Plant fiber textile yarns with copper carbonate encrustations: Dating and chemical analysis
Document Type
Book Chapter
Publication Date
2023
Department/School
Chemistry
Publication Title
Chemistry in the Service of Archaeology
Abstract
Fragments of fabric made of plant stem fiber excavated from the Seip Mound Complex in Ohio (ca. 2100–1500 BP) show green coloration in repeating patterns of decoration. It remains unclear how the material was decorated, whether it was painted, stained, or prepared using some kind of resist-dyeing process. Minute samples taken from small bits of yarn that have fallen away from the fabric fragments were provided by the Ohio History Connection Museum to determine if a binding medium could be identified in the green staining, and to develop a minimally destructive approach to measure the radiocarbon age. To facilitate this study, we prepared mockups of potential binding media and copper carbonate pigment on milkweed fibers and built a database of their compositions based on our examination with direct analysis in real time mass spectrometry (DART-MS). Plasma-chemical oxidation (PCO) can be used as a minimally destructive process to prepare organic materials, like plant fibers, for accelerator mass spectrometric (AMS) radiocarbon analysis. PCO uses a low-temperature chemical reaction between excited oxygen species in the plasma and the cellulose in the plant fibers to produce carbon dioxide for dating. During PCO preparation of the plant fiber yarn fragments that showed green staining from copper carbonate minerals, it was found that argon plasmas decomposed the copper carbonate through an as yet poorly understood mechanism. We present here the development of appropriate wet-chemical pretreatments and investigations into the decomposition of copper carbonate pigments under the plasma conditions. One of the results of these studies is a protocol by which further studies of these and other textile fragments can be directly radiocarbon dated in a manner that preserves these precious objects for future study and appreciation.
Recommended Citation
Wilson, B., Peterkin, I., Repaska, M., Jakes, K., Southon, J., & Armitage, R. A. (2023). Plant fiber textile yarns with copper carbonate encrustations: Dating and chemical analysis. In R. A. Armitage & D. Fraser (Eds.), Chemistry in the service of archaeology (pp. 121–139). American Chemical Society. https://doi.org/10.1021/bk-2023-1446.ch006
Comments
R. A. Armitage is a faculty member in EMU's Department of Chemistry.
*B. Wilson, I. Peterkin, and M. Repaska are EMU students.