Onion Cell 1. Take a small piece of onion and using forceps (tweezers) peel off the membrane from the underside (the rough side). 2. Lay the membrane flat on the surface of a clean glass slide, and then add one drop of dye (iodine or methylene blue). Be very careful; these dyes will stain your skin and clothes. 3. Using a pin, lower a thin glass cover slip onto the slide. Make sure there are no air bubbles. 4. Put the slide onto the stage of the microscope. Make sure the objective lens is set on low power, and the microscope light is turned on. 5. Look through the eyepiece lens and turn the focusing wheel until you can see the cells. They should look like lizard skin. 6. Swap the objective lens for a high powered one so that you can see the cells at a greater magnification. You should be able to make out the nucleus.