Optimization of repetitive dyeing on CVC yarn with merbau ( <i>Intsia bijuga</i> ) bark extract

Purpose This study aims to evaluate and optimize the number of immersion cycles required to effectively dye CVC (Chief Value Cotton) yarn with a Merbau (Intsia bijuga) bark extract, using alum and FeSO4 as mordants. Design/methodology/approach The dyeing process for CVC yarn with Merbau dye was divided into five stages: scouring, pre-mordanting, dyeing, post-mordanting and washing. During the dyeing stage, the yarn was repeatedly immersed in the dye bath and oven-dried in cycles up to six repetitions. Observations were made after each cycle using gravimetric and colorimetric analysis, tracking changes in the yarn from its scoured state through its post-mordanted and washed state. The optimal dyeing condition was defined as the point at which further cycles produced no significant differences in the yarn’s weight or color values, even after washing with detergent. Findings Repetitive dyeing proved to be an effective approach for achieving and controlling the desired color shade, particularly when using natural Merbau dye with a mordant. Using a 5% alum mordant, Merbau-dyed CVC yarn required four immersion cycles to achieve good wash fastness. With a 10% FeSO4 mordant, the yarn became darker and required five immersion cycles to minimize color fading after washing. Furthermore, yarn that underwent FeSO4 post-mordanting developed a darker hue due to the inherent color of the iron complex. Practical implications The results provide preliminary data on applying Merbau dye in textile coloring and demonstrate how to avoid excessive dyeing process or mordant use without compromising the shade or quality of the dyed fabric. Implementing these findings can maintain fabric color quality while reducing needless steps in the dyeing process. This guidance is particularly useful for home and small-scale textile industries, supporting the sustainable use of natural dyes in the future. Originality/value This study defines the optimal number of dye immersion cycles for industrial application of Merbau dye on CVC yarn, considering two different mordants at specified concentrations. By determining this optimum condition, the work addresses a practical knowledge gap, enabling more efficient use of natural dyes for consistent results in textile coloring.