A pair of organ works that scholars believe were written by a teenage Johann Sebastian Bach were premiered in Leipzig this week and added to the composer’s official catalog.

© Jens Schlueter/Agence France-Presse, via Bach Archive/AFP Via Getty Image

The judge sided with families of students who had argued that the displays infringed on their religious freedom.

© Meridith Kohut for The New York Times

Gov. Greg Abbott said the state could now take steps to shut down the Council on American-Islamic Relations. The group said the declaration had no basis in fact or law.

© Carter Johnston for The New York Times

Many of the greatest paintings succeed in part because they use optical effects in their paint layer. This takes advantage of the fact that thinner layers of paint aren’t completely opaque, so allow some light to pass through them. In watercolours, transparent paints are often referred to as transparent watercolour, while those that are opaque are known as gouache or body colour. In oils, different pigments result in degrees of opacity, expressed as their covering power.

This cross-section of the paint layer from Honoré Daumier’s The Strongman (c 1865) demonstrates how many oil paintings consist of a series of layers, with several pigments present through their depth. Generally, the most opaque are applied first, and on top of those come a series of thinner transparent layers or glazes. Together these allow complex combinations of reflection and refraction of light, generating optical effects.

Layered oil painting technique is best seen in paintings that have been abandoned before completion.

The British portrait painter Sir Joshua Reynolds received a conventional training in traditional and conservative methods with roots dating back to the late 1600s. He painted in 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 of oil paint, and a smooth, finished paint surface.

Those early stages are shown well in this abandoned portrait of Mrs Robinson from about 1784, where most of the paint layer is sufficiently thin as to allow the texture of the canvas to show through. When used with ‘lean’ paint, this dried quickly and complies with the longstanding edict of applying ‘fat’ over ‘lean’, so that the lowest layers dry first.

Richard Parkes Bonington’s unfinished Venice: The Piazza San Marco (1827-28) shows signs that it might have been among his best. Its buildings have a golden glow from the setting sun, but those colours would undoubtedly have been enhanced by rich glazes had he lived long enough to complete it.

Occasionally the paint layer develops problems that demonstrate the effects of glazes.

In Abraham Bloemaert’s The Adoration of the Magi from 1624, the cloak of the Virgin Mary appears to use two different blues, with its lower passages painted in the duller hue of indigo, which has faded. The dullest areas are those that had the thinnest ultramarine glazes applied, much of which have now abraded away during subsequent cleaning of the painting. The unprotected indigo has therefore suffered sufficient exposure to fade, as well as losing those rich glazes.

JMW Turner’s Approach to Venice (1844) was painted with very thin transparent glazes over thick white impasto, creating a distinctive flickering effect in its highlights.

Despite the artist’s efforts to get the white impasto to dry more quickly, the glazes dried first, and cracked as they became stressed over the white that was still wet. This hasn’t been helped by the later conservation process of lining, which places an additional layer on the back of the canvas to help the support do its job.

Although a wide range of pigments have been used successfully in glazes, some were developed specifically for the purpose. From the fifteenth century onwards, verdigris pigment was mixed with natural resins for use in glazes. This produces a different pigment from regular verdigris, as the copper combines with the resin acids to form what is known as copper resinate.

A popular technique among many masters to produce an intense green was to paint an underlayer using verdigris, over which several glazing layers of copper resinate were then applied. Although generally reliable and stable, verdigris and copper resinates have a tendency to turn brown on the surface. Thankfully this affects relatively few paintings.

Tintoretto used copper resinate glazes in several of his paintings, most notably the rich, varied, and often lush vegetation in his Saint George and the Dragon from about 1555.

Studies at the National Gallery, London, have found copper resinate in three of the four paintings in Paolo Veronese’s series The Allegory of Love. In the third of these, Respect (c 1575), the pigment was found in the man’s intense green cloak, and the duller gold-brown brocade patterning on the wall behind his hand (detail below). The surface of that wall has superficial brown discoloration of the paint layer.

One of the last major uses of copper resinate is in Arnold Böcklin’s Triton and Nereid from 1874. This is reported as being painted in tempera, but copper resinate glaze appears to have been used to develop the intense green patterns on the sea monster in the foreground. This is consistent with Böcklin adhering to traditional techniques despite working in the late nineteenth century.

During that century, painting slowly in multiple layers with glazes progressively fell from favour. By the end, many oil painters had adopted techniques in which much or all of a painting was made at once, known as direct, alla prima or au premier coup.

