Each group needs:

• test tube or other thin-walled, tall and clear vessel
• enough oil to fill the vessel nearly to the top (such as any cooking oil)
• eye dropper
• several 4-8 oz (118-236 mL) cups
• water (enough to fill ¾ of each cup)
• food coloring (a couple of drops per water cup; water-based food coloring recommended)
• liquid dish soap (a few mL at most)