Oil paint is a richly textured medium. The slow-drying paint gives the artist time to manipulate and continuously work it until the desired effect is achieved.
Oils are creamy paints that you can work with for hours, without the stress that it will dry before you achieve your desired effect on the canvas. A painter can go back to the canvas and over paint on wet or dry oil paint.
When working on an oil painting, it is important to keep it from being damaged. Wet oil paint can be rubbed off and would have to be repainted.
Oil paint can be mixed with turpentine, linseed oil and mineral spirits to make it flow in a thinner layer on to the canvas. These materials can effect the speed at which the oil paint dries on the top surface of the painting.
Oil paintings will appear to be dry within a few days. The top layer will only have dried enough to allow you to touch it without paint residue clinging to your fingers.
An oil painting can take several months to dry completely as each color and medium used has it's own individual drying time. The top layers feel dry to the touch when in reality the painting is not completely dry all the way through the layers.