Primary Sources A Natural History of the Artist’s Palette

For all its transcendental appeals, art has always been inextricably grounded in the material realities of its production, an entwinement most evident in the intriguing history of artists’ colours. Focusing in on painting’s primary trio of red, yellow, and blue, Philip Ball explores the science and stories behind the pigments, from the red ochre of Lascaux to Yves Klein’s blue.

July 23, 2020

chevreul colour wheel)
caption={Plate 3 from Michel E. Chevreul’s *Exposé d’un moyen de définir et de nommer les couleurs* (1861) — <a href="" target="_blank" rel="noopener noreferrer" >Source</a>Scroll through the whole page to download all images before printing.

Plate 3 from Michel E. Chevreul’s Exposé d’un moyen de définir et de nommer les couleurs (1861) — Source

Having taken many centuries to figure out what the primary colours are, we are now in the process of abandoning them. The very notion of primaries can now spark furious arguments among colour specialists. Some point out that the trio many of us learnt at school — red, yellow and blue — applies only to mixing pigments; mix light, as in the pixels of television screens, and you need different primaries (roughly, red, blue, green). But if you print with inks, you use another “primary” system: yellow, cyan and magenta. And in the rainbow spectrum of visible light, there’s no hierarchy at all: no reason to promote yellow light above the slightly longer-wavelength orange.

What’s more, even though painters learn how to mix colours — blue and yellow to give a green, say — they quickly learn that the results can be disappointingly muddy compared to a “pure” pigment with the intended colour: it’s especially hard to get a rich purple from red and blue. As a result, artists often think of colour not so much as an abstract property but in terms of the substance that makes it: madder red, ultramarine blue, cadmium yellow. To truly understand what colour means to the artist, we need to think of its materiality. Or to put it another way, what the artist’s palette is capable of producing has always depended on the materials at his or her disposal, and the ingenuity that went into procuring them.


That ingenuity has never been lacking. During the last Ice Age life was nasty, brutish and short, yet humans still found time for art. Tools dated to around one hundred thousand years ago have been found in Blombos Cave on the coast of South Africa: grindstones and hammer-stones for crushing a natural red ochre pigment, and abalone shells for mixing the powder with animal fat and urine to make a paint that would be used to decorate bodies, animal skins, and perhaps cave walls. The paintings made 15-35 millennia ago at Chauvet, Lascaux and Altamira attest to the genuine artistry that early humans achieved using the colours readily to hand: black charcoal, white chalk and ground bone, and the earthy reds and yellows of ochre, a mineral form of iron oxide.1

But the classic red pigments don’t rely on iron minerals, the hue of which is not the glorious red of a sunset or of blood, but of the earth. For many centuries, the primary red of the palette came from compounds of two other metals: lead and mercury. The pigment known as “red lead” was made by first corroding lead with vinegar fumes, turning the surface white, and then heating that material in air. It was used in ancient China and Egypt, Greece and Rome.

For the Roman author Pliny, any bright red was called minium — but by the Middle Ages that Latin term was more or less synonymous with red lead, which was used extensively in manuscript illumination. From the verb miniare (to paint in minium) we get the term “miniature”: nothing to do, then, with the Latin minimus, “smallest”. The association today with a diminutive scale comes simply from the constraints of fitting a miniature on the manuscript page.

Codex Manesse red lead miniature)
caption={Illustration for the poet Herr Kristan von Hamle (folio 71v), from the Codex Manesse, an early 14th-century poetry anthology produced in Zurich — <a href="" rel="noopener noreferrer" target="_blank">Source</a>Scroll through the whole page to download all images before printing.

Illustration for the poet Herr Kristan von Hamle (folio 71v), from the Codex Manesse, an early 14th-century poetry anthology produced in Zurich — Source

Pliny’s best minium was a different red pigment, called cinnabar. This was a natural mineral: chemically, mercury sulfide. It was mined in the ancient world, partly for use as a red colourant but also because the liquid metal mercury could easily be extracted from it by heating. Mercury was thought to have almost miraculous properties: ancient Chinese alchemists in particular used it in medicines.

By the Middle Ages, alchemists and craftspeople knew how to make mercury sulfide artificially by combining liquid mercury and yellow, pungent sulfur (available in mineral form) in a sealed vessel and heating them. This process, which was described in the craftsman’s manual De diversis artibus (ca. 1122) by the German monk Theophilus, can give a finer-quality pigment than natural cinnabar. It was a procedure of great interest to alchemists too, as the Arabic scholars of the eighth and ninth centuries had claimed that mercury and sulfur were the basic ingredients of all metals — so that combining them might be a route to making gold. Theophilus had no such esoteric goal in mind; he just wanted a good red paint.

