Since the decline of egg tempera as the preferred medium for easel paintings in the Renaissance, oil paints have dominated those used by professional painters. This is due to their longevity and versatility. When appropriate techniques are used, oil paintings readily survive over five hundred years, and are the closest we have come yet to a permanent medium.
At the heart of every oil painting is a robust paint layer consisting of pigment particles bound in polymerised and oxidised drying oil, traditionally derived from a vegetable oil. The most common binder is linseed oil, extracted from the seed of the common flax plant, and there are alternatives obtained from safflower, poppyseed and walnut, and beyond Europe in perilla, soya bean and tung.
It has been claimed that poppyseed oil was used as a binder in Afghanistan in about 650 CE, but its subsequent use is doubtful. The use of other drying oils became established in northern European art by about 1250; although those were known in and around the Mediterranean since ancient times, their ability to oxidise and form a paint layer wasn’t exploited there until much later.
The other key ingredients for these drying oils to be used widely in painting are suitable diluents and solvents: this required the distillation of ‘spirits’, which didn’t start until the twelfth century, when mineral spirits, turpentine and lavender oil started to become available.
The earliest examples of substantial oil paintings are altar frontals and other church decorations in Tingelstad and other locations in Norway, and date from around 1275. The frontal shown above is a modern reconstruction which demonstrates their sophistication. Over the following century, purification and treatment of drying oils improved, and various treatments were discovered to accelerate the process of drying, which could otherwise take may weeks to reach the stage at which a layer could be overpainted.
There is evidence of the early use of pre-polymerisation by sunlight and heat to initiate the drying process, and the admixture of siccatives to catalyse the chemical reactions involved in drying. Pre-polymerisation also has the advantage that it thickens the oil, and when pigment is ground in, results in more viscous paints which are easier to apply with brushes.
The first great masterpieces painted in oils started to appear in the early fifteenth century across the ‘low countries’ from northern France through Belgium and the Netherlands. Workshop assistants prepared the paints for each day’s work, by grinding pigment with the oil until the paint consisted of fine pigment particles dispersed evenly in the oil binder, using a type of pestle conventionally known as a muller, normally on a flat, smooth block. The muller and block were later made of glass, but in early workshops are likely to have been fashioned from polished hard stone.
Some started to add resin thickeners to alter the viscosity of the oil paint. Although there was some trade in more exotic resins from southern Europe and elsewhere, the main resin found in early oil painting in northern Europe is pine resin, which was melted into the oil before mulling in pigment. Resins also have the advantage that they adjust the optical properties of the paint layer, and were discovered to enhance the ‘look’ of paintings as a result.
Oil paintings were generally constructed in layers, on a wooden support with a ground of chalk. Some layers used opaque paint made by adding lead white pigment or filler, others were more transparent colour. Four or more layers were not uncommon, and gave the painter the ability to build up colour and texture in a highly controlled way.
By the middle of the 1400s, oil painting had been used in northern European art for over 200 years, and in the workshops of the van Eycks and their contemporaries it had flourished in ways simply not possible with other media such as egg tempera and fresco. But in Italy, with the southern Renaissance well under way, drying oils were still not used as a primary painting medium. Over the next half century, Italian painters didn’t just catch up with developments in the north, but – in some respects at least – took the lead in technical development.
The introduction of oils to Italy was largely the result of the paintings of Antonello da Messina (actually Antonello d’Antonio), who was probably a pupil of Niccolò Colantonio (c 1420-1460) in Naples, and was in contact again with northern European techniques when he was in Venice in the 1470s. Colantonio seems to have learned oil painting from Flemish artists who were brought to the court of Alfonso V of Aragon, who was King of Naples from 1442-1458, and an enthusiast for northern European paintings.
Surprisingly, with Venice the trade centre that it was, early Italian painters in oils appear to have used predominantly linseed oil as their binder, and pine rather than more exotic resins, in accordance with practice in the north. As you can see, Antonello’s paint layers are very smooth in finish, do not show any brushstrokes or impasto, and generally have a minimum of only fine cracks.
As early as 1501, Giovanni Bellini and Giorgione started to use impasto, initially in fine details of fabrics, metalwork, and jewellery, where those details were applied in the upper layer of paint.
Over the next decades, such impasto passages were used by many Italian artists, and found their way to northern Europe by way of Martin van Heemskerck, who visited Rome between 1532-36.
Two Northern artists advanced the repertoire of techniques significantly. Those of Peter Paul Rubens are best seen in his oil sketches and studies, which he produced in preparation for finished works, and occasionally as paintings in their own right. He achieved great economy of effort by making as few virtuoso marks as was necessary to form each object within the painting, and often left an uneven paint surface where there was shallow impasto, brushstrokes, and occasional incised sgraffito.
