Oil paint was certainly developed for ornamental or useful purpose in the High Middle Ages, although latest study indicates it was famous in the far east centuries earlier. Surfaces like shield - both those used in tournament and those hang as embellishment - were more durable when tinted in oil-based medium than when painted in the customary tempera paints.
Nearly all source, in general Vasari, ascribed northern European watercolorist of the 15th century, and Jan van Eyck in particular, with the "discovery" of painting with oil medium on wood panel, however Theophilus basically give instruction for oil-base painting in his treatise. Early Netherlandish work of art in the 15th century was however the first to create oil the usual painting, pursued by the rest of Northern Europe, and after that Italy. The popularity of oil stretch through Italy as of the North, starting in Venice in the late 15th century. By 1540 the earlier method for painting on board, tempera had become all but vanished, although Italians persistent to use fresco for barrier paintings, which was more harder in Northern climates.