This “artificial cinnabar” became known by the name vermilion. The etymology is curious, and shows the confusing and treacherous flux of colour terms in an age when the hue of a substance seemed more significant than vague, pre-scientific notions of what its chemical identity was. It stems from the Latin vermiculum (“little worm”), since a bright red was once extracted from a species of crushed insect: not a paint pigment but a translucent dye of scarlet colour, arising from an organic (carbon-based) substance that the insects produce.

Such dyes were also known as kermes (from the Sanskrit kirmidja: “derived from a worm”), the etymological root of crimson. Because the insects that made it could be found on Mediterranean trees as clusters encrusted in a resin and resembling berries, the dyes might also be called granum, meaning grain. From this comes the term ingrained, implying a cloth dyed in grain: the dye was tenacious and did not wash out easily. “‘Tis in grain sir, ‘twill endure wind or weather”, Olivia assures Viola of a painting in Twelfth Night.2

Red dyes were associated with majesty, opulence, status and importance: they were the colours used for cardinals’ robes. Painters needed fine reds to render on board and canvas these dignitaries whose portraits they were increasingly commissioned to paint: Raphael’s Pope Julius II (1511-12) derives its aura of power partly from the brilliance of its reds.

Raphael Pope Julius)
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Raphael, Portrait of Pope Julius II, 1511 — Source

Red lead and vermilion served well enough in the Middle Ages, but the increased demand for verisimilitude in the Renaissance meant that the orangeish hue of red lead or vermilion wasn’t adequate for depicting the purplish magnificence of these dyes on canvas. One alternative was to turn the dyes themselves into a paint pigment, by fixing their colourant molecules onto solid, colourless particles that could be dried and mixed with oils. This process involved some challenging chemistry, but even the ancient Egyptians knew how to do it. The basic idea is to precipitate a fine-grained white solid within a solution of the dye: the dye sticks to the particles, which dry to make a dark red powder. In the Middle Ages this process used the mineral alum, which can be converted to insoluble white aluminium hydroxide. The pigment made this way was called a lake, after the word (lac or lack) for a red resin exuded by insects indigenous to India and southeast Asia.

One of the best red lakes of the late Middle Ages and the Renaissance was made from the dye extracted from the root of the madder plant. As lake manufacture was perfected, artists such as Titian and Tintoretto began to use these pigments mixed with oils, giving a slightly translucent paint that they would apply in many layers for a deep wine-red tint or wash over a blue to make purple.

Aside from the creation of red lakes, rather little about the painter’s reds changed from the Middle Ages until modern times. The Impressionists in the late nineteenth century made avid use of the new yellows, oranges, greens, purples, and blues that advances in chemistry had given them, yet their reds were not really any different to those of Raphael and Titian.

It wasn’t until the early twentieth century that a vibrant and reliable new red entered the repertoire. The discovery of the metal cadmium in 1817 immediately produced new yellow and orange pigments, but a deep red was made from this element only around the 1890s. The yellow and orange are both cadmium sulfide; but to get a red, some of the sulfur in this compound is replaced by the related element selenium. It wasn’t until 1910 that cadmium red became widely available as a commercial colour, and its production became more economical when the chemicals company Bayer modified the method in 1919.

Cadmium red is a rich, warm colour — and arguably the painter’s favourite red, except for the price. That was certainly true for Henri Matisse, for who red held a special valence — as his interiors in La Desserte (aka The Red Room, 1908), Red Studio (1911) and Large Red Interior (1948) attest. Of the second of these, the art critic John Russell said “It is a crucial moment in the history of painting: colour is on top, and making the most of it.”3

Matisse Red Studio)
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Henri Matisse, The Red Studio, 1911 — Source


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The ochres used by the artists of prehistory offered them not just rusty reds but a kind of natural yellow too. This yellow ochre was, however, the hue of tawny hair and wood, and not at all the thing for tulips or an emperor’s satin robes.

Brighter yellows were, from antiquity, made from synthetic compounds of tin, antimony, and lead. The ancient Egyptians knew how to combine lead with antimony ore, and in fact a natural mineral form of that yellow compound (lead antimonate) was also used as an artists’ material. It could be found on the volcanic slopes of Mount Vesuvius, which is how it came to be associated with Naples: from the seventeenth century a yellow composed of tin, lead, and antimony was often called “Naples yellow”. Other recipes for a yellow of similar appearance specified mixing the oxides of lead and tin. The ingredients weren’t always too clear, actually: when Italian medieval painters refer to giallorino, you can’t be sure if they mean a lead-tin or lead-antimony material, and it is unlikely that the painters recognised much distinction. Before modern chemistry clarified matters from the late eighteenth century, names for pigments might refer to hue regardless of composition or origin, or vice versa. It could all be very confusing, and from a name alone you couldn’t always be sure quite what you were getting — or, for the historian today, quite what a painter of long ago was using or referring to.

