Sometimes science lags so far behind art that painters are left to fall back on proto-sciences like alchemy. The results are all too often disaster for art. With the advance in science brought by the Enlightenment and the rise of colourmen, the eighteenth century should have seen improving quality and standards in oil painting. Although that may be true in some respects, some of the most conscientious painters discovered how to make their art self-destruct through alchemy.

The problem at the heart of this is that it took around six centuries for anyone to start to comprehend how oil paint works. The development of oil painting techniques was almost entirely the result of careful observation and hit-or-miss experimentation. It wasn’t really understood scientifically until the twentieth century how drying oils binding pigment particles together in a paint layer changed from creamy liquid to a robust solid. The process is a combination of oxidation and polymerisation, but can so easily change into saponification, resulting in runny soap rather than the long-living paint layer we all hope for.

What often lured painters to stray from tried and tested materials and techniques was the mystique surrounding the Old Masters of the Renaissance, Rubens, van Dyck, and most of all Rembrandt.

Sir Joshua Reynolds (1723–1792), founding president of the Royal Academy in London, was a notable victim. He had a conventional training in oil painting with Thomas Hudson (1701-1779), a successful portrait painter who used traditional and conservative methods with roots going back to the late 1600s. This used layers, starting with dead colouring, the laying in of shadows and lights, then blending in transitions of shading and colour wet-on-wet. Highlights were then brought out, and shadows glazed, to produce a series of thin layers, and a smooth, finished paint surface.

Reynolds’ early stages are shown well in this abandoned portrait of Mrs Robinson (c 1784), where most of the paint layer is sufficiently thin as to allow the texture of the canvas to show through.

His portrait of Anne Seymour Damer (née Conway) (1773) shows this technique working well, with painterly highlights, and textures in the fabrics. That of flesh has aged well, with limited fine cracking visible.

Reynolds aspired to the greatness of the Masters, and in his quest to achieve that, he experimented, particularly after he visited Italy in 1749-52. Most of his canvases were supplied stretched and primed by colourmen, but Reynolds appears to have customised his paint composition very considerably, if he didn’t have it made to his own specifications.

Seeing that the works of Masters, such as Rembrandt, had passages with quite thick applications of paint, Reynolds also applied his paint thickly in appropriate passages. In order to make the paint viscous enough for that, he took to adding mediums which he felt resembled those used by the Masters. He seldom scraped back paint in order to correct or change his paintings, but applied more paint over the top of as many as ten previous layers, some of them quite viscous and thick.

Reynolds himself admitted that his Infant Hercules Strangling Serpents in his Cradle (1788) had “ten pictures under it, some better, some worse.”

His records of ‘experiments’ with paint are not given in sufficient detail to reproduce any of his materials, but contain references to the use of copaiba balsam (a controversial oleo-resin thickener which can inhibit drying), wax (which he was convinced was the secret of success of the Masters), and bitumen (which inhibits drying). His drying oils were linseed, walnut, and poppy seed, with the latter two mainly used for lighter-coloured paints. They were often heat-treated to pre-polymerise and thicken them.

But his greatest downfall, as far as the longevity of his paintings is concerned, was his excessive use of resins, including mastic, pine, and copal, as well as the oleo-resin copaiba balsam. Contemporaries recorded that some of his portraits cracked before they had even left the studio.

Reynolds also experimented with the most dangerous medium of all: Megilp. Known by a variety of similar names, he is the first British artist known to have referred to its use. Megilp is made by heating a drying oil with a lead drier (usually litharge), then adding substantial amounts of resin until it produces a thick paint of buttery consistency. Variants using different kinds of ‘black oil’ were even more likely to compromise the longevity and structural integrity of paintings. Reynolds seems to have been addicted to them.

His portrait of Lady Sunderland (1786) has survived rather better than many of his paintings.

But a more careful look at its background shows where paint, presumably diluted with turpentine to aid its rapid application, has run, although other parts of the same brushstroke still show the marks of the brush, indicating that the paint had also been thickened prior to dilution.

His Cupid Untying the Zone of Venus (1788) has catastrophic cracking indicating that surface layers of paint have detached from lower layers. In parts, those cracks have become filled with lighter paint which has risen up from a lower layer, which was drying more slowly than the more superficial layers. This detail also shows the wide variation in thickness of the paint layer: some passages are thin enough to allow the texture of the canvas to show through, while others are so thick that layers have separated.

Similar loss of structural integrity has afflicted his Infant Hercules Strangling Serpents in his Cradle (1788), in its thickly-painted passages.

Other parts of that painting appear to be in need of extensive conservation work to restore details which have become largely unintelligible because of problems in the paint layer.

Sadly, Reynolds was not the first, and by no means the last, painter to compromise their oil paintings from their desire to emulate the Masters. There were also many more who were tempted to use Megilp and its variants, in the forlorn hope that it would improve their paintings.

Unlike Reynolds, JMW Turner didn’t experiment with unconventional materials and techniques in an attempt to recreate the appearance of Old Masters, but this resulted from his remarkable explorations of the combination of colour contrasts and texture. His extensive use of paint based on drying oil and lead white brought rapid changes during drying, and commonly serious problems with cracking.

The techniques, their success and failure are 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-established ‘fat over lean’ rule. Here they have clearly not done so, and that has resulted in patchy areas of cracking.

Some areas are worse affected, with apparent wrinkling probably resulting from the slumping of impasto, and undried paint exuding. Here this is most probably the result of Turner’s use 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.

My third example comes from French Impressionism and Post-Impressionism, in the unusual practice of what was termed peinture à l’essence by Edgar Degas and others.

Tubed oil paints, particularly certain colours, can be a bit oily, and it seems that Degas and others experimented with reducing the amount of oil in their paints. Squeezing paint out of the tube onto blotting paper or rag and removing excess oil should not cause any problems, but peinture à l’essence took that to an extreme, in blotting out as much oil as possible, and restoring viscosity and flow by adding turpentine.

Degas’ Dancer in her Dressing Room (c 1879) is one of his experimental paintings which uses both pastels and peinture à l’essence applied to canvas. The detail view below shows how thinly he applied his paint to the ground, although it’s impossible to judge from that how well it’s adhering.

Oil paint has been so successful and its paint layers so robust because the pigment is sealed in its protective layer of polymerised oil. Pastels adhere far more tenuously, with precious little to bind them to the ground. Removing the drying oil and adding essentially unbound pigment will inevitably result in a very fragile painting.

Tragically, as scientists were coming to understand better how oil paint works, during the twentieth century, it again became popular to deliberately break long-trusted rules. As a result, many avant garde paintings of recent times are slowly self-destructing. Imagine paying a small fortune for a painting which falls apart as its value should be increasing.

Reference

Gent A (2015) Reynolds, Paint and Painting: a Technical Analysis, in Joshua Reynolds, Experiments in Paint, eds. L Davis & M Hallett, The Wallace Collection & Paul Holberton. ISBN 978 0 9007 8575 7.