Painters had mixed pigment with oil long before the fifteenth century, but in Flanders in the 1400s, Jan van Eyck and his contemporaries refined it into something new. Paint bound in linseed oil, rather than egg tempera, stayed workable for days. A painter could blend on the canvas, build up thin layers one over another, and come back to a passage later to change it. Tempera had never allowed that. Six hundred years on, no medium has replaced it.
The Chemistry of Permanence
Oil paint does not dry the way water evaporates. It hardens slowly as the oil takes in oxygen from the air, and the result is a flexible, tough film. A painting on linen, primed with lead white, built up "fat over lean" (each layer a little oilier than the one beneath) and finished with varnish, can stay sound for centuries. We know because many have. Van Eyck's Arnolfini Portrait was painted in 1434 and can still be seen in London today.
That durability is a large part of why collectors who hope a painting will outlast them, and pass to their children and grandchildren, still choose oil on canvas. Acrylic and watercolour have their own strengths, but neither has five centuries of evidence behind it.
The Range That No Other Medium Matches
Oil can go on as a glaze so thin you barely see it, or as impasto thick enough to cast its own small shadows. It can flow, or sit on the canvas like butter. It can be scraped back, painted over, wiped off with a rag or glazed with a colour from the other side of the spectrum. Through all of it, it still answers to the painter's hand.
This is why painters who start in oils seldom leave. Over the years each one settles into a palette, a preferred drying time, even the smell of a particular studio. Oil also pushes back: rush it and the layers turn muddy or crack. That resistance is part of what makes the finished work good.
Why Contemporary Painters Keep Returning
The twentieth century brought acrylics, alkyds and, later, digital tools, and each has its painters. Even so, oil, turpentine and linen are still at the centre of a great many studios today.
Part of the reason is that oil asks for patience and technical knowledge, and serious painters tend to welcome that. Another is that an oil painting rewards looking. From across a room you see the composition; at a metre, the drawing; close up, every brushmark and the order in which they were laid. A screen flattens all of that, which is why an original oil painting has to be seen in the room to be seen at all.