Zinc White and the Influence of Paint Composition for Stability in Oil Based Media

Abstract

Zinc oxide is a prevalent pigment in twentieth century oil based paints. Its reactivity with fatty acids has consequences for paint film properties and stability. Resulting zinc carboxylates are implicated in a variety of deterioration phenomena affecting late nineteenth and twentieth century paintings. Naturally aged artists' oil paints and reference paint film draw downs are investigated using scanning electron microscopy, and conventional attenuated total reflectance and synchrotron transmission Fourier transform infrared spectroscopy. This study reports results for soybean oil paints and Naples yellow hue pigment mixtures with zinc oxide in addition to previously reported findings for linseed and safflower oil based paints involving zinc oxide alone and in combination with lead and titanium whites. A solvent model examining interactions between zinc oxide and stearic acid or aluminium stearate supports observations made in paint films. The significance of aluminium stearate as a stearic acid source in paint formulations is corroborated and is more significant than oil type or pigment combination for formation of high concentrations and more pronounced separation of saturated C16 and C18 chain zinc carboxylates.