Paulus Bor (1601-1669) was born in the city of Amersfoort, to the north-east of Utrecht, and seems to have started his training locally before going to Rome, where he was one of the founders of a ‘secret’ society of Netherlandish expatriates, the Bentvueghels (‘birds of a feather’). He returned to Amersfoort to perform some decorative painting, then pursued a successful career there until his death in 1669. Apart from a Caravaggist tendency during his early career, he might seem a run-of-the-mill painter of the Golden Age.

What distinguishes Bor are his little-known portraits of women in trouble, images that dig deep into the psyche, long before the Age of Enlightenment.

The first of these is Ariadne, painted in the period 1630-35, which is reminiscent of Caravaggio, and a little mysterious. When Theseus came to Crete to kill the Minotaur, Ariadne helped him by giving him a ball of golden thread that he used to retrace his route out of the labyrinth after he had killed the Minotaur (her half-brother). Ariadne fell in love with Theseus, and the couple eloped to Naxos, where he abandoned her.

Bor’s portrait can only show Ariadne on Naxos, immediately after she has been abandoned, still clutching the thread by which she thought she had tethered Theseus, now hanging at a loose end. On the wall above her are sketches she has made of her lover. She looks deeply lost in thought and gloom. This may refer to Ovid’s imaginary letter from her to Theseus in his Heroides.

Then, in about 1635, Bor painted The Magdalen, clutching her bottle of myrrh and looking straight at the viewer. She too is troubled, and has clearly been crying.

At about the same time, he painted this Allegorical Figure, also known as an Allegory of Logic. Coiled around her right wrist is a snake, but she too looks straight at you. The reptile appears venomous, and could easily be a European adder (or viper), or even an asp of the type Cleopatra used to kill herself.

Bor’s last two portraits of women in trouble have clearer narrative bases.

The Disillusioned Medea (The Enchantress) from about 1640 appears unique among the images of the enchantress who used her magic to support Jason in his quest for the Golden Fleece. She fell in love with Jason, married him on his voyage home, and bore him two children. Ten years later, Jason divorced her for the King of Corinth’s daughter Glauce.

This was too much for Medea, who sent Glauce a poisoned wedding dress that killed her and her father horribly. She then killed her two children, and fled to Athens, where she had a child by King Aegeus. Ovid includes an imaginary letter from her to Jason in his Heroides.

Medea sits, her face flushed, resting her head on the heel of her right hand. In her left, she holds a wand made from bamboo or rattan. The wand is poised ready for use as soon as she has worked out what to do next. Behind her is a small altar, similar to Diana’s in Bor’s painting of Cydippe below, and the statue at the left is of Diana.

The last of these portraits is undated, but it has been proposed it was painted as a pendant to The Disillusioned Medea, thus in about 1640. This is also based upon two letters in Ovid’s Heroides, and his Art of Love.

Acontius was a young man from the lovely Greek island of Keos, who fell hopelessly in love with the beautiful young Cydippe. Sadly, she was of higher social standing than he was, and such a marriage was unthinkable to her family. He came up with an ingenious plan to trick her into making a commitment to him: he wrote the words I swear before Diana that I will marry only Acontius on an apple.

He then approached Cydippe when she was in the temple of Diana, and threw the inscribed apple in front of her. Her nurse picked it up, and handed it to Cydippe to read his words aloud before the altar, so binding her to the vow. She then seemingly overlooked this inadvertent commitment that she had made.

Her family had other ideas, and found her a prospective husband of appropriate status. Shortly before the couple were due to marry, Cydippe fell ill with a severe fever, and the proceedings were postponed. After she recovered, another attempt was made to marry the couple, but she again fell ill just before the ceremonies, so the wedding had to be called off yet again.

Unsure of what to do next, Cydippe’s parents consulted the oracle at Delphi, who told them the whole story. Recognising the strength of the vow that she had made, Cydippe and her parents finally accepted the match, and Acontius and Cydippe married with their blessing.

Bor’s Cydippe with Acontius’s Apple puts a different slant on the story: here, Cydippe leans on the altar, alone, the inscribed apple held up in her right hand. But she isn’t reading Acontius’ words: she has clearly already said those out aloud, and now seems to be thinking through the vow she has just made.

Bor paints the details of the altar exquisitely. Cydippe’s dress may be anachronistic, but the artist brings in the skull of a sacrificed goat and festoons of flowers.

Although Cydippe’s story is alluded to in Spenser’s Faerie Queene, appears in verse by Edward Bulwer Lytton and the artist and designer William Morris, and is told in six operas, including Hoffman’s Acontius and Cydippe, first performed in 1709, this appears to be its only significant depiction until the late eighteenth century.

Bor’s cycle of paintings of troubled women is unusual, and stands comparison with explorations of the mind in Rembrandt’s Bathsheba with King David’s Letter (1654) and Lucretia (1666), also far in advance of their time.

