Oil paint consists of pigments and drying oil, such as safflower oil, linseed oil and walnut oil. Oil paints were first used in Afghanistan between the 5th and 9th century. It spread to Europe where, during the Renaissance period, it eclipsed the use of tempera paints. Unlike watercolor, oil paints dry slowly. In fact, it takes six months for an oil painting to be dry enough to be varnished and completed. In professional circles, an oil painting is not considered completely dry until it is at least 60 years old.
why do trees have leaves