Many great literary works are compilations of shorter tales, set in a framing story. Among the best known are One Thousand and One Nights and Sanskrit epics including Mahabharata. Among the most enduring in post-classical Europe is Boccaccio’s Decameron, whose stories have also proved popular with painters. Over the next couple of months I’m going to summarise those that have been well depicted in this new series, and show those paintings.

Despite the number of scholars who have researched Giovanni Boccaccio’s life over the last seven hundred years, much of it remains vague. He was either born in Florence, or perhaps near the village of Certaldo to the south-west of the city. His father worked for the Bardi bank, but he is thought to have been illegitimate and his mother hasn’t been identified.

We do know that he was born on 16 June 1313, and while still a child his father married a woman from a rich family, then moved to Naples. At the time, that was a major cultural centre, and as a young man Boccaccio immersed himself in that. His father expected him to become a banker, and Giovanni started work as an apprentice in his father’s bank in the city.

Boccaccio had no interest in banking though, and persuaded his father to let him study canon (ecclesiastical) law at the city’s university. When he was in his twenties, his father introduced him to the Neapolitan court and cultural circles around Robert the Wise, King of Naples. Among Boccaccio’s most important influences at this time was the scholar Paolo da Perugia, who had amassed much information about classical myths. Boccaccio became a scholar, particularly of the classical world, a writer rather than an ecclesiastical lawyer, and his future started to crystallise when he wrote his first poetry.

His early works became sources for Chaucer’s Troilus and Criseyde (Troilus and Cressida), and the Knight’s Tale.

Boccaccio left Naples in 1341, as tensions were growing between its king and the city-state of Florence, and returned to live mainly in Florence, although he also spent time in Ravenna. He developed great admiration for the work of Dante Alighieri, who had died in Ravenna twenty years earlier, and the great poet Francesco Petrarca (Petrarch) (1304-1374), whom he regarded as his teacher.

Giorgio Vasari is now more famous for his biographies of the important painters of the Renaissance and earlier, but was also an accomplished artist himself. His tribute to some of the greatest writers of the period is Six Tuscan Poets from 1544. From left to right, I believe these to be Dante Alighieri, Francesco Petrarca (Petrarch), Guido Cavalcanti, Giovanni Boccaccio, Cino da Pistoia, and Guittone d’Arezzo.

William Bell Scott’s undated painting of Boccaccio’s Visit to Dante’s Daughter shows the writer paying indirect homage to his illustrious predecessor. Boccaccio wrote the first biography of Dante, at about the same time he was writing the Decameron.

During the 1340s Boccaccio appears to have been developing the idea of a book in which seven characters take it in turns to tell stories. When the Black Death struck Florence in 1348, killing Boccaccio’s stepmother, this provided him with its framing story. He was already building his collection of tales to form the bulk of the book, and it’s thought he started its writing shortly after the Black Death. What is more doubtful is whether Boccaccio was living in Florence when the epidemic struck. However, as it raged through the whole of Tuscany in that year, hardly sparing a village, it’s most unlikely that he didn’t observe its effects somewhere, perhaps in Ravenna.

In 1349, Boccaccio’s father died, leaving Giovanni as the head of the household. In spite of that, he pressed on and had largely completed the first version in 1352. He revised it in 1370-71, and ever since it has been widely read, translated into all major languages, and its stories have inspired many works of art.

Egide Charles Gustave Wappers painted Boccaccio Reading from the Decameron to Queen Johanna of Naples in 1849. Queen Joanna I of Naples (1328-1382) had a reputation that was more than controversial, but Boccaccio was a supporter, and wrote a complementary account in his collection of biographies of famous women, De Mulieribus Claris (On Famous Women).

This miniature by the Master of 1482 and Follower conflates Boccaccio, the Black Death in Florence, and the framing story of the Decameron: Giovanni Boccaccio and Florentines who have Fled from the Plague was painted in about 1485 on vellum, in what must have been one of its first illustrated editions.

The Decameron opens with a description of the horrific conditions and events that overwhelmed Florence when the Black Death struck, then takes us to a group of seven young women who are sheltering in one of its great churches. They decide to leave the city rather than waiting amid its rising pile of corpses, to spend some time in the country nearby. They take some servants and three young men to accompany them there.

