Tales unraveled through threads: Exploring the influence of natural dyes on the carbon and nitrogen isotope ratios of wool fibers from historical rugs

Abstract

EA-IRMS has been used to find isotope ratio patterns as a way of ascertaining the provenance of materials in several fields of science. In this work, EA-IRMS analysis of δ13C and δ15N was used to study historical rugs’ raw materials. The influence of chromophores in the isotope ratio of wool was studied by dyeing contemporary wool with traditional dyestuff and analyzing it by EA-IRMS. Additionally, aiming towards provenance determination, historical rugs’ samples were analyzed. In general, δ13C and δ15N of contemporary dyed wool showed no significant difference between samples (P > 0.05) which rebutted the hypothesis that chromophore isotope ratios influence those of wool. Furthermore, δ13C and δ15N of both contemporary and historical wool samples were indicative of sheep diets comprised exclusively of C3 unfertilized plants. Exception was made for one rug whose δ15N values were compatible with organically fertilized plants. Particularly, δ13C and δ15N ratios of historical samples showed significant inter-rugs differences (P < 0.05) which could evidence meteorological changes over the years. Intra-rug differences detected in only one of the three rugs studied could be linked to changes in sheep diet and pastures management practices due to drought conditions. In sum, this work's results showed that is possible to use EA-IRMS analysis of δ13C and δ15N to study dyed wool without chromophore interference.