Cysteic acid is one of the oxidation products of the amino acids cystine and cysteine. The cysteic acid content of raw wool is normally very low. It increases with photochemical degradation (weathering). Finishing processes such as bleaching or chlorination always result in an increase in cysteic acid. The severity of any kind of oxidation may be determined directly by quantitative determination of cysteic acid. Applicable to all-wool textiles in any form before and after dyeing - for example, loose wool, sliver, slubbing, yarn or fabric.