Lithopone: White Pigment with a Stigma

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.

The Origins and History of Lithopone

Lithopone was developed in the 1850s 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 (BaSO₄) 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.

Composition and Chemical Properties

Lithopone’s composition is a carefully engineered mixture of BaSO₄ 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 1874 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 1920s by introducing small amounts of cobalt salts before calcination.

While lithopone and anatase titanium white gained traction between the 1920s and 1950s, 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.

Table: Lithopone Identifiers and Properties

Lithopone Identifiers and Properties

Category	Details
Common Names	Enamel White, Pigment White 5, Becton White, Zincolith
Chemical Formula	BaSO₄·ZnS
CAS Number	1345-05-7
EC Number	215-715-5
Density	Approx. 4.36 g/mL
Melting Point	ZnS: > 1,180°C; BaSO₄: > 1,350°C
Solubility	Insoluble in water
Appearance	White powder
Odor	Odorless
GHS Pictogram
Hazard Statements	H302, H332
Precautionary Statements	P261, P264, P270, P271, P301+P312, P304+P312, P304+P340, P312, P330, P501
NFPA 704 (Fire Diamond)	Data not included

These chemical properties make lithopone stable under many conditions, yet certain environmental factors, such as UV exposure, can lead to photodarkening.

The Production Process

Lithopone is manufactured through a precipitation process. Solutions of barium sulfide and zinc sulfate are combined, forming a double precipitate of BaSO₄ 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.

Properties and Stability in Art

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.

Applications in Fine Art Painting

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.

Bibliography

O’Brien, W. J. “A Study of Lithopone.” Cornell University. Comprehensive exploration of lithopone’s chemistry, properties, and applications, focusing on its historical development and photodarkening behavior.
Link to PDF

Goshron, J. H. and Black, C. K. “A Study of Lithopone Darkening,” Industrial & Engineering Chemistry 1929 21 (4), 348-349. DOI: 10.1021/ie50232a021.
Link to PDF

Comelli, Daniela, et al. “On the Discovery of an Unusual Luminescent Pigment in Van Gogh’s Painting.” Journal of Heritage Science. This article highlights lithopone’s use in Van Gogh’s artworks, emphasizing its identification through spectroscopy.
Read the article

Capogrosso, Valentina, et al. “An Integrated Approach Based on Micro-Mapping Techniques for Detection of Impurities in Zn-Based White Pigments.” Journal of Analytical Atomic Spectrometry. Discusses advanced analytical methods for identifying lithopone and its impurities.
Read the article

The Challenge of Photodarkening in Lithopone

Lithopone darkens when ZnS is reduced under UV exposure, producing metallic zinc, which alters its optical properties. This reversible reaction occurs primarily in environments with fluctuating light exposure, complicating its use in outdoor or durable applications. The need to stabilize lithopone has led to research into chemical modifications and protective strategies.

Stabilization Techniques for Lithopone

Cobalt Doping

Cobalt doping is a well-documented method to enhance the photostability of lithopone. By incorporating cobalt ions (Co²⁺) into the zinc sulfide (ZnS) lattice, researchers have effectively reduced the pigment’s susceptibility to photoreduction. This doping process stabilizes electron-hole recombination dynamics within the ZnS structure, thereby minimizing the formation of metallic zinc—a byproduct responsible for darkening under UV light. A study published in Langmuir (2016) identified cobalt doping as a significant advancement for ZnS nanoparticles, which are integral to lithopone. Beyond photostability, this method has improved water resistance and overall pigment durability.

Surface Coatings and Additives

Surface coatings, such as silica or alumina layers, provide an additional layer of stabilization for lithopone. These coatings act as physical barriers, shielding the pigment from exposure to light, moisture, and reactive environmental agents. The coatings reduce the photodarkening rate by preventing direct interaction between ZnS and external reactive species. Aluminum hydroxide has also emerged as a valuable additive, forming insoluble protective complexes on the pigment’s surface. These protective mechanisms enhance lithopone’s resilience and extend its functional lifespan in various applications.

Matrix Embedding

Embedding lithopone in polymer or inorganic matrices has proven to be an effective strategy for stabilizing the pigment. Such matrices restrict the mobility of zinc and sulfur ions, mitigating the risk of photoreactive processes that contribute to pigment degradation. Research published in the Journal of Coatings Technology highlights hybrid formulations where lithopone is co-doped with stabilizing agents and embedded in polymer systems. This method improves stability and enhances the pigment’s compatibility with industrial and artistic applications requiring high durability.

Chemcations

Chemical treatments, such as adding phosphates or carbonates during lithopone synthesis, inhibit darkening by neutralizing reactive intermediates. These compounds act as scavengers for free radicals and reduce the chances of reduction-oxidation cycling in ZnS【18†source】.

References

Nicola, M., Garino, C., Mittman, S., Priola, E., & Palin, L. “Increased NIR Photoluminescence of Egyptian Blue via Matrix Effect Optimization.” Materials Chemistry, 2024.
Read the article.

Weide, P., Schulz, K., Kaluza, S., Rohe, M., & Beranek, R. “Controlling the Photocorrosion of Zinc Sulfide Nanoparticles in Water by Doping with Chloride and Cobalt Ions.” Langmuir, 2016.
Read the article.

Puthran, D., & Patil, D. “Usage of Heavy Metal-Free Compounds in Surface Coatings.” Journal of Coatings Technology and Research, 2023.
Read the article.