Painting in the Golden Age didn’t occur in isolation, but was greatly influenced by artists of Flanders and Brabant to the south, many of whom visited or migrated to the Dutch Republic. Some Dutch artists effectively exported their landscape and other skills to Italy, where there was a group of emigrés known as the Bentvueghels (meaning birds of a feather) between about 1620-1710.

From the late 1590s until well into the following century, the distinctive style of Caravaggio (1571-1610) drew followers across Europe, most of whom saw his paintings when they were training in Italy. This wave of Caravaggism spread when those painters returned to their native lands, including the states of the Dutch Republic.

Caravaggio’s style was by no means unique, and his use of chiaroscuro had been anticipated a century earlier in this wonderful nocturne by the early Netherlandish painter Geertgen tot Sint Jans, Nativity at Night, thought to be from about 1490. Chiaroscuro makes narrative sense here, and results in a scene of great tenderness and reverence, thanks to its soft transitions of tones.

Caravaggio’s third painting of Salome Receives the Head of John the Baptist was completed in about 1609-10, shortly before his death, and illustrates his style at its height.

Artemisia Gentileschi’s father was a well-known Caravaggist, and she followed suit for the early years of her career. Her painting of Judith Slaying Holofernes followed a decade later in 1620-21. Over that period, Hendrick ter Brugghen, Gerrit van Honthorst, Dirck van Baburen and Jan van Bijlert became influenced when in Italy, and returned to Utrecht, where they have become known as the Utrecht Caravaggists.

Van Honthorst’s The Soldier and the Girl from about 1621 is a good example, where the young woman is lighting her candle from a burning coal.

Van Honthorst’s dimly lit indoor scenes are associated with pleasures, often fairly sinful ones, as in his Merry Company from 1623. He shows here how directional lighting can transform appearance, turning quite ordinary or ugly faces into caricatures.

As music was breaking out of seedy dens of iniquity into mainstream culture, learning to play an instrument and playing to others became fashionable, as shown in van Honthorst’s merry Concert on a Balcony from 1624.

During the 1620s his paintings became more narrative and less Caravaggist, as seen in his Solon and Croesus from 1624. This shows the elderly Greek statesman getting a hostile reception from Croesus, with his court laughing at his responses. Included are two slaves supplicating themselves before the king, in an interesting condemnation of slavery for its time.

Some more mainstream artists also showed Caravaggist tendencies.

Rembrandt’s very early painting of The Operation from 1624-25 shows a barber-surgeon and his assistant performing surgery on the side of a man’s head, by the light of a commonplace candle on a candlestick holder.

Hendrick ter Brugghen’s religious narrative of Jacob Reproaching Laban for Giving him Leah in Place of Rachel is from the later years of Caravaggism, in 1627.

Although remarkably little is known of the paintings of Judith Leyster, she appears to have been influenced when painting in Haarlem.

Like most of her surviving paintings, A Game of Tric-Trac was made before her marriage to Jan Miense Molenaer, in this case in 1630.

Although Rembrandt’s use of chiaroscuro is best known from his later paintings, Saint Peter in Prison (The Apostle Peter Kneeling) dates from 1631.

Later interiors and genre works show the more lasting influence imported from Italy.

Long before paintings became movable objects of great value used by the rich as investments, artists and the owners of their paintings wanted to protect the paint layer that had been so carefully applied to the ground. From the early Middle Ages onwards, one popular means of doing this has been to apply some form of protective layer, a varnish.

Varnishes have been widely used not only for protection. Careful choice of their composition can enhance the appearance of a painting, through the optical properties of the varnish medium and its smooth, glossy surface. Until the late nineteenth century, the great majority of painters either applied final layers of varnish themselves, or advised their patrons and clients to do so.

Three types of varnish have come into common use:

• Drying oil and resin, in effect a resin-rich transparent and unpigmented paint layer, that usually becomes an integral part of that. Some artists have added pigment, perhaps to make a general colour adjustment. There isn’t any clear distinction between that and a final paint glaze.
• Solvent and resin, from which the solvent will evaporate, leaving a thin surface coat of resin.
• Water-based washes such as egg white, known as glair, vegetable gums like gum arabic, and animal glues.

Resins used in varnishes have rich and sometimes strange histories. Most are exudates from trees in exotic locations, and have evocative names like mastic, sandarac, colophony and dammar. They’re usually highly insoluble, either in drying medium that has to be heated to make oil-based varnishes, or in turpentine or similar organic solvents. A great many recipes have been proposed, and there’s always the lure of the perfect, and inevitably top secret, formula.

The biggest problems with varnishes are their propensity to yellow or grey with age, and their tendency to take up dirt and atmospheric contaminants. Rembrandt’s first painting of Bathsheba at her Toilet from 1643 has sadly lost much of its detail into the gloom of old varnish, which can be almost impossible to clean off when composed of drying oil and resin, without damaging the paint layer underneath.