Once settled in an abandoned mansion, the ten decide that one of the means they will use to pass their self-imposed exile is to tell one another stories. Over the next two weeks, each tells one story on every weekday, delivering a total of one hundred, hence the title of the book.

Raffaello Sorbi show the group of ten during one of the story-telling sessions in The Decameron from 1876, with the city of Florence in the distance.

Salvatore Postiglione’s undated, ornate and almost illustrative Scene of the Narration of the Decameron is unusual for omitting one of the seven young women, but links visually to their other musical and craft activities.

Relatively few of the hundred tales in the Decameron have been committed to paint. Some are little more than brief fables, or what used to be known as shaggy dog stories. Others are more lengthy novellas with intricate twisting plots. But many have been painted from the Renaissance until well into the twentieth century, and were particularly popular with the Pre-Raphaelites.

The tale of Griselda has cropped up in folk stories across Europe before it was told as the final tale (Day 10, Story 10) of the Decameron. It was then taken up by Chaucer in the Clerk’s Tale, and by Charles Perrault. Francesco Pesellino painted it in this Scene from the Life of the Griseldis from around 1450.

One of the most significant series of paintings of the Decameron is Sandro Botticelli’s Story of Nastagio Degli Onesti, of which this is the first. Boccaccio includes this horrific tale as the eighth story on Day 5, shown by Botticelli in four panels that were commissioned as a wedding gift for a couple whose marriage was partly arranged by Lorenzo the Magnificent (Lorenzo de’ Medici), ruler of the Florentine Republic in the late fifteenth century, and Botticelli’s patron.

One of the earliest and greatest examples of Pre-Raphaelite painting is John Everett Millais’ Isabella (Lorenzo and Isabella) from 1848-49. When exhibited at the Royal Academy in 1849, it was accompanied by lines from John Keats’ poem Isabella or the Pot of Basil, referring to the story of the ill-fated love of Lisabetta for Lorenzo, the fifth told on Day 4.

Later in the nineteenth century, Marie Spartali Stillman painted The Enchanted Garden of Messer Ansaldo (1889), showing a scene from the fifth story of Day Ten. This was also painted by John William Waterhouse in 1916-17.

Perhaps the most popular of all the stories in the Decameron with visual artists has been the romance of Cymon and Iphigenia, here shown in Frederic, Lord Leighton’s luscious and languid painting from 1884.

I hope that you will join me in looking at many more wonderful paintings exploring Boccaccio’s stories from the Decameron in the coming weeks.

What unrevealed details have made Trump so intent on preventing further disclosure?

She has shown herself more willing than most to put aside her own ego for the greater good.

Professional artists have long used brushes to apply paint in their finished work, and many used hand-held sticks of pigment only when sketching in preparation. Charcoal has been widely used, with metal wire in silverpoint an alternative. In the sixteenth century, large deposits of graphite were discovered in Cumbria, England, following which graphite sticks and sheathed pencils became enormously popular among both amateurs and professionals.

Although it’s impossible to make any clear distinction between drawing and painting, those stick-based media are simple compared with oil paints, and seldom used in works comparable in their aims or sophistication to professional oil or watercolour painting.

The first changes in practice resulted from the French Revolution and Napoleonic Wars at the turn of the eighteenth to nineteenth centuries. Graphite was a strategic product, as it was used as a refractory in the manufacture of cannonballs, and supplies to France all but dried up. In 1795 Nicolas-Jacques Conté used a mixture of clay, graphite and other pigments to form sticks similar to pastels but significantly harder, referred to as hard pastels or Conté crayons.

As with charcoal and graphite sticks and pencils, Conté crayons were first used for preparatory sketching. By the middle of the nineteenth century, artists like Jean-François Millet extended their use into pastel paintings including his enchanting and mysterious The Cat at the Window from about 1857-58. Because of their hardness, Conté crayons were more amenable to sharpening, so could make finer lines and a richer range of marks.

Millet’s most famous painting in pastel and Conté crayon is this 1865-66 version of The Sower, a motif that was to recur in the hands of others for the rest of the century, and works perfectly in what were still relatively unconventional media.

Conté crayons, like pencil, charcoal and pastels, rely on mechanical adhesion rather than any polymerising binder. Specialised papers with roughened surfaces were marketed to improve their adhesion, but they share similar problems of longevity. However, at a time when mark-making was becoming popular, the wide range of effects available from sticks of pigment was an attraction: not only could the artist place bold strokes of colour over stumped-smooth areas, but they could also paint on textured grounds to great effect.

