The drying oil is a vegetable oil, often made by crushing nuts or seeds. For paints, linseed oil is most commonly used, but poppy, sunflower, safflower, soya bean and walnut oils can also been used. The advantage of the slow-drying quality of oil paint is that an artist can develop a painting gradually, making changes or corrections if necessary.
Oil paints blend well with each other, making subtle variations of colour possible as well as more easily creating details of light and shadow. They can also be diluted with turpentine or other thinning agents. A heavily diluted layer dries relatively quickly, being tack-free in a few days. Thicker layers, containing more oil, take longer. Oil paint continues to dry, getting harder with age over many decades. Pigments and extenders will also affect the rate of drying, so different colours may dry at different speeds.