
1. Sheet iron method

Stability and darkening[edit]

The trend in the production of NPs is likely to lead to increasing amounts of nano-powders in the air, water and soil, which will consequently affect living organisms. Labielle et al. demonstrated that 25 % of Al(OH)3-coated TiO2 particles from sunscreens are dispersed as a stable colloid and become available to microorganisms and filter-feeders, while the remaining 75 % are probably incorporated into geogenic sediments, where they could become available to benthic fauna. Solar UV iradiation may penetrate as far as 20 m in the water column and therefore photo-activate the dispersed particles, which may have an adverse effect on various aquatic organisms.

As for titanium dioxide, the FDA approved titanium dioxide for use as a food additive in 1966. The last time the agency reviewed the additive’s safety, according to the Guardian, was in 1973.
When we purchase lithopone, we must pay attention to its ratio. This can be seen to some extent from the appearance. Basically, we can see that good products are very delicate. , and the color is also very uniform, a kind of shiny white, while inferior lithopone has uneven particles and wrong luster.
The FDA has not updated its general guidance on safety assessments since 2007. Within that time, there has been a significant increase in research on the confluence of toxicology, nanotechnology and human health. The EU updates its guidance regularly with new science available to offer proper safety assessments, with its most recent update published in 2021.