One of the masters of the Conté crayon was the Divisionist Georges Seurat, who used textured papers to give his paintings or drawings a highly granular appearance, as if they were photographs.

The rise of industrial chemistry and manufacturing industries in the nineteenth century brought other new painting sticks. Wax crayons effectively functioned as a low-temperature encaustic, and became popular in schools. They were adopted for resist techniques in watercolours, notably by John Singer Sargent, and some artists started using them in combination with other media.

Félicien Rops’ painting of a Hamadryad from about 1885 uses a wide range of media, drawn from those already popular among the illustrators of the day.

Another enthusiast for mixed stick media was Odilon Redon, for instance in his painting of Sîta from about 1893.

Although the mainstream Impressionists largely kept to oil on canvas, those on the periphery including Jean-François Raffaëlli were more experimental in their choice of media: his Parisian Rag Pickers from about 1890 was made using a mixture of oil paints and oil crayons.

The new generation of painters who started their careers in the early twentieth century used stick media increasingly. Egon Schiele was a prolific draftsman who used drawing techniques extensively in his painting. This work showing Krumau Town Crescent (Small Town V) (1915) is based on a drawing he had made the previous year, and uses the unusual combination of black crayon, gouache and oils.

For this Portrait of the Artist’s Wife Seated, Holding Her Right Leg, Schiele used just black crayon and gouache.

Some of the older generation joined in with unusual combinations of media. Late in his life, the former Divisionist Paul Signac painted many brilliantly coloured views of the south of France using combinations of watercolour and crayons, such as Antibes (1917) above, and The Old Port of Marseilles (1931) below.

On the other side of the Atlantic, also late in his career, Joseph Stella developed a novel drawing technique combining traditional metalpoint with modern crayons, which he used in his intimate portrait of Kathleen Millay from about 1923-24, above, and Eggplant, one of his last works, completed in 1944, below.

Metalpoint uses fine metal wire, most commonly silver, mounted in a holder, and is a slow and meticulous method of drawing or painting; its marks on paper are only faint to begin with, but they darken slowly as the fine tracks of silver tarnish.

Late in his career, Pierre Bonnard incorporated stick media in some of his paintings. The richly textured marks in this painting of his wife Marthe in The Bath from 1942 are strokes of coloured crayon, worked over gouache and pastels.

Paul Nash added both graphite and crayon marks to his 1937 watercolour of Three Rooms, a painting with strong graphic elements.

In the nineteen-twenties and -thirties, several art suppliers developed new types of crayon, using proper binders intended to allow more extensive effects and working, greater versatility, and improved longevity. These mixed conventional pigments with a bewildering array of waxes, oils and other substances, including:

• waxes and gums, to make crayons (sheathed in paper) and pencils (in wood);
• waxes, to make grease pencils;
• waxes and oils, to make lithographic crayons;
• mineral wax (paraffin), to make wax crayons;
• synthetic wax (polyethylene), to make water-dispersible wax crayons, such as Caran d’Ache Neocolor crayons;
• waxes and non-drying oils, to make oil pastels;
• waxes and drying oils, to make oil sticks and oil bars, that can form polymerised paint layers similar to conventional oil paints.

Their physical properties, determined by the binders used, in turn determine how they can be applied, appropriate grounds, fragility of the stick and its suitability for sharpening, whether diluents are organic solvents or water, and the depth and robustness of the resulting paint layer.

Unfortunately, even reputable manufacturers seem reluctant to provide detailed information on the lightfastness of pigments used, and to achieve high chroma level in attractive colours they often resort to pigments known to be fugitive on exposure to light. During the twentieth century in particular, this resulted in many fine paintings being made using media that rapidly became a conservation nightmare, either because the paint film has proved unstable, or their initially brilliant colours have faded rapidly.

Some types of media, in particular coloured pencils, have been vulnerable to irresponsible suppliers and artists who have put blind faith in products that have proved ephemeral. Sadly, few artists have obeyed the exhortation for the buyer to beware, and assessed the permanence of the media they have used in paintings which have been sold for large sums.

Among the most recent, and still unproven, media are oil pastels, which work into creamy layers, and undergo only limited hardening because they don’t incorporate drying oils like linseed or walnut. Their origins are controversial: first developed in Japan, and slightly later in Europe, it’s claimed that Pablo Picasso preferred them.

