Carbol Fuchsin Application: The primary stain, carbol fuchsin, is applied to the sample and heated to facilitate penetration of the dye into the cell walls of acid-fast bacteria. Decolorization: The sample is then treated with an acid-alcohol solution. Acid-fast bacteria retain the red color of the carbol fuchsin, while non-acid-fast cells do not. Counterstain: Methylene blue or another counterstain is applied to provide a contrasting background. Non-acid-fast cells will take up the counterstain and appear blue or green.
