Zinc Oxide for Paint Manufacture
13 November 2019
Zinc oxide (more commonly known as zinc white or Chinese white) is one of the principal white pigments developed in the 18th century. However, zinc oxide for paint manufacture apparently was not seriously considered until after the 1850s.
As one of the three white pigments (lead, titanium, and zinc), it has been used extensively for artistic and decorative paints. The most common application of the pure pigment has been in watercolors, sold under the name Chinese white, but is found often in mixtures with other pigments in oil and acrylic paints.
Zinc oxide paints tend to retain their original whiteness during aging, not only in watercolor but in oil paint as well. Compared with other white pigments ground with oil, zinc oxide for paint often exhibits the least tendency to become yellow.
Zinc oxide for paint has a tendency 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 reactivity of zinc oxide is affected by the particle size and morphology, with smaller particles being more reactive. When it comes to linseed oil, the production 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 it is used in small amounts. Zinc oxide for paint has a tendency 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.
In view of these recent findings, it is recommended not to use zinc oxide in the ground or underlayers of an oil painting and caution its use in all oil paint.
Read More: Zinc Oxide is in your Paint
Zinc oxide is compatible with all inorganic pigments. It is stable toward light in the sense that it doesn’t discolor. However, owing to its photochemical reactivity, zinc oxide for paint will affect the fading of various organic pigments. It will accelerate the light fading process of artists' paint that contain organic pigments, such as madder lake, alizarin lake, and Prussian blue.