Although oil is probably one of the most familiar media used, few truly know or understand what is involved in creating an oil painting. It is a process which became popular in the 15th Century, although it had started several centuries earlier. Many different types of oils have been used such as linseed, poppyseed, walnut and safflower oil. Each oil has different properties and drying times, thus producing different results. The artist will usually begin by sketching the image onto a canvas. The pigmented oil is then applied in layers. Careful application is needed for each layer to prevent cracking or peeling. Various tools can be used to transfer the oils to the painting surface. Although paint brushes are used traditionally, other methods include palette knives or even rags. Since oil paint remains wet longer than many other types of artists' materials, it allows the artist to makes changes to his work much more easily. Since oil paint dries by oxidation, it usually takes about two weeks to dry to the touch, however, it is not completely dry enough to apply vanish for another six months to a year.