We have noticed that our white paints based on long·oil soyabean alkyd resins become yellow in darkened rooms. What could be the cause?
Soyabean alkyds generally show less tendency to yellow than linseed oil alkyds, because of their lower content of linolenic acid. Since you refer to white paints, the cause could be a small percentage of zinc oxide. You could also try to find out whether the location where the paint is used is very damp and whether there is ammonia present since this would almost certainly cause yellowing in the dark.
The most important countermeasure for painted surfaces is to admit UV radiation - even if it is only sunlight. This will not only suppress the reactions which accompany the process of yellowing in the resin, but will bleach the paint film.
Yellowing of soyabean alkyds in the dark
Blog, Updated at: 5:17 PM