For this he relied on careful control of the viscosity of his paints, and on his great and masterly skills in applying that paint.
In the five hundred or so years since drying oils had first been used to make artistic paintings, virtually no use had been made of the surface texture of the paint layer. The expected standard for oil paintings was a smooth surface finish, although some painters had (controversially) left brushmarks and other evidence of the painting’s making. It was Rembrandt who changed this, particularly in the later part of his career.
His surface textures are usually richest in passages depicting fabrics, decorated metals, and the like, but in his David and Jonathan (1642) even plain textiles bear fine brushmarks. This was well before the date usually accepted for his radical late style.
The artists’ colourman may have first appeared as a skilled assistant in a big workshop, then realised that they could make a living from supplying stretched and primed canvases, prepared oil paints, and other materials to several smaller workshops, individuals (who might be wealthy amateurs, perhaps), and eventually even to larger workshops.
It had long been known that excluding air from drying oils prevented them from drying, and someone discovered that oil paint would remain fresh when it filled a small bag, such as a pig’s bladder. By the late 1700s, artists’ colourmen throughout Europe were selling their oil paints in these bladders.
In Quadrone’s witty Every Opportunity is Good (1878), we’re given a detailed look at the painter’s paraphernalia, including several paint bladders on the low table behind the easel, and one on the floor. Although painted well after the introduction of paint tubes, bladders remained relatively cheap and popular quite late in the 1800s.
Paint bladders transformed oil painting, most of all because they made oil paint portable. No longer was the painter constrained to using oil paints in the studio, but they could take a lightweight easel, small panels or canvases, and some bladders of paint outdoors, and paint en plein air, with the landscape in front of them.
Experimentation with new techniques has sometimes caused problems in the paint layer. When innovative artists like JMW Turner broke from the traditional and empirical rules of oil painting, the results often suffered in longevity. This is shown well in one of Turner’s most famous paintings on canvas, The Fighting Temeraire tugged to her last Berth to be broken up (1839).
Turner applied high chroma paint quite thickly on top of already thick and layered paint. Although this produces breathtaking effects, as shown in this detail, it will result in problems with cracking unless those superficial layers dry more slowly than layers underneath, a phenomenon embodied in the well-known ‘fat over lean’ rule. Here they have clearly not done so, and patchy areas of cracking are the result.
Some areas are worse affected, with apparent wrinkling probably resulting from the slumping of impasto, and undried paint exuding. This is most probably the result of Turner’s use here of bitumen or asphalt, which inhibits the oxidative ‘drying’ of linseed oil, and commonly leads to problems in the paint layer. Sadly bitumen was a popular pigment in the 1800s, although its adverse effects were well known.
JMW Turner was also one of the first painters to make use of the latest pigments, including chrome yellow, which he purchased in tubes rather than bladders. It was John Goffe Rand who patented what he termed “metal rolls for paint” in 1841. At first, these were seen not so much as a means of increasing the portability of oil paints, but for their cleanliness and lack of odour.
Adoption among professional painters at the time was patchy: these new tubes were expensive, and required filling equipment which many of the existing colourmen did not see was necessary. Oil paint continued to be sold in bladders for several decades afterwards, although newer pigments offered by the larger and more innovative colourmen often only came in tubes.
Coupled with a lightweight portable easel and canvas-carrier, tubed paints made oil painting truly portable, and outdoor landscape painting became enormously popular in Europe and North America.
By the start of the twentieth century, artists like the virtuoso John Singer Sargent were able to paint quite substantial works in the confines of a small bedroom, something impossible in the past. I doubt that his work was as well-appreciated by the housekeeper.
Advances in industrial chemistry in the twentieth century have opened up new potential in oil painting. Alkyds have been added to traditional drying oils to accelerate drying even further. Rising concerns with the toxicity of solvents such as turpentine used in traditional oil painting have brought water-miscible oils, a supension of fine particles of oil paint, still with their drying oil included. Carefully packaged with a series of additives such as surfactants – detergents, as they are more commonly known – these are extremely convenient in use.
These give the illusion that, thanks to modern chemistry, oil and water do mix. Deepening understanding of oil paints among conservation experts and the array of scientists who now support them has raised a new issue in oil painting technique: the threat of soap formation in the paint layer.
The triglycerides which make up drying oils will only polymerise into a robust paint layer in the right conditions – they require oxygen, for example – and very slowly. Given different conditions, they can turn into soap, which has none of the physical properties required for a paint layer to last many centuries.
Some apparently well-constructed paint layers in oil paintings have been seen to saponify to such an extent that they drop off the ground in large sheets, resulting in total loss of the painting. In other cases, deeper saponified layers can remain liquid, and ooze from holes and cracks which open in dry surface layers.
We clearly still have much to learn about oil paint, painting with oils, and how to make paintings which will last as long as those of Rembrandt and van Eyck.