Here, NaOH or NH3 · H2O is used as a precipitant or pH regulator to react with FeSO4 to form ferrous hydroxide precipitation; Air is used as oxidant; The iron sheet reacts with sulfuric acid produced during the oxidative hydrolysis of FeSO4 to provide ferrous ions required in the reaction system and maintain the pH value of the solution. The alkali consumption of acid method is less and the particles are easy to wash. The relative rates of seed preparation and crystal growth determine the particle size, particle size distribution and particle morphology of iron yellow particles.

While Skittles don't include white in their line-up, Dr. Johnson-Arbor theorizes that titanium dioxide is used to help contain all the other beautiful colors.

The National Cancer Institute tested TiO₂ for possible carcinogenicity by the oral route of exposure by feeding rats and mice with TiO₂ (size not specified) at doses 25,000 or 50,000 ppm TiO₂ for 103 weeks. They concluded that TiO₂ was not carcinogenic.Also, the study with rats fed diets containing up to 5 % TiO₂ coated mica for 130 weeks showed no treatment-related carcinogenicity. Since the size and other TiO₂ properties were not specified or determined, we cannot generalize this conclusion and we have to take into account other possible outcomes of this scenario in different exposure conditions (other size/crystalline structure of TiO₂ etc.).