Room-temperature electrolytic coloration and spectral properties of natural fibrous gypsum using a pointed anode

Electrolysis experiments can be performed at room temperature and under various voltages using natural fibrous (NF) gypsum with a pointed anode and a flat cathode. The NF gypsum is colored electrolytically. SO4−, SO3−, SO2−, O3− and O− defect centers are produced in colored NF gypsum. The characteristic absorption bands of the defect centers are observed in the absorption spectra of the colored NF gypsum. The defect centers come mainly from electric-field-induced decomposition and/or direct electron loss of SO42− radicals. Current is measured during electrolytic coloration. Electron exchanges from electron and charged radicals to electrodes induce complete current.