Any work older than a few decades that has been varnished or had any form of surface treatment is unlikely to appear today with the colours the artist intended. Multiple layers of old varnish and trapped dirt give a misleading impression of what we would have seen soon after the work was completed. Painstaking work by conservation specialists can often restore old paintings to what we presume is their former glory, in full colour again.

Hieronymus Bosch’s Christ Carrying the Cross (1490-1510) is seen above before recent conservation work, and below is the result of thousands of hours of painstaking cleaning and treatment.

Another problem for the conservation specialist is a painting like Edward Poynter’s A Visit to Aesculapius from 1880. Although this is little more than a century old, the evidence from contemporary prints made from this work is that it was originally far from being so dark. Sadly it’s now almost impossible to read as a result of its near-black shadows.

A good varnish should be both colourless and transparent, but painters haven’t always respected that.

When finishing his monumental Raft of the Medusa in 1819, Théodore Géricault is thought to have applied glazes or varnish containing asphalt to give the painting a deep brown tone. Asphalt is not only completely unprotective and almost attracts dirt, but it never fully dries, and can have adverse effects on underlying paint too. It hasn’t helped that this two hundred year-old painting was rolled up and stored in a friend’s studio when it remained unsold, and was then transported to London still rolled up the following year.

Conventional wisdom says that it’s best to leave an oil painting to dry for at least six months before varnishing it. JMW Turner sometimes varnished over paint layers that were far from dry. In the case of The Opening of the Wallhalla, 1842 (1843), painted on mahogany, Ruskin reported that it had “cracked before it had been eight days in the Academy Rooms”, although this overall view shows little evidence of that damage.

Hellen and Townsend attribute this to Turner’s extensive use of Megilp, here a product sold by his colourman containing leaded drying oil and mastic varnish. Used sparingly and with great caution, such medium modifiers don’t necessarily cause serious ill-effects. But Turner has used Megilp to excess, to produce a soft impasto used in the foreground figures, in particular. This has resulted in wide and shallow drying cracks, as the surface has dried quickly and shrunk over trapped layers of liquid paint.

Varnishes do provide mechanical protection to the paint layer, but at the cost of locking out atmospheric oxygen, required for drying oils to polymerise properly in their drying process. Applied too early, varnishes can therefore greatly slow drying of underlying paint layers; the danger is that they may saponify (turn to soap) instead of drying normally.

Despite these dangers, varnishes can, when used with care by those who understand them properly, be valuable beyond simply providing a protective coat. Kirsty Whiten’s The Quing of the Now People (2015) achieves its superbly realistic effect by the skilful combination of conventional oil paint with varnish.

In the late nineteenth century, attitudes to varnishing oil paintings changed markedly, as Impressionists like Camille Pissarro started to prescribe that their works should on no account be varnished. This was to preserve the soft matte surface of the paint as applied by the artist, and became increasingly popular in the twentieth century.

For such paintings, protection can be provided by glass, when necessary. That isn’t of course an option for many extremely large oil paintings on canvas, which will probably need to be varnished and cleaned periodically well in the future, as they have in the past.

Varnishes, usually of the third type containing vegetable gums or animal glues, have also been used extensively on paint layers other than oils.

These are reported in Samuel Palmer’s Tintern Abbey at Sunset, above, and Dante Gabriel Rossetti’s Lucrezia Borgia, below. Gum or glue varnishes can have impressive optical effects when used carefully on watercolours.

Unfortunately, their tendency to yellow can also cause colour shifts. William Blake liked to apply glue varnish to his watercolours and perhaps to his glue tempera paintings as well. In the case of his Penance of Jane Shore in St Paul’s Church from about 1793, this has resulted in a generalised yellow shift and loss of chroma.

Other artists appear to have been more successful: Henry Ossawa Tanner apparently applied varnish to this tempera painting of The Destruction of Sodom and Gomorrah almost a century ago, and it doesn’t appear to have suffered any adverse consequences, yet.

Varnishing has become such an accepted process that major exhibitions have incorporated ‘varnishing days’, although what happens on those occasions can be quite different. In Turner’s day at the Royal Academy in London, Varnishing Day was an occasion for artists to make any last-minute changes, and Turner himself seems to have turned up armed with paint and brushes and continued to work on his paintings.

Varnishing Day in the Paris Salon was completely different, attended normally by the artists’ colourmen, who applied a coat of varnish to the paintings for which they were responsible. The artists themselves don’t seem to have been involved, unless they chose to apply the varnish in person.

