Alcian blue, also known as Aixian blue or Alcian blue, is a copper-titanium anthocyanine conjugate dye, initially used for textile fiber dyeing. This cationic dye combines with acidic groups, i.e., Alcian blue forms insoluble complexes with anionic groups such as carboxyl and sulfate contained in tissues, and Alcian blue consists of a central copper-containing phthalocyanine ring and four isothioureas linked by a thioether bond, which is moderately basic and gives Alcian blue a cationic character. The isothiourea group is moderately basic, making Alisin Blue cationic. pH 2.5, the carboxyl group in the tissue ionizes, carries a negative charge, and forms a salt bond with the cation in Alisin Blue, staining acidic mucus substances with carboxyl groups (mucin sulfate and salivary mucin); pH 1.0, the sulfate in the tissue ionizes, carries a negative charge, and forms a salt bond with the cation in Alisin Blue, staining the tissue with sulfate. causes tissues with sulfate (e.g., sulfated mucus material) to stain.

Cartilage staining solution (Alisin blue method, pH 2.5) can distinguish the class of mucus material by using different pH values of the staining solution. At pH 1, carboxylic acid group (-COOH) does not stain, and sulfate group (-OSO3H) stains; at pH 2.5, carboxylic acid group stains well and sulfate mucus does not stain well, which causes sulfate and salivary mucus proteins to stain.