Although barium sulfate is almost completely inert, zinc sulfide degrades upon exposure to UV light, leading to darkening of the pigment. The severity of this UV reaction is dependent on a combination of two factors; how much zinc sulfide makes up the pigments formulation, and its total accumulated UV exposure. Depending on these factors the pigment itself can vary in shade over time, ranging from pure white all the way to grey or even black. To suppress this effect, a dopant may be used, such as a small amount of cobalt salts, which would be added to the formulation. This process creates cobalt-doped zinc sulfide. The cobalt salts help to stabilize zinc sulfide so it will not have as severe a reaction to UV exposure.
In food, titanium dioxide has a few different uses. Most notably, its food-grade form is used as a colorant to enhance and brighten the color of white foods such as dairy products, candy, frosting, and the powder on donuts. For foods that are sensitive to UV light, titanium dioxide is used for food safety purposes to prevent spoilage and increase the shelf life of food.
Despite a bullish trends ruling the market for the bulk of the period, the North American market had mixed sentiments in the fourth quarter of 2021. This was mostly due to the adequate pushback from the supply-demand imbalance, which was further compounded by rising natural gas prices, which had taken a proper toll on the future production of numerous minerals, including titanium dioxide. An increase in COVID instances had prompted concerns in ore feedstock. As a result, during the fourth quarter of 2021, the FD UGSC (USA) quarterly average negotiations for the chemical CP Rutile Grade were finalised at USD 4434 per tonne.