Zinc Oxide is In Your Paint

28 June 2018


Paints are complex mixtures of substances (pigments, resins/binders, solvents and additives). They are applied on walls (indoor), facades (outdoor), vehicles and furniture, among other purposes. Depending on the surface type, e.g. concrete, bricks, stone, wood, metal or glass, they are developed to meet particular requirements: decorative appearance; protection against radiation, humidity/water, microorganisms; fire protection and thermal insulation. There are water- and oil-based paints, which can have additional functionalities depending on the necessities of the consumer. One of the most important ingredients is Zinc Oxide. It Used primarily in primers and exterior paints, Zinc Oxide provides mildew resistance, corrosion inhibition and stain blocking support.

Zinc Oxide is the principal white pigments commonly known as zinc white or Chinese white. Zinc oxide or more commonly known in the art world as zinc white is one of the three white pigments -- lead, titanium and zinc. It is stable toward light in the sense that it does not discolor. Zinc Oxide paints tend to retain their original whiteness during aging, not only in watercolor but to a great extent in oil paint as well. Compared with other white pigments ground with oil, zinc oxide often exhibits the least 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 reactivity of zinc oxide is affected by the particle size and morphology, 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 study 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 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 paints films. In view of these recent findings, we do not recommend the use zinc white in the ground or underlayers of an oil painting and caution its use in all oil paint.

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. Certain manufacturing procedures make it possible to produce pigment grades that demand less oil, 14-15% oil in paste. There are some benefits of Zinc Oxide, such as UV absorbing pigment, toughens film, can improves water resistance, neutralizes harmful acids, coatings formulated with zinc oxide Indonesia provides provide improved biocidal, color retention and durability properties.