Lithopone, a historic white pigment, bridges art and science with its innovative origins and wide-ranging applications. Initially developed in the 19th century as a safer alternative to toxic lead-based whites, lithopone revolutionized painting and industrial use with its brilliance and opacity. However, the pigment&#;s early adoption was hindered by its tendency to darken under light exposure&#;a phenomenon that led to its historical stigma. This limitation was largely addressed in the 20th century through advancements such as cobalt doping and other stabilization techniques, significantly improving lithopone&#;s durability and lightfastness. Today, lithopone is a testament to material innovation, offering artists and conservationists a versatile tool for modern and historical applications.
Lithopone was developed in the s during a search for safer and more economical white pigments. Early industrial processes involved combining barium sulfide and zinc sulfate solutions, yielding a precipitate of barium sulfate (BaSO&#;) and zinc sulfide (ZnS). Initially, lithopone was used primarily as a filler pigment for paints, but its high opacity and bright white tone soon attracted the attention of artists and manufacturers.
By the late 19th century, lithopone had gained popularity as a replacement for white lead, which darkened over time due to sulfurous reactions. Its use flourished in early 20th-century art and decorative coatings. Paintings such as Van Gogh&#;s Les Bretonnes et le Pardon de Pont Aven have been found to contain lithopone, highlighting its adoption by significant artists of the period.
Lithopone&#;s composition is a carefully engineered mixture of BaSO&#; and ZnS. The typical formulation consists of 70% barium sulfate and 30% zinc sulfide, resulting in a dense, brilliant white powder. This unique combination imparts excellent opacity, durability, and a neutral color balance, making it ideal for various applications.
The composition of lithopone underscores its superiority in specific applications. Ideally, prepared lithopone consists of 30 to 32 percent sulfide of zinc, and a negligible percentage of zinc oxide (1.5%), with the remaining majority being barium sulfate. These attributes render lithopone nearly comparable to the best grades of French process zinc oxide in terms of whiteness. Furthermore, its oil absorption, which sits between lead carbonate and zinc oxide, solidifies its position as a functional and efficient white pigment.
In terms of application, meticulous preparation and attention to detail yield the best results. For paint grinders, maintaining a ratio of 12 pounds of refined linseed oil to 88 pounds of lithopone pigment will provide optimal workability. A salient factor that should be heeded is the state of the lithopone before mixing with oil; the material must be sufficiently dry. Only then will it integrate seamlessly with the oil, ensuring that the resultant mixture possesses the desired consistency and properties.
Lithopone&#;s historical significance is further accentuated by the advancements and modifications that followed its inception. The patent by J.B. Orr, for instance, ushered in a new white pigment&#;Orr&#;s Zinc White. This innovation was attained by co-precipitating zinc sulfate and barium sulfide, followed by a calcination process. Further refinements marked the subsequent decades, the most notable being the enhancement of lightfastness achieved in the s by introducing small amounts of cobalt salts before calcination.
While lithopone and anatase titanium white gained traction between the s and s, by the advent of the First World War, rutile titanium white had started to overshadow them. Their significance in the artist&#;s palette has since dwindled, and their use as an artist&#;s pigment is currently nearly obsolete.
These chemical properties make lithopone stable under many conditions, yet certain environmental factors, such as UV exposure, can lead to photodarkening.
Lithopone is manufactured through a precipitation process. Solutions of barium sulfide and zinc sulfate are combined, forming a double precipitate of BaSO&#; and ZnS. This precipitate is then calcined or heated to remove impurities and improve opacity. Finally, the material is quenched in water to prevent oxidation and ground to a fine powder for use in paints and coatings.
The resulting pigment offers superior hiding power and a smooth, fine texture. Historical improvements, such as doping with cobalt during the calcination process, have enhanced lithopone&#;s lightfastness and utility in artistic and industrial applications.
One of lithopone&#;s most intriguing characteristics is its historical tendency to photodarken when exposed to sunlight, a phenomenon that earned it a negative reputation in the late 19th century. This darkening occurs as zinc sulfide (ZnS) undergoes chemical reduction, forming metallic zinc that manifests as a grayish cast. Notably, this reaction reverses in the absence of light, allowing the pigment to regain its original white state. This challenge, extensively documented by researchers like W. J. O&#;Brien, highlighted the pigment&#;s sensitivity to UV exposure and initially limited its use in outdoor and durable applications.
Lithopone&#;s stigma was addressed in the 20th century as new stabilization methods emerged. Techniques such as cobalt doping and adding surface coatings, including silica or alumina layers, significantly enhanced the pigment&#;s photostability. These innovations and advanced production methods improved lithopone&#;s resistance to environmental factors.
Artists and conservators have recognized lithopone&#;s inertness and compatibility with mediums as key strengths. These make it valuable for interior applications and certain artistic uses. For more details on the historical challenges of photodarkening and the technological breakthroughs that resolved them, see the section titled &#;The Challenge of Photodarkening in Lithopone.&#;
These developments underscore lithopone&#;s enduring relevance as an artistic and industrial material, enabling its continued adoption despite its early challenges.
Lithopone&#;s adoption in the fine arts can be traced to its high opacity and economic advantages. Lithopone enabled artists to achieve vibrant highlights and subtle gradations alongside other white pigments, such as zinc oxide and titanium dioxide. Its durability has also made it a preferred choice for underpainting layers.
Art conservators frequently encounter lithopone in early 20th-century works. Studies, such as those on Van Gogh&#;s paintings, reveal its application in both ground and paint layers. Conservation research, including micro-mapping and spectroscopy, has been pivotal in identifying lithopone in historical artworks, offering insights into artists&#; materials and techniques.
Lithopone occupies a unique place in the history of art and materials science. Its development marked a shift away from toxic and less stable white pigments, providing artists with safer and more versatile alternatives. Due to its historical relevance, intriguing properties, and applications in fine art, lithopone remains a subject of interest for contemporary artists and conservators.
Understalithopone&#;spone&#;s chemical properties, historical use, and artistic potential deepen our appreciation of the complex interplay between science and art. As we continue to study and preserve historical works, lithopone is a testament to innovation in materials that have shaped artistic expression for over a century.
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.[1]
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Lithopone was discovered in the s by DuPont. It was manufactured by Krebs Pigments and Chemical Company and other companies.[2] The material came in different "seals", which varied in the content of zinc sulfide. Gold seal and Bronze seals contain 40-50% zinc sulfide, offering more hiding power and strength.[3] Although its popularity peaked around , approximately 223,352 tons were produced in . It is mainly used in paints, putty, and in plastics.[1]
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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.
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Lithopone is produced by coprecipitation of barium sulfate and zinc sulfide. Most commonly coprecipitation is effected by combining equimolar amounts of zinc sulfate and barium sulfide:
This route affords a product that is 29.4 wt % ZnS and 70.6 wt % BaSO4. Variations exist, for example, more ZnS-rich materials are produced when zinc chloride is added to the mixture of zinc sulfate and barium sulfide.[1]
Barium sulfide is produced by carbothermic reduction of barium sulfate. Zinc sulfate is obtained from a variety of zinc products, often waste, by treatment with sulfuric acid.
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Lithopone is rather nontoxic, due to the insolubility of its components. It has been used in medicine as a radiocontrast agent. Lithopone is allowed to be in contact with foodstuffs in the US and Europe.[1]
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