Chapter XCVIII

If I knew that my portrait was still at Antwerp, I would have it kept back for the case to be opened, so that one could see that it had not been hurt by so long a time spent in a case without being exposed to the air, and that, as often happens to colours freshly put on, it has not turned rather yellow, thereby losing all its first effect. The remedy, if this has happened, is to expose it repeatedly to the sun, the rays of which absorb the superfluity of oil which causes this change; and if at any time it still turns brown, it must be exposed afresh to the sun. Warmth is the only remedy for this serious mischief.

_Rubens._

EFFECTS OF TIME ON PAINTING