An introduction is given for technical discussions of dyes and dyeing, cleaning and conserving old and weak fabrics. Fibers are classified as vegetable or cellulosic and animal or protein. Several fibers of interest to the conservator are listed and described as regards their physical and chemical characteristics. Methods of identification of fibers are discussed and idealized sketches of six fibers are shown. A table of characteristics of the most common ancient fibers provides a key for their recognition as well as a chart of their behaviour in the presence of chemicals and destructive reagents.