 However, in contrast to other basic i.e.cationic dyes, Alcian blue usually (given the right pH and salt concentrations, and normal temperature and duration in minutes, not hours) preferably stains acidic glycosaminoglycans but not the chromatin and nissel substance, the mechanism of which had been a mystery for a long time and various theories were proposed.Though the presumed basis of the staining is its positive charge attracted to negative structures (e.g.