In some respects that’s still true now. A tube of modern “Naples yellow” won’t contain lead (shunned for its toxicity) or antimony, but might be a mixture of titanium white and a chromium-based yellow, blended to mimic the colour of the traditional material. There’s no harm in that; on the contrary, the paint is likely to be not only less poisonous but more stable, not to mention cheaper. But examples like this show how wedded artists’ colours are to the traditions from which they emerged. When you’re talking about vermilion, Indian yellow, Vandyke brown, orpiment, the name is part of the allure, hinting at a deep and rich link to the Old Masters.

One thing is for sure: you won’t find the gorgeous orpiment yellow on the modern painter’s palette (unless perhaps they are consciously, and in this case rather hazardously, using archaic materials). It is a deep, golden yellow, finer than Naples and lead-tin yellows. The name simply means “pigment of gold”, and the material goes back to ancient times: the Egyptians made it by grinding up a rare yellow mineral. But by the Middle Ages, the dangers of orpiment were well known. The Italian artist Cennino Cennini says in his handbook Il libro ‘dell arte, written in the late fourteenth century, that it is “really poisonous”, and advises that you should “beware of soiling your mouth with it”.4 That’s because it consists of the chemical compound arsenic sulfide.

Orpiment was one of the gorgeous but costly pigments imported to Europe from the East, in this case from Asia Minor. (In the early nineteenth century there were also imports from China, so that orpiment was sold in Britain as Chinese yellow.) Such alluring imports often arrived through the great trading centre of Venice, and orpiment was hard to acquire up in Northern Europe during the Middle Ages and the Renaissance — unless, like the German artist Lucas Cranach, who ran a pharmacy, you had specialist connections to exotic materials. Some orpiment was made not from the natural mineral but artificially by the chemical manipulations of alchemists. This type can be spotted on old paintings today by studying the pigment particles under the microscope: those made artificially tend to be more similar in size and have rounded grains. From the eighteenth century it was common to refer to this artificial orpiment as King’s yellow. Rembrandt evidently had a supplier of the stuff, which has been identified in his Portrait of a Couple as Isaac and Rebecca (often called The Jewish Bride), painted around 1665.

Rembrandt Jewish Bride)
caption={Rembrandt Harmensz. van Rijn, *Portrait of a Couple as Isaac and Rebecca* (known as *The Jewish Bride*), ca. 1665 — <a href=",_genaamd_%27Het_Joodse_bruidje%27_-_Google_Art_Project.jpg" rel="noopener noreferrer" target="_blank">Source</a>Scroll through the whole page to download all images before printing.

Rembrandt Harmensz. van Rijn, Portrait of a Couple as Isaac and Rebecca (known as The Jewish Bride), ca. 1665 — Source

If Dutch painters wanted a golden yellow like orpiment without the risk of poisoning, the Age of Empire supplied another option. From the seventeenth century, Dutch paintings (including those of Jan Vermeer) begin to feature a pigment known as Indian yellow, brought from the subcontinent by the trading ships of Holland. It arrived in the form of balls of dirty yellowish-green, although bright and untarnished in the middle, which bore the acrid tang of urine. What could this stuff be? Might it truly be made from urine in some way? Lurid speculation abounded; some said the key ingredient was the urine of snakes or camels, others that it was made from the urine of animals fed on turmeric.

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The mystery seemed to be solved in the late nineteenth century by T. N. Mukharji, an author, civil servant, and curator at Kolkata’s Indian Museum. Making enquiries in Kolkata, Mukharji was directed to a village on the outskirts of the city of Monghyr in Bihar province, allegedly the sole source of the yellow material. Here, he reported, he found that a group of cattle owners would feed their livestock only on mango leaves. They collected the cows’ urine and heated it to precipitate a yellow solid which they pressed and dried into lumps.

The cows (so the story goes) were given no other source of nutrition and so were in poor health. (Mango leaves might also contain mildly toxic substances.) In India such lack of care for cattle was sacrilegious, and legislation effectively banned the production of Indian yellow from the 1890s.

There has been debate about how much of this story is true, but the basic outline seems to stand up — the pigment has a complicated chemical make-up but contains salts of compounds produced from substances in mango leaves when they are metabolized in the kidneys.

