Um... while oil painting was not a popular artistic medium until appx 15th century, it was hardly considered founded then, as it was know to be used in as medium in home décor. However - The oldest known oil paintings date from 650 AD, found in 2008 in caves in Afghanistan's Bamiyan Valley, "using walnut and poppy seed oils." after that, Mediterranean cultures used vegetable oils for many things, it is not proven they used it in their artworks.... most commonly referenced used oils are 'drying oils' such as Walnut, Poppy, Pine nut, Castor, hempseed AND linseed oils.
RE: van Eyck specifically (and other artists afterwards:(snipped from
https://en.wikipedia.org/wiki/Oil_paint)
The Early Netherlandish painting of the 15th century saw the rise of the panel painting purely in oils, or oil painting, or works combining tempera and oil painting, and by the 16th century easel painting in pure oils had become the norm, using much the same techniques and materials found today. The claim by Vasari that Jan van Eyck "invented" oil painting is not correct but has cast a long shadow, but van Eyck's use of oil paint achieved novel results in terms of precise detail and mixing colours wet-on-wet with a skill hardly equalled since. Van Eyck’s mixture may have consisted of piled glass, calcined bones, and mineral pigments boiled in linseed oil until they reached a viscous state—or he may have simply used sun-thickened oils (slightly oxidized by Sun exposure). He left no written documentation.
The Flemish-trained or influenced Antonello da Messina, who Vasari wrongly credited with the introduction of oil paint to Italy,[4] does seem to have improved the formula by adding litharge, or lead (II) oxide. The new mixture had a honey-like consistency and better drying properties (drying evenly without cracking). This mixture was known as oglio cotto—"cooked oil." Leonardo da Vinci later improved these techniques by cooking the mixture at a very low temperature and adding 5 to 10% beeswax, which prevented darkening of the paint. Giorgione, Titian, and Tintoretto each may have altered this recipe for their own purposes.
The use of any cooked oils or Litharge (sugar of Lead) darkens an oil painting rapidly. None of the old Masters whose work survives used these in their paintings. Both ingredients became popular in the 19th century. Since that time, experiments to improve paint and coatings have been conducted with other oils. Modern oil paints are created from bladderpod, ironweed, calendula and sandmat, plants used to increase the resistance or to reduce the drying time.
What Types of Oils are Used in Oil Paint? (per
http://www.visual-arts-cork.com/oil-painting.htm#oil)
The most popular type of oil used in painting is linseed oil because (unlike other vegetable oils like olive or canola oil) it dries by oxidation. Linseed oil is not the only drying (or siccative) oil: safflower, poppy seed, or walnut oil may also be used, depending on the sheen, drying time and other effects required by the painter. However, linseed oil tends to dry faster and, in the process, forms a more flexible paint film that can be reworked more easily. Note also, that pigments do not dry at the same speed: charcoal black oil paint, for instance, tends to be slower to dry while red/yellow ochre hardens much faster.
more equally interesting information on Oil Painting/Pigments, etc -
https://www.britannica.com/art/oil-painting
by Derexbrown » Thu Jan 19, 2017 7:41 am 
