In the Renaissance, oil painting developed as an evolution of tempera painting, the dominant form of painting for previous centuries.
Tempera paint is made from egg (or egg yolk) mixed with pigment and diluted with water. While incredibly lasting, Tempera has many drawbacks. It is very absorbent and has a porous surface which is easily stained. Its matte appearance does not show a large range of dark and rich values. When applied to a surface it dries almost immediately, preventing the blending of colors. And, it dries to a hard brittle surface that is not flexible, so therefore must be painted on stiff solid wood panels. Painting large works required joining multiple panels together that were very heavy and difficult to transport.
During the Renaissance, painters started applying oil over tempera paintings to protect the porous surfaces. The addition of this top coat created a shinier surface with darker and richer effects that offered more depth and atmosphere. The effect was so positive that painters started to experiment with oils, eventually leading to the creation of oil paints.
Oil paint is a paste made from pigment mixed with a drying oil, which when exposed to air, dries to form a flexible solid film. Historically, the drying oils used were Linseed (Flaxseed), Walnut and later Poppy. Further experimentation with oil paint lead to additives to control drying times, texture, and other effects.
One of the chief advantages of oil paints is the flexible film, allowing painters to use lightweight flexible stretched canvas. Linen was traditionally the fabric used to make canvas (made from the same plant who’s seeds are pressed to make Linseed oil). Stretched canvas became preferable to wood panels which were: hard to make, warped easily, and were heavy to transport.
As a result oil painting became the dominant painting art medium we know today.