pyrroloquinoline

This article discusses the discovery of phosphorescent lithopone on watercolor drawings by American artist John La Farge dated between 1890 and 1905 and the history of lithopone in the pigment industry in the late 19th and early 20th centuries. Despite having many desirable qualities for use in white watercolor or oil paints, the development of lithopone as an artists' pigment was hampered by its tendency to darken in sunlight. Its availability to, and adoption by, artists remain unclear, as colormen's trade catalogs were generally not explicit in describing white pigments as containing lithopone. Further, lithopone may be mistaken for lead white during visual examination and its short-lived phosphorescence can be easily missed by the uninformed observer. Phosphorescent lithopone has been documented on only one other work-to-date: a watercolor by Van Gogh. In addition to the history of lithopone's manufacture, the article details the mechanism for its phosphorescence and its identification aided by Raman spectroscopy and spectrofluorimetry.

Lithopone, C.I. Pigment White 5, is a mixture of inorganic compounds, widely used as a white pigment powder. It is composed of a mixture of barium sulfate and zinc sulfide. These insoluble compounds blend well with organic compounds and confer opacity. It was made popular by the cheap production costs, greater coverage. Related white pigments include titanium dioxide, zinc oxide (zinc white), zinc sulfide, and white lead.

We’re most often exposed to E171 through the foods we ingest. We find E171 in many food products, like popsicles, ice cream, gum, and more. Another way we ingest E171 is through pharmaceutical drugs. Many pills and capsules contain E171 as an inactive ingredient.  

Titanium dioxide is predominantly used as a pigment in products such as paints, coatings, plastics, food, cosmetics, and paper. The ability of TiO2 to scatter light and provide a white color makes it an essential ingredient in achieving high-quality finishes in these applications. However, the production of titanium dioxide can be complex and costly, given that it involves raw materials such as ilmenite and rutile, as well as advanced processing technologies. Manufacturers are continuously striving to optimize costs without compromising quality, making the search for affordable suppliers a top priority for many businesses.

As of August 7, the use of titanium dioxide in food is banned in the European Union. Europe is taking a precautionary principle approach based on findings from the European Food Safety Authority (EFSA).

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.