In the laboratory, a heat- fixed smear of bacteria is stained with crystal violet for one minute. Then, iodine,which acts as a mordant, is added to the smear for one minute, and the remainder is washed free. All bacteria are now blue- purple. Alcohol decolorizer is added to the slide until the free stain is removed. In this step, the Gram- negative bacteria lose the blue- purple dye, but Gram- positive bacteria retain the dye and remain blue- purple. In the fourth step, the red dye safranin is added to the smear. The Gramnegative bacteria will accept the dye and become red- pink, while the Gram- positive bacteria remain blue- purple. At the conclusion of the procedure, the stains are examined under the microscope and the color of the bacteria reveals the Gram reaction.