Did Jan van Eyck really invent oil painting?

No. Jan van Eyck did not invent oil paint, although the Renaissance writer Giorgio Vasari said he did and the myth stuck. The oldest known oil paintings are Buddhist murals painted around 650 AD in caves in Afghanistan's Bamiyan Valley, and European monks were writing about oil-based paint by about 1125. What van Eyck and his Flemish contemporaries did was turn oil into the normal medium for serious pictures, and show what it could do: astonishing detail and deep, glowing colour.

The secret was patience in layers. Oil paint is pigment suspended in an oil such as linseed, and it does not dry by evaporating like water but by slowly reacting with oxygen. Egg tempera, the old panel medium, dried fast and made corrections hard. With oil, a painter could rework, blend colours wet into wet, and lay down thin, translucent glazes one over another. Light passes through those glazes, bounces off a white ground underneath, and comes back out, which is why van Eyck's jewels, fabrics and faces seem lit from within.

Van Eyck knew how good he was. He signed his work with the motto ALS ICH KAN, 'As I can', a pun on his name, and on the Arnolfini Portrait he wrote 'Jan van Eyck was here 1434'. Within a century, the technique had swept through Europe, and by 1540 tempera panels were all but extinct.