A comparative study of silk dyed with traditional fermented safflower cake or dried safflower petals

This study investigates the dyeing properties of safflower red (Carthamus tinctorius) in two traditional forms—fermented dried safflower cake and dried petals—on silk textiles. Drawing on historical Chinese texts and current Japanese conservation practices, the research examines differences in the dyeing properties of the two forms. Methods such as solubility testing at various pH levels with organic solvents, colour measurement, UV-induced fluorescence imaging (UVIVF), thin-layer chromatography (TLC) and high-performance liquid chromatography with photodiode array detection (HPLC-PDA) were employed to examine differences in appearance and chemical composition of the two forms of safflower-red dye as well as the dyed silk. UVIVF revealed that safflower-red-dyed silk exhibits strong orange-red fluorescence under a 395–400nm excitation which offers a simple diagnostic tool for differentiating safflower red from other alum-mordanted natural red and purple dyes on silk. TLC using n-butanol separated six compounds in the cake-dyed silk but only five in the petal-dyed silk. TLC using ethyl acetate and methyl ethyl ketone showed two compounds were absent from petal-dyed silks compared to cake-dyed samples. Analysis of the same samples with HPLC-PDA using a reverse-phase column and sodium phosphate and acetonitrile as the mobile phase, identified 15 shared compounds, including carthamin and apigenin. Eight of these compounds appeared in significantly lower quantities in petal-dyed silk, which possibly explains the absence of the three compounds separated by TLC. The findings demonstrate differences in dyeing performance and chemical profiles when using fermented safflower cakes or dried petals to dye silk. Further investigation is required to confirm with more certainty if the two can be differentiated from analysis of safflower-red-dyed silks. The study supports the combined use of both historical and scientific methods to identify safflower red in historic textiles and offers practical tools for its analysis and conservation.