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Why do alkyds have a tendency to yellow?
By Rick Watson
Ask Your ProPartner columnist
Alkyd paints tend to yellow more as the paint film ages. Time is not the only culprit in case of the yellowing paint. Other factors come into play. The actual yellowing phenomenon is caused by the resin used in the alkyd/oil-based paint. All alkyd/oil-based paints use some type of resin as a major component and, upon drying; these resins may become slightly yellow. This color change results from the chemical composition of the resin itself and the additives needed to obtain an acceptable drying rate. Different chemical compositions of these resins result in different degrees of yellowing. In addition to certain resins contributing to yellowing, another variable that can come into play is the presence of ammonia.
Ammonia
Most do not realize that the ammonia in latex paints can contribute to the yellowing of an alkyd coating. Ammonia also may be emitted from household cleaners. This reaction to ammonia is most commonly recognized in certain areas of kitchens and bathrooms. Areas most commonly cleaned with ammonia containing detergents will exhibit the highest degree of yellowing.
Light
Another factor that can contribute to yellowing is the presence or absence of light. This phenomenon occurs because electrons in the paint reach a more excited state brought on by exposure to certain wavelengths of ultraviolet light. This changes the paint film’s behavior. The degree of yellowing may continue to increase or decrease with changing exposure to light.
Drying additives
A final factor in yellowing is the use of paint additives called driers. Oil-based paint formulas require some type of additive, or drier, in order to ensure that the paint film dries properly. Depending on the resins and driers used, these factors may also contribute to the yellowing phenomenon.
What's the answer?
One solution is to consider using a high-quality latex paint. While some latex paints result in a slightly softer film that an alkyd, they will perform quite well in most areas traditionally painted with an alkyd and will, thus, eliminate most possibilities of yellowing.
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