Did you know that oils do not dry by evaporation, but by light curing? This means that if you leave an oil painting in a dark room, it will stay wet for a long long time. This can be used to your advantage if you get interrupted while painting and want it to stay workable longer. It’s not a good idea to delay the drying for too long though. A few days is fine, but longer than that and the paint might have a tendency to yellow. However, if you are in a hurry to dry an oil painting, putting it under bright light both day and night really helps speed things up. But using a hot hair dryer to try to speed up oil paint drying is a completely useless exercise.