Oil pastels have certainly shown themselves capable in some unusual circumstances, such as Robert Clark Templeton’s court paintings, including his Sketch of an Overview of the Courtroom from 1971. Few courts would have even considered him using watercolours, for example, and for this case he chose modern and unobtrusive oil pastels. This sketch has been executed briskly, with effective use of gestures and marks.

Once a sketch has been laid down in oil pastels, it’s quick to work that up into a more detailed portrait like Templeton’s Drawing for CBS Evening News of Bobby G. Seale and others (1971).

Copyright restrictions prevent me from showing examples of stick media in the hands of modern artists, but I conclude by showing a couple of my own amateur efforts.

This Alpine landscape was painted in the studio using Sennelier oil pastels on Daler Rowney Ingres pastel paper.

This dawn view of the Pont Royal in the centre of Paris was painted with Caran d’Ache water-dispersible Neocolor crayons on paper. This uses base washes brought out from an initial dry crayon sketch, with superimposed texturing using dry crayon – something hard to achieve in watercolour.

Modern stick-based media look alluring, and are persuasively marketed by their vendors. However, those are seldom the traditional art materials suppliers that they might seem: most have been bought up by large companies that are primarily driven by increasing sales revenues, and may have little understanding of the requirements and problems of painting media.

Modern vendors are often secretive over the composition of their products, and although good standards exist for lightfastness, few publish data for their product ranges. Finally, their advantages in the making of art are often marred by the need to protect these paintings under glass.

The Forest of Fontainebleau covers an area of about 250 square kilometres (almost 100 square miles) to the south-east of Paris. It’s mixed deciduous woodland, much of it ancient, with a royal castle at its centre. Around the edge of the forest are several small villages that have attracted painters since the early nineteenth century, and inspired two schools of painting: Barbizon, named after the village where most of its adherents gathered, and Impressionism. This weekend I show some of their paintings, starting today with examples from the Barbizon period up to the early 1860s.

The forest has been a favourite hunting ground for French kings, and for the Emperor Napoleon.

Among the paintings of François Flameng showing the Napoleonic period, one of the most striking is this scene of Napoleon Hunting in the Forest of Fontainebleau, where the pack is closing in on a cornered stag as the sun sets.

The royal castle, Château de Fontainebleau, was later used by Napoleon III for receptions.

Jean-Léon Gérôme articulated Napoleon III’s aspirations for empire in his elaborate formal painting of the Reception of Siamese Ambassadors by Napoleon III (1864), depicting the grand reception held at Fontainebleau on 27 June 1861. Gérôme attended in the role of semi-official court painter, made sketches of some of the key figures, and was further aided by photographs made by Nadar. He also included himself, and the older artist Ernest Meissonier (1815-1891), in the painting: I believe that they are both at the back, at the far left.

Achille Etna Michallon was one of the first great landscape artists to paint en plein air in the forest. His study of The Fallen Branch, Fontainebleau from about 1816 anticipates the Barbizon School in its motif, style and location. This large branch looks more like a dying animal.

A decade later, the British artist Richard Parkes Bonington visited briefly and both sketched and painted In the Forest at Fontainebleau (c 1825). The rocks here are particularly painterly, suggesting that this may have been started, if not completed, in front of the motif.

Towards 1830, inspired by the paintings of John Constable, several young French landscape painters started visiting the forest. The first was probably Camille Corot, who first painted there in 1822, and returned in earnest in the Spring of 1829, after his long stay in Italy to learn plein air painting technique in the Roman campagna.

In Corot’s Fontainebleau Forest (The Oak) from about 1830, the twisted limbs of the oak have taken time and care, sufficient to give texture and shadows to the trunks and branches. Where the canopy is more broken he painted the leaves in considerable detail.

Corot was joined by Théodore Rousseau, Constant Troyon, Jean-François Millet, Paul Huet, and later Charles-François Daubigny and Henri Harpignies. Although many of their paintings were made in the forest, few have been located with certainty.

When Harpignies was on the edge of the Forest of Fontainebleau, he painted largely en plein air, including this fine view of Fir Trees in Les Trembleaux, near Marlotte from 1854.

The great animalière Rosa Bonheur lived on the edge of the forest, where she painted some fine watercolours, including her Deer in the Forest of Fontainebleau (1862). By that time, the next generation was getting ready to take over from the Barbizon School.

She worked in American consulates around the world but found a home in China’s “Paris of the East,” where she documented a vanishing colonial architecture.