, the tunic was accessioned into the collection in 2021, and its tombstone information in the museum records was modified to reflect the experimental results.

Speaker: Gregory Smith - Indianapolis Museum of Art at Newfields
Dr. Smith designed, outfitted, and now operates the conservation science laboratory at the Indianapolis Museum of Art at Newfields where he conducts technical studies of the museum’s collections. His research interests include undergraduate education at the Arts-Science interface, assessing pollution off-gassing of museum construction materials, and understanding the chemical degradation of artists’ materials. Dr. Smith was selected by the American Institute for Conservation (AIC) to receive their National Advocacy Award in 2018 for his work in public lecturing and curating exhibitions that focus on the role of Science in the Arts.