Freshmen in the McIntosh STEM Program performed a Gram Stain Technique Lab to determine cell wall structure in their Gifted Biology class. In the lab, bacteria are first smeared onto a microscope slide. The slide is then flooded with a purple dye known as crystal violet. After rinsing, the slide is filled with iodine, which helps fix the dye onto the bacteria. The slide is rinsed again, and is then filled with acetone. Finally, the slide is rinsed one more time and then stained with a pink dye known as safranin. Under the microscope, if the bacteria retain a purple color, they are gram-positive, while those that turn pink are gram-negative.