iodine compounds can be used in x-rays because x-rays cannot go through them easily. some metals are purified using their iodides. silver iodide is used in photographic film and cloud seeding. erythrosine is a food coloring that has iodine in it. iodine can be used to make illegal drugs so it is restricted in some areas. iodine can be used as a test for reducing agents. iodine turns colorless when mixed with a reducing agent. iodine also turns black when mixed with starch. iodides become colored when mixed with oxidizing agents.