What is a defining feature of the drying process for oil paints?

The defining feature of the drying process for oil paints is that they can take several days to dry. This characteristic is primarily due to the chemical reaction that occurs as the oils oxidize and polymerize when exposed to air. Unlike water-based paints, which dry through evaporation and can set quickly, oil paints require a longer time to form a solid film as they slowly lose moisture. The drying time can be influenced by various factors such as the thickness of the application, the type of oil used, and environmental conditions like humidity and temperature. This slower drying time allows artists greater flexibility for blending and layering techniques while working on their pieces.

The other options describe processes that do not accurately reflect the behavior of oil paints. While some paints dry quickly or instantly, oil paints are known for their slower drying times, making them distinctive in the realm of painting mediums. Additionally, oil paints do not typically require heating to enhance the drying process; instead, artists might use mediums or additives formulated to speed up drying when necessary.