Zinc Oxide Pigment
Zinc oxide, more commonly known as zinc white, is a synthetic white pigment with good hiding power, nontoxic, permanent, and usable in most mediums.
Zinc oxide is one of the principal white pigments developed in the 18th century but became popular in art only until after the 1850s. It was more commonly known as zinc white or Chinese white.
|Common Names:||English: zinc oxide, zinc white|
French: oxyde de zinc, blanc de zinc
German: Zinkoxid, Zinkweiss
Italian: oxido di zinco, bianco di zinco
Russian: цинковые белина
Spanish: oxido de cinc, blanco de cinc
|Alternate Names:||Chinese white, calamine, philosopher's wool, Chinese white, flowers of zinc|
Origin and History
Zinc oxide, more commonly known in the art world as zinc white, is one of the three white pigments—lead, titanium, and zinc—used extensively for artistic and decorative paints. Although known since ancient times, zinc white was not seriously considered an artist's pigment until after the 1850s. The most comprehensive application of the pure pigment has been in watercolors, sold under the name Chinese white, but it is often found in mixtures with other pigments in oil and acrylic paints.
Zinc compounds, predominantly in processed and unprocessed forms, have found varied applications throughout the annals of history, ranging from medicinal ointments to industrial uses. This article delves into the chronological development and utilization of these compounds. Historical records and archeological findings suggest that ancient civilizations utilized zinc compounds as fundamental constituents in paints and medicinal salves. Particularly, zinc oxide emerges as a consistent ingredient across multiple cultures.
The ancient Indian medical text, the Charaka Samhita, dated to approximately 500 BC, documents the use of pushpanjan, presumed to be zinc oxide, as a topical salve for ocular conditions and open wounds. Prominent Greek physicians such as Dioscorides and Galen cited the application of zinc oxide ointments in their respective medical treatises. The Roman Empire, circa 200 BC, was instrumental in the large-scale production of brass, an alloy synthesized from zinc and copper. Documented Roman metallurgical processes involve reacting copper with zinc oxide. In this method, zinc ore is subjected to heating in a shaft furnace, resulting in the liberation of metallic zinc vapor, which subsequently condenses into zinc oxide. Between the 12th and 16th centuries, India witnessed the recognition and production of zinc and zinc oxide using a nascent form of the direct synthesis process. By the 17th century, the locus of zinc manufacturing transitioned to China.
In 1743, the city of Bristol, UK, became the site for Europe's inaugural zinc smelting facility. By 1834, zinc white, a derivative of zinc oxide, gained prominence as a pigment in oil paintings. Despite initial challenges in compatibility, advancements in the synthesis of ZnO ensured its widespread adoption. By the mid-19th century, many European manufacturers produced zinc white paints on a significant scale due to its advantageous properties over lead-based alternatives.
In the recent past, the rubber industry emerged as a major consumer of zinc oxide, employing it primarily for its anti-corrosive properties. The 1970s marked a phase where ZnO, especially of the quality yielded by the "French Process", became an integral filler component in photocopying paper. However, subsequent technological advancements saw titanium supplanting this application.
Zinc oxide is widely available today, manufactured by numerous companies. The manufacturing process of zinc oxide is designated in commerce as the "indirect" or "French process" zinc oxide made from the metal and the "direct" or "American process," which is zinc oxide made from the ore and, hence, traditionally somewhat less pure. The terms nodular and acicular are used to describe the particle shapes.
Permanence and Compatibility
Zinc oxide paints tend to retain their original whiteness during aging, not only in watercolor but also in oil paint. Compared with other white pigments ground with oil, zinc oxide often exhibits the slightest tendency to yellow. The pigment tends to react with fatty acids present in drying oil, leading to the formation of zinc soaps. A soap is a metal salt of an organic acid. The particle size and morphology affect the reactivity of zinc oxide, with smaller particles being more reactive. In the case of linseed oil, the formation of zinc soaps from zinc oxide tends to harden the paint film. A 28-year study completed in 2007 by Mecklenburg and Tumosa of the Smithsonian Institution shows that zinc oxide can cause brittleness and delamination of oil paint film even when zinc oxide is used in small amounts. Zinc oxide tends to catalyze the formation of hydrogen peroxide when irradiated by near-ultraviolet light. This reaction and the formation of zinc soaps can cause chalking and embrittlement of oil paint films. Given these recent findings, we do not recommend using zinc white in the ground or underlayers of an oil painting and caution against its use in all oil paint.
Zinc white is compatible with all inorganic pigments. It is stable toward light in the sense that it does not discolor. However, owing to its photochemical reactivity, zinc oxide will affect the fading of various organic pigments. Zinc white will accelerate the light fading process of artists' paint that contain organic pigments, such as madder lake, alizarin lake, and Prussian Blue.
Oil Absorption and Grinding
Zinc oxide absorbs a moderate amount of oil. The oil absorption ratio varies considerably, at least from 20-25%, depending on the particle size and shape. Specific manufacturing procedures make it possible to produce pigment grades that demand less oil, 14-15% oil in paste.
Zinc oxide is not considered hazardous, but care should be used in handling the dry powder pigment to avoid inhaling the dust.
Rublev Colours Pigment: Zinc Oxide Pigment
|Pigment Type:||Synthetic Inorganic|
|Colour Index:||Pigment White 4 (77947)|
|Chemical Name:||Zinc(II) Oxide|
|ASTM Lightfastness Rating|
|Refractive Index:||ε=2.02, ω=2.00|
|Processing Time||Usually ships the next business day.|
|Pigment Type||Inorganic, Synthetic|