How Oil Paints Work: Art Fundamentals

A technical revolution in the history of art

Detail of ‘Portrait of a Carthusian’ (1446) by Petrus Christus. Oil on wood. The Metropolitan Museum of Art, New York. Images source The Met (open access)

The invention of oil painting was an enormous turning point in the story of Western art. It enabled artists to represent the world around them with a level of detail never seen before. And because of the ability of oil paints to be layered in semi-transparent glazes, works of art became luminous in their depth and resonance of colour.

The important thing to remember about oil painting is that it really refers to the “medium” of the paint rather than to any special aspect of the pigments used to make the colours.

The “medium” is the liquid substance that holds the pigment and dilutes it. Before they are mixed with a medium, a paint pigment is usually in the form of a finely ground powder. Traditional sources of pigment were various: for instance, the colour known as ultramarine (a vivid blue) came from the ground-up rock lapis lazuli, whereas the colour vermilion (brilliant red) was originally made from the powdered mineral cinnabar.

Cinnabar mineral and the powered form of vermilion. Images sources Wikimedia Commons & Wikimedia Commons

More unusually, the colour Indian yellow was once produced by collecting the urine of cattle that had been fed only mango leaves. In more recent times, natural pigments have given way to synthetically derived colours, but the principle remains the same.

From egg to oil as the carrier medium

Before the adoption of oil as the medium, artists used other liquids to play the role. Tempera was popular, where an emulsion of egg yolk and water was used to make the pigment usable as paint. Tempera was capable of producing very fine paintings, often onto wood, but had the drawback of drying quickly and with a matte, opaque finish.

When oil painting arrived, artists made immediate use of its slow drying nature, which meant they could work more patiently over the finer details of their work. They also utilised the fact that oil paint can be thinned and then applied in semi-transparent layers, otherwise known as “glazes”.

With glazes, paint can be built up with one colour overlaying another. When light penetrates the paint layers, it reflects back the full spectrum of layered paint, giving a more resonant and luminous feel.

Image by author.

For a long time, it was thought that oil painting was invented in Northern Europe in the 15th century, by the painter Jan van Eyck in particular. But in fact oil painting had been in use in Middle Eastern countries like Afghanistan since at least 650AD, and in Europe since the Middle Ages.

Still, it was Jan van Eyck and his contemporaries from the Netherlands who, in the 1400s, took oil painting to new heights. Take a painting like Portrait of a Carthusian by Petrus Christus, painted in 1446. Christus was based in Bruges in present-day Belgium, and was active between 1444 and 1476 — the year he is thought to have died.

Portrait of a Carthusian (1446) by Petrus Christus. Oil on wood. The Metropolitan Museum of Art, New York. Images source The Met (open access)

The extraordinary naturalistic detail of paintings like Portrait of a Carthusian was a profound innovation in European art.

To underline the realistic possibilities of his oil paints, Christus added a telling detail to his portrait. Look towards the bottom edge of the painting and notice a small fly perched on what appears to be the picture frame. This lower ledge, along with the inscription, is all painted invention.

From pigs’ bladders to tubes

Early artists mixed their own pigments with heat-bodied (gently-heated) linseed oil, derived from crushed flax seeds, sometimes adding beeswax to prevent the paint from darkening as it dried. They worked through a patient process of grinding the powdered pigments into the oil to achieve a smooth, honey-like consistency.

Monte Pincio, Rome (c.1840) by Jean-Baptiste-Camille Corot. Oil on canvas. Art Institute Chicago. Image source Art Institute Chicago (open access)

Up until the mid-1800s artists would typically transport their mixed paint in a pig’s bladder. Such was the case with the French painter Jean-Baptiste-Camille Corot, who adopted an effective practice of travelling and painting outdoors during the summer months, making studies and sketches directly from nature.

Yet this was not an easy situation. Bladders didn’t travel well and frequently burst open. And to get at the paint, Corot would have to prick the bladder with a pin, after which the hole was difficult to completely plug.

In 1841, the portrait painter John Goffe Rand invented the metallic paint tube. Soon enough, manufacturers of oil paints began to offer paint in tubes with screw caps to preserve the paint.

This simple development allowed artists to more easily carry their paints with them, opening up the possibilities of painting on location for many more artists. The artist Pierre-Auguste Renoir is quoted as saying: “Without paint in tubes there would have been… nothing of what the journalists were later to call Impressionists.”

Moreover, with paint in a more accessible form, artists began to enjoy a greater flexibility of brush marks, from thick impasto (thickly textured paint) to finer details. This dexterity of oil paint has left a permanent mark on the course of Western painting.

Vincent van Gogh’s thick brushstroke “impasto” technique. Wheat Field with Cypresses (1889). Oil on canvas. Metropolitan Museum of Art, New York. Image source Wikimedia Commons

Artists as wide-ranging as Vincent van Gogh and Willem de Kooning, utilising the versatility of modern tube-based paints, learned to use paint expressionistically. Their paintings forged an imprint of the very moment of creation, and with it, an indelible record of the artist’s response to the world.

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