Describes a method for determining the resistance of the colour of textiles in all forms to manufacturing operation designed to remove vegetable impurities by treatment with the cited chemical at high temperatures. The method is mainly applicable to wool and textiles containing wool, particularly those containing also acetate or polyamide fibres. The treated specimen is dried, baked, rinsed and neutralized. The changes in colour after rinsing, neutralizing and drying are assessed with the grey scale.