Coreopsis tinctoria Nutt. As a New Raw Material for Natural Hair Coloration: Discovering the Dyeing Potential of Chalcones

This study presents the development of a natural hair dye based on Coreopsis tinctoria Nutt. plant extract with and without subsequent mordanting. The dye molecules behind the color development have been investigated to gain better understanding of the relationship between flavonoid structure and color on hair. Yak hair was dyed under different conditions and wash fastness tests were carried out to evaluate the performance of the new hair dye. Analysis of Coreopsis tinctoria Nutt. plant extract was performed to assess the chemical constitution of hair dye. Coreopsis tinctoria Nutt. extract solely led to yellow colors (as represented within L*a*b* color space: L* = 65.5; a* = 0.7; b* = 46.6), whereas the treatment combined with ferrous lactate led to dark brown colors (L* = 26.4; a* = 2.3; b* = 10.0). Wash fastness demonstrated a very good color stability with a maximum loss in color intensity of ΔE = 12.4 after 24 hair washes. Dyeing experiments using the most abundant flavonoids marein, flavanomarein, okanin, and isookanin gave insight into the responsible flavonoids for color outcome. In combination with ferrous lactate, chalcones led to brown colors and flavanones to gray colors. The chalcone okanin presented itself as the most powerful dye, leading to intense colors in combination with ferrous lactate (ΔE = 56.6), at low dye concentrations of 0.1 mg mL−1.