Spectroscopic analysis of Turkey red oil samples as a basis for understanding historical dyed textiles

Heritage conservation science is a valuable technique for improving understanding and the preservation of historical objects. Material analysis of heritage textiles and related materials provides information about polymer and colorant degradation, and contributes to improved conservation and display practices. The re‐creation of materials following historical processes is useful for testing analytical techniques in a field where ethical constraints often limit sampling, and to also identify potential age‐related changes relative to a fresh product. Despite the broad historical interest and industrial significance of Turkey red from the late eighteenth to the nineteenth century, little about the chemical complex of these unique textiles was understood in scientific terms. This study applied modern analysis with 1H and 13C nuclear magnetic resonance (NMR) spectroscopy to investigate the conclusions reached by nineteenth century chemists, that fatty acids were a key component of the oil treatment, a unique and vital aspect of the Turkey red dyeing process. The results show that Turkey red oil samples are composed of fatty acids which tend to polymerise over time, and that modern commercial Turkey red oil has a similar composition to historical samples and a replica sample made following a nineteenth century method. This information was used to form a hypothesis for the overall Turkey red complex on the fibre, and confirmed that the experimental work of nineteenth century chemists was theoretically accurate despite their lack of precise analytical techniques. This indicates that a re‐creation and analysis approach is effective for studying heritage materials, provided the historical practice for making the original object is taken into consideration.