Optimisation of purple dyeing with Mexican cochineal in cotton with multivariate analysis and the response surface method

This study aims to optimise the dyeing process of cotton fabrics using Mexican cochineal (Dactylopius coccus Costa). The objective is to obtain purple hues through the design of experiments and by using multivariate analysis. Plackett-Burman experimental designs and the response surface method were used to systematically optimise the dyeing parameters. The meta-mordanting process was the most critical factor affecting the achievement of purple hues, followed by cochineal concentration, toner concentration and dyeing time. The multivariate analysis of principal component analysis with discriminant analysis was applied to determine the significance of washing methods and toner types. Various traditional Mexican toners, including tequesquite, cardon and ash, were evaluated. The washing method was not significant, while the toner type showed a tendency towards clustering, indicating a significant effect on the dyeing process. The most recommended method was the one using tequesquite, with 20% on weight of fabric (owf) cochineal, 5% owf toner and a dyeing time of 66 minutes. Cardon was recommended as a viable toner alternative. This research provides a reproducible method for achieving desired purple shades, preserving traditional dyeing techniques from Mexican indigenous cultures.