Kausa Ragaputra Indian Yellow)
caption={Ragamala Rajput painting from northern India, ca. 1700, displaying heavy use of “Indian yellow” — <a href="" rel="noopener noreferrer" target="_blank">Source</a>Scroll through the whole page to download all images before printing.

Ragamala Rajput painting from northern India, ca. 1700, displaying heavy use of “Indian yellow” — Source

Turner Teignmouth Indian Yellow)
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J. M. W. Turner, Teignmouth, 1812. One of many Turner paintings to use “Indian yellow”, but one of only a few to feature the animal whose urine lies at the centre of the colour’s legend — Source

If deadly arsenic-laden powers or cows’ urine did not appeal to artists, the choice of yellows was decidedly lacklustre — literally. There were yellow plant extracts, such as weld or saffron, that faded easily, or compounds of tin, lead and antimony with a pale, insipid quality. It’s not hard, then, to imagine the excitement of the French chemist Nicolas Louis Vauquelin when at the start of the nineteenth century he found he could make a vibrant yellow material by chemical alteration of a mineral from Siberia called crocoite.

This stuff was itself red — it was popularly called Siberian red lead, since there was truly lead in it. But in 1797 Vauquelin found there was something else too: a metallic element that no one had seen before, and which he named after the Greek word for colour, chrome or chromium.

The name was aptly chosen, because Vauquelin soon discovered that chromium could produce compounds with various bright colours. Crocoite is a natural form of lead chromate, and when Vauquelin reconstituted this compound artificially in the laboratory, he found it could take on a bright yellow form. Depending on exactly how he made it, this material could range from a pale primrose yellow to a deeper hue, all the way through to orange. Vauquelin figured by 1804 that these compounds could be artists’ pigments, and they were being used that way even by the time the French chemist published his scientific report on them five years later.

The pigment was expensive, and remained so even when deposits of crocoite as a source of chromium were discovered also in France, Scotland, and the United States. Chromium could also supply greens, most notably the pigment that became known as viridian and which was used avidly by the Impressionists and by Paul Cézanne.

The chromium colours play a major role in the explosion of prismatic colour during the nineteenth century — evident not just in Impressionism and its progeny (Neo-Impressionism, Fauvism, and the work of Van Gogh) but also in the paintings of J. M. W. Turner and the Pre-Raphaelites. After the muted and sometimes downright murky shades of the eighteenth century — think of Joshua Reynolds’ muddy portraits and the brownish foliage of Poussin and Watteau — it was as if the sun had come out and a rainbow arced across the sky. Sunlight itself, the post-Impressionist Georges Seurat declared, held a golden orange-yellow within it.

Seurat Seascape Gravelines)
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Georges Seurat, Seascape (Gravelines), 1890 — <a href=""rel="noopener noreferrer" target="_blank">Source

For their sun-kissed yellows, the Pre-Raphaelites and Impressionists did not need to rely on chromium alone. In 1817, the German chemist Friedrich Stromeyer noticed that zinc smelting produced a by-product with a yellow colour in which he discovered another new metallic element, named after the archaic term for zinc ore, cadmia: he called it cadmium. Two years later, while experimenting on the chemistry of this element, he found that it would combine with sulfur to make a particularly brilliant yellow — or, with some modification to the process, orange. By the mid-century, as zinc smelting expanded and more of the byproduct became available, these materials were offered for sale to artists as cadmium yellow and cadmium orange.

There’s a lesson in the cadmium pigments that applies to all colours, through all ages: they have often been byproducts of some other chemical process altogether, often discovered serendipitously as chemists and technologists pursue other goals — to make ointments, say, or soap, glass, or metals.

Or dyes. If you buy a tube labeled “Indian yellow” today, mangoes and cows had nothing to do with it. It probably contains a synthetic pigment that goes by the unromantic name of PY (pigment yellow) 139 — a carbon-based molecule that is one of the countless offshoots of the industry that arose in the nineteenth century to supply bright dyes for textiles. The first of these artificial dyes, discovered in 1856, was aniline mauve. A chemically related “aniline yellow” — a member of the important family of colorants called azo dyes — was sold commercially from 1863.

This manufacture of a galaxy of synthetic colours from petrochemicals seems a deeply unglamorous way to brighten the world today, compared to the age of King’s yellow, saffron, and Indian yellow. It could feel that what is saved in the purse is sacrificed in the romance. Maybe so. But artists are typically pragmatic people, as eager for novelty as they are attached to tradition. There has never been a time when they have not avidly seized on new sources of colour as soon as those appear, nor when they have not relied on chemistry to generate them. The collaboration of art and science, craft and commerce, chance and design, remains as vibrant as ever.


