4. Making the slides Onion Slide Check slide Carefully peal a thin layer for the onion Using a cotton bud scrap the area Lay the thin layer onto the slide Swipe the area with the cotton bud Add a drop of Iodine to the onion Add methylene blue to the check cells Use paper towel to blot off excess then add cover slip Use paper towel to blot off excess then add cover slip Carefully lower the cover slide Carefully lower the cover slide