Dyeing Condition-Dependent Metal Complex Formation in Madder and Its Derivatives: Effects on Lightfastness and Color Properties

In this study, we focused on the formation of metal complexes with dyes and investigated the relationship between dyeing procedures and lightfastness. We investigated the lightfastness of dyed materials containing alizarin and purpurin―key dye components of madder―under different mordant and dyeing conditions. The stability of the examined dyes under light exposure depended strongly on the type of metal mordant used and the pH of the dyeing environment. These results indicate that dye–metal complex formation depends strongly on the dyeing conditions, and in turn, affects the lightfastness of the dyed materials. Variations in complex formation behaviors were reflected in the fluorescence emission spectra of the examined dyes. Although natural dyes are generally considered to have poor lightfastness, our results demonstrated that the formation of dye–metal complexes can substantially enhance their photostability. Therefore, careful selection and optimization of the dyeing method and conditions could help design a suitable strategy for improving the lightfastness of natural dyes.