Disclosed are methods of preparing thiol keratin-containing materials, comprising applying a mixture comprising one or more thiol compounds and a catalyst. Methods of preparing cross-linked keratin-containing materials by applying a mixture comprising one or more thiol compounds and an oxidizing agent are also disclosed. Methods of grafting monomeric and polymeric materials on keratin-containing materials to provide a covalent coating on keratin-containing materials are disclosed. A mixture comprising one or more thiol compounds is applied to the keratin-containing material sample. The keratin-containing material sample then comprises a plurality of free thiol groups. A monomer is optionally applied to the keratin-containing material sample to form a plurality of covalent bonds between the free thiol groups and the monomers. The disclosed grafting methods can be carried out with or without catalyst.