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Oxygen Isotope Fractionations during Silk Formation and Production Foundations for Interpretations of Isotope Signatures
Hong Yang, Yang Zhou, Qin Leng, Feng Zhao, Weiguo Liu

1 Laboratory for Terrestrial Environments, Department of Science and Technology, College of Arts and Sciences, Bryant University, 1150 Douglas Pike, Smithfield, RI 02917, U.S.A.
2 China National Silk Museum, 73-1 Yuhuangshan Road, Hangzhou 310002, People’s Republic of China
3 State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Science, 97 Yanxiang Road, Xi'an, 710061, P.R. China

A better understanding of the origins of ancient silk textiles along the “Silk Road” is a key to interpret cultural and trade exchanges between East and West. However, to distinguish provenance of ancient silk textiles using stable isotope analysis is only in its infancy stage with the challenge of limited baseline data for comparison as well as the lack of controlled experimental data on isotope fractionations during silk formation and production. We traced the change of oxygen isotope compositions from source water to silk products in several areas across different hydrological regimes where major silk production proliferate both in modern and ancient times in China. Oxygen isotope compositions were measured from sample series (water, mulberry leaf, silk cocoon, raw silk, and silk products) with known origins. We found that the largest apparent oxygen isotope fractionation (ε), up to 25‰ toward positive, occurs between the source water and mulberry leaves. Smaller negative Isotope fractionations due to silk worm metabolism (ε ~4‰) and raw silk production (ε ~2‰) tend to be cancelled by subsequent positive fractionations during the final stages of silk production and degradation. Large net isotope effects (Δ18O ~10‰) were observed in silk products originated between China’s wet and humid east coast and the dry and high evaporative inland areas due to the impact of different hydrological conditions. Our study represents the first attempt to systematically understand oxygen isotope fractionations during silk production and to establish oxygen isotope baseline data in silk products originated from different climatic regimes using controlled sample series. Our results bear significant implications for the interpretation of oxygen isotope signatures in ancient silk products, and such geographic variations of oxygen isotope compositions in silk products demonstrate that oxygen isotope signals can potentially be used to identify ancient silk textiles made with raw silk material originated from different climatic conditions.


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