Specifies a method for determining the resistance of the colour of textiles of all kinds and in all forms to the action of a typical rubber compound such as may be used in the proofing industry, and to its decomposition products, during vulcanization in open steam, either under conditions that prevent live steam from coming into contact with the specimen to be tested (method A) or under conditions that allow live steam to infiltrate into the adjacent fabric to be tested (method B).