Method of painting using pigments dispersed in oil. It is not known how oil painting was first developed, but in Western Europe there are indications of its use from at least the 12th century AD, and it was widely used from the Renaissance. . . . Egg tempera was the main paint medium of the Middle Ages before the advent of oil paint. The use of drying oils as a varnish for paintings was described by the medical writerAetius in the 6th century AD, but the earliest reference to mixing oil with pigment to make paint was not until the 12th century, in the manual De diversis artibus (c. 1110–40) by Theophilus. . . . In the northern countries, particularly the Netherlands, the transparency of oil paint was fully exploited from the outset, and a technique was developed in which layers of glazes were built up from a detailed underdrawing, like sheets of coloured glass. . . . The tempera tradition was, however, well established in southern Europe, thus the introduction of oil paint was a gradual process, with many painters continuing to work in egg and animal size during the 15th century.