We’re remarkably good at perceiving different surface textures, but find it harder to imagine them in two-dimensional images. While the overwhelming majority of paintings, at least until the twentieth century, consist of a paint layer on a flat ground, there’s nothing that requires the surface of the paint layer to be flat and smooth. But if all you look at are images of paintings, you generally won’t see their surface texture, where the artist has applied and shaped paint in thick layers of impasto, or incised into some of the layer in sgraffito. This article looks in detail at four examples where surface texture in the paint layer is important.

Arnold Böcklin’s unusual painting of Sirens from 1875 was made in tempera on canvas, with the ground and paint layers thin enough to let the texture of the canvas weave show through. This image was fortuitously taken with lighting that allows the texture to show.

Another famous tempera painting wasn’t painted on a textured ground, but is one of the earlier paintings to feature impasto as a technique.

The Wilton Diptych was painted on two small panels of oak wood in the final years of the fourteenth century. That wood was first assembled into the panels, then carved down from a thickness of about 2.5 cm (1 inch) to form an integral frame with a recessed painting surface. A smooth gesso ground was then laid on the wood before the gilded areas were laid onto it using thin sheets of gold leaf, and patterned using a range of punches.

Details of jewels and similar objects such as the white hart brooches were raised using thicker areas of lead white paint, to give the impression of enamelling. Coupled with mordant gilding, they mimic the three-dimensional form of jewels and act as point reflectors of light, sparkling as if they really were gems in the paint layer, as shown in the details above and below.

The finest strokes of paint seen here are less than 0.5 mm (1/50th of an inch) across.

From those early days of modern painting until the decline of ‘academic’ painting in the late nineteenth century, patrons, Salon juries and critics expected paint surfaces to be smooth and flat. But there were rebels.

Many of Rembrandt’s paintings from before 1650 have fairly conventional ‘finished’ surfaces, his monumental Night Watch being a good example. By about 1660, though, many of his paintings had quite rough surfaces that significantly alter their optical properties.

One of the best examples of Rembrandt’s use of texture in the paint layer is The Jewish Bride from about 1667, just a couple of years before his death. This is among his works studied by the Rembrandt Research Project.

In this detail, highlights on the sleeve and jewellery have been applied roughly, although it’s still a matter for speculation as to exactly how he achieved that. Lower down, on the red dress of the bride, the duller top layer of paint has been scraped through to reveal lighter lower layers. The end result is a painting that creates its visual effects as much by its surface textures, as by form or colour.

One of Rembrandt’s secrets that have been sought by so many since lies in how he was able to exploit surface texture in his paint. That is the ‘secret recipe’ which Maroger, Redelius, and others claimed to have discovered. Systematic analyses of Rembrandt’s paint layers by White at the National Gallery in London and the Research Project soundly rebutted the ‘secrets’ claimed. In the main, Rembrandt used linseed oil as his binder, occasionally using walnut oil as well, and just once poppy seed oil.

In some passages the oil had been thickened by heat treatment, but this was by no means widespread. Traces of pine resin found in some samples may have been introduced during retouching, and don’t appear to be a feature of Rembrandt’s impasto work; neither is there any evidence that he added wax to his oil paint to give it body, as some had asserted.

As you might expect, JMW Turner was another such rebel.

For example, in his Seapiece with Fishing Boats off a Wooden Pier, a Gale Coming In, possibly from as early as 1801, Turner made extensive use of sgraffito, made using a knife, brush handle, or even his fingernails for all we know.

Later that century, Vincent van Gogh developed a more radical approach, in his initial version of Wheat Field with Cypresses from 1889, the year before his death.

It’s possible that he completed this painting in a single sitting, as this seems to have been intended as an oil sketch for a more finished version which he painted later that summer.

The detail above shows the tops of the wheat towards the lower left of the field, in the foreground. Over his initial thin layers of paint, van Gogh laid thick gestural strokes of highly chromatic paint, orientating those strokes according to the object they show. In the golden yellow of the wheat there are blues and greens, mostly showing through from his underpainting, with superimposed impasto of pale straw, ochre, and pale greens.

This detail, taken from the edge of the wheatfield at the lower right corner of the painting, shows three distinct areas of brushwork: the diagonal strokes forming the standing wheat, swirling loops to form the grasses and weeds below, and shorter marks forming a more random pattern for the heads of the wheat in the upper section.

At the centre of the canvas, from where this detail is taken, impasto blue and white have mixed with the green and yellow of the fields below. This shows that much of the painting was painted wet on wet, either in the same session or on consecutive days. Some of the darker green at the right may have been painted later, onto paint that had by then become touch dry.

An X-ray image of the whole painting shows in white those passages likely to contain the most lead white, and some other pigments which are most radio-opaque. This also reveals the pattern of brushstrokes well.

With the introduction of acrylic paints in the latter half of the twentieth century, painters have been able to apply even heavier impasto, and some have used this to paint what are in effect reliefs.

This is why so many paintings have to be seen in the flesh, up close, and in the right light for their full appreciation.