1. Deterioration of textile or other materials caused by gradual oxidation during storage and/or exposure to light. 2. The oxidation stage of alkali-cellulose in the manufacture of viscose rayon from bleached wood pulp. 3. Originally, a process in which printed fabric was exposed to a hot, moist atmosphere. Presently, the term is applied to the treatment of printed fabric in moist steam in the absence of air. Ageing is also used for the development of certain colors in dyeing, e.g., aniline black.