Lithopone Pigment

Rublev Colours Lithopone is an organically coated white pigment based on a co‑precipitated zinc sulfide/barium sulfate compound. The zinc sulfide content is 30% by weight, whereas, on a molecular basis, lithopone consists of the two components at a ratio of 1:1. It is a transparent white almost equal to zinc oxide in whiteness. It holds a medium position in density between lead white and zinc white.

History

The inception and evolution of lithopone can be traced back through various industries and diverse applications. Revered for its robust hiding power, this white pigment, also called sulfide of zinc white, has been an invaluable asset to industries requiring a durable and reliable white pigment. Lithopone was an economical and functional solution as an alternative to lead carbonate, which is prone to change, and zinc oxide, known for its brittleness.

Historically, the first mentions of zinc sulfide being utilized as a pigment were approximately sixty years before the everyday use of lithopone. Originally, it was thought to be appropriate for coloring rubber. In England, a patent was granted for this process. Two decades after this, the focus shifted to zinc sulfide as a suitable pigment for paint. The year 1874 witnessed the patenting of a manufacturing process for a novel white pigment composed of zinc sulfide and barium sulfate. Dubbed Charlton white or Orr’s white enamel, this began a new era for white pigments.

Composition

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.

Permanence and Stability

From a stability standpoint, lithopone, a fusion of zinc sulfide and artificially precipitated barite, is non-toxic and exhibits resilience to mild lyes and acids. However, it is incompatible with colors containing copper. Despite its strong covering power in oil, lithopone’s drying capabilities are notably limited, posing potential issues for artists. Notably, early experimentation with lithopone-based grounds instead of zinc white resulted in undesirable darkening, although this blackness receded upon drying. This unpredictable behavior has sparked debate among scientific communities, emphasizing the need for further exploration and understanding of this pigment.

With its storied history and distinct properties, lithopone remains a subject of historical significance and contemporary relevance. While its applications and popularity have evolved, its role in the annals of pigment history is indisputable.

For a detailed explanation of the terms in the table above, please visit Composition and Permanence.