The yellowing of oil paint is affected by the pigment, vehicle, drier, and environment. It has been reported that the presence of zinc oxide in paints decreased the yellowing tendency of oil paint, which is why this pigment is used by most artist oil paint manufacturers in white and light-colored oil paints despite its tendency to cause paint embrittlement. Studies also show that titanium dioxide causes yellowing instead of bleaching when exposed to light. One author also showed that lead white and lithopone in white films accelerated yellowing. Another study carried out by L. Simpson studied which types of titanium dioxide pigment affected the rate of yellowing. The results showed that yellowing increased in the following order: coated rutile pigment, non-coated rutile pigment, and last anatase titanium dioxide pigment.
The effect of driers on the yellowing of linseed oil-based paints was studied by several authors. Decreasing drying time, caused by increasing the amount of drier, results in greater yellowing. Cobalt or manganese naphthenate driers caused less yellowing than their corresponding oleates and resinates. Fortunately, naphthenate driers are the most common driers used by artists today. Another author, L. Rakoff, studied the effect of drier composition on the yellowing of linseed oil-based paint films. Films containing cobalt or lead driers yellowed with similar rates and to a greater extent than films with manganese driers. The effect of film thickness on yellowing is greater with cobalt driers, less with lead driers, and not significant with manganese driers. With both single-metal driers and multiple drier complexes, thicker paint films yellowed more rapidly than thinner paint films.
Heat and the absence of light are responsible for the yellowing of oil paint films. According to Werthan and his colleagues, high temperature and humidity accelerate the yellowing process. They also showed that yellowing is influenced by light wavelength. Yellowing is less in red wavelengths of light, followed by green and blue wavelengths.
What factors influence the yellowing of oil paint?
The yellowing of oil paint is affected by the pigment, vehicle, drier, and environment, including temperature, humidity, and light wavelength.
How does the presence of zinc oxide affect oil paint yellowing?
Zinc oxide decreases the yellowing tendency of oil paint, which is why it is commonly used in white and light-colored oil paints despite its tendency to cause embrittlement.
Which pigments are associated with increased yellowing in oil paintings?
Titanium dioxide, particularly when uncoated rutile pigment, non-coated rutile pigment, or anatase titanium dioxide, accelerates yellowing. Lead white and lithopone in white films also contribute to yellowing.
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