MITRA Forum Question Details

​We recently had a very similar query come in regarding this topic (one that dates back to the time of Jan van Eyck in fact). We recommend reading our response on the other thread which you can find here and let us know if you have any additional questions.

Probably we should avoid the phrase “forced drying” in this context, and reserve that for paints that either dry by evaporation, or in the case of oil paint, the addition of catalytic metal driers. As you know, oil paints dry by oxidation. In this scenario, the light, and consequent heat, may slightly speed up the oxidation rate (due to the fact that higher temperatures will increase reaction rates) as well as the action of UV light accelerating aging. If taken to extremes, the speed of reactions will be increased more at the surface of the paint than below the surface. This does occur naturally in oil paint films because of the greater availability of oxygen at the surface, but, in theory, you are only exacerbating this with prolonged exposure to heat and unfiltered light.

The effect in reality is probably minimal beyond perhaps jump starting oxidation reactions. I do think that most of the impact of sun is to bleaching out some of the components that contribute to yellowing. Prolonged light exposure should be avoided for obvious reasons including the Increasing fading of sensitive pigments.