Textile dyeing with Indigofera tinctoria-derived dye: exploring eco-friendly processes and expanding the colour spectrum

The use of natural dyes has become increasingly important as a result of their lower environmental impact and health benefits. However, developing eco-friendly dyeing processes and auxiliary products that maintain high chromatic quality remains a challenge. Natural indigo dye exemplifies this issue, as traditional industrial reduction methods using agents such as sodium dithionite are associated with significant environmental pollution. This study explored the application of fructose as a sustainable reducing agent for dyeing cotton fabrics with indigo extracted from the Indigofera tinctoria plant, adapting an artisanal process to industrial equipment. The most effective method involved a single-stage vat dyeing process conducted at 60°C for 60 minutes, using a 1-2-3 formulation. Results indicated that fructose emerges as an effective and environmentally friendly alternative in an industrial process compared with conventional toxic reducing agents. The study also evaluated the effect of different non-toxic auxiliary products and mordanting techniques. Pre-mordanted samples exhibited more saturated colours than post-mordanted; however, wash fastness results were lower. For example, gallnut used in the pre-mordanting process produced dark tones but showed noticeable colour change after washing, while post-mordanted samples achieved higher wash fastness. The integration of diverse auxiliaries in separate dyeing processes expanded the colour spectrum beyond the conventional blue typically associated with indigo dye, introducing a range of unique shades and hues. This study contributes to the recovery of traditional knowledge, incorporating more environmentally friendly products and adapting them to industrial equipment, while exploring a diverse chromatic palette. Such innovation supports fashion designers in creating distinctive and environmentally responsible collections.