Bacterial smear is taken. It is then air dried. Then, it is stained with crystal violet/gentian violet for 30 seconds. Bacteria acquire bluish-purple coolour due to stain. It is then washed with water which is followed by iodine staining (0.5 percent solution). There will be a formation of CVI (Crystal Violet Iodine) complex. It is then treated with alcohol. The bacteria that retain the stain are gram positive. The destained bacteria are subjected to counter staining with safranin. If pink colour appears, the bacterium is gram negative.