Assessment of Tagetes erecta L. natural dyeing capabilities on Eri silk by utilization of a bio-mordant

Purpose This study aims to evaluate the dyeing potential of Tagetes erecta L. extract on Eri silk and examine the effectiveness of Emblica officinalis as a plant-based bio-mordant. Design/methodology/approach Dye extraction was optimized from dried marigold petals by varying material-to-liquor ratio (MLR), temperature and pH. Pre-mordanted Eri silk fabrics were dyed under acidic, neutral and alkaline conditions at controlled temperatures and durations. Color properties were assessed using CIE Lab* and Kubelka–Munk analyses. Dye–fiber interactions and surface morphology were examined using Fourier transform infrared (FTIR) and SEM, while UV–visible spectroscopy was used to evaluate UV absorption behavior. Findings An MLR of 1:10 and extraction at 75°C for 60 min were identified as optimal for dye extraction. Acidic dye baths combined with bio-mordanting significantly enhanced dye uptake, producing bright yellow shades with the highest K/S values (up to 2.98). Bio-mordanted samples showed improved wash and light fastness (ratings 3–4). FTIR spectra revealed a shift in the amide I band, indicating strengthened hydrogen bonding between dye molecules and silk fibroin. SEM images confirmed uniform pigment deposition, and UV–vis analysis demonstrated enhanced UV absorption in bio-mordanted fibers. Practical implications The marigold–bio-mordant system provides a sustainable alternative to synthetic dyes and metal mordants for protein-based textiles, enabling eco-friendly processing and value addition to Eri silk using renewable plant resources. Originality/value This work demonstrates the synergistic use of marigold dye and a plant-derived bio-mordant for the first time on protein-based fiber Eri silk to achieve improved color strength, fastness and functional performance, supporting the adoption of natural dyeing systems in sustainable textile production.