Blue has always spoken to something beyond ourselves: it is a colour that draws us into the void, the infinite sky. “Blue is the typical heavenly colour”, said Wassily Kandinsky in his book Concerning the Spiritual in Art (1912).5 And who would doubt it after seeing the ceiling of the Arena Chapel in Padua, painted by Giotto around 1305, a vault coloured like the last moments of a clear Italian twilight? Some cultures don’t even recognise the sky as having a hue at all, as if to acknowledge that no earthly spectrum can contain it. In the ancient Greek theory of colour, blue was a kind of darkness with just a little light added.

Virgin Mary and stars Arena Chapel in Padua Giotto)
caption={Detail featuring the Virgin Mary, from the ceiling of the Capella degli Scrovegni (Arena Chapel), in Padua, magnificently adorned with Giotto frescoes in ca. 1305. For the luminous blue throughout Giotto made use of ultramarine, which, due to its chemistry and expense, had to be applied on top of the already-dry fresco (*fresco secco*) — <a href="" rel="noopener noreferrer" target="_blank">Source</a> (Photo: José Luiz Bernardes Ribeiro, [CC BY-SA 4.0]( through the whole page to download all images before printing.

Detail featuring the Virgin Mary, from the ceiling of the Capella degli Scrovegni (Arena Chapel), in Padua, magnificently adorned with Giotto frescoes in ca. 1305. For the luminous blue throughout Giotto made use of ultramarine, which, due to its chemistry and expense, had to be applied on top of the already-dry fresco (fresco secco) — Source (Photo: José Luiz Bernardes Ribeiro, CC BY-SA 4.0)

There’s a strong case to be made, then, that shades of midnight have always been the most treasured of artists’ colours. One of the earliest of the complex blue pigments made by chemistry was virtually an ancient industry in itself. The blue-glazed soapstone carvings known now as faience produced in the Middle East were traded throughout Europe by the second millennium BCE. Faience is typically now associated with ancient Egypt, but it was produced in Mesopotamia as long ago as 4500 BC, well before the time of the Pharaohs. It is a kind of glassy blue glaze, made by heating crushed quartz or sand with copper minerals and a small amount of lime or chalk and plant ash. The blue tint comes from copper — it is of the same family as the rich blue copper sulfate crystals of the school chemistry lab, although faience could range from turquoise-green to a deep dusk-blue. These minerals were typically those today called azurite and malachite, both of them forms of the compound copper carbonate. It’s not at all unlikely, although probably impossible to prove, that the manufacture of glass itself from sand and alkaline ash or mineral soda began in experiments with firing faience in a kiln somewhere in Mesopotamia.

Similar experimentation might have given rise to the discovery of the trademark blue pigment of the Egyptians, simply known as Egyptian blue or frit. The recipe, at any rate, is almost the same: sand, copper ore, and chalk or limestone. But unlike faience glaze, this material is not glassy but crystalline, meaning that the atoms comprising it form orderly arrays rather than a jumble. Producing the pigment requires some artisanal skill: both the composition and the kiln temperature must be just so, attesting to the fact that Egyptian chemists (as we’d call them today) knew their craft — and that the production of colours was seen as an important social task. After all, painting was far from frivolous: mostly it had a religious significance, and the artists were priests.

The minerals azurite and malachite make good pigments in their own right — the first more bluish, the second with a green tint. They just need to be ground and mixed with a liquid binder. In the Middle Ages that was generally egg yolk for painting on wooden panels, and egg white (called glair) for manuscript illumination. Good-quality azurite wasn’t cheap, but there were deposits of the mineral throughout Europe. To the English (who had no local sources) it was German blue; the Germans knew it as mountain blue (Bergblau).

Albrecht Altdorfer Christ Taking Leave of His Mother)
caption={Albrecht Altdorfer, *Christ Taking Leave of His Mother*, ca. 1520 — <a href=",_Christ_Taking_Leave_of_His_Mother_(probably_1520).jpg"rel="noopener noreferrer" target="_blank">Source</a>Scroll through the whole page to download all images before printing.

Albrecht Altdorfer, Christ Taking Leave of His Mother, ca. 1520 — <a href=",_Christ_Taking_Leave_of_His_Mother_(probably_1520).jpg"rel="noopener noreferrer" target="_blank">Source

A cheaper blue was the plant extract indigo, used as a dye since ancient times. Unlike most organic dyes — those extracted from plants and animals — it doesn’t dissolve in water, but can be dried and ground into a powder like a mineral pigment, and then mixed with standard binding agents (such as oils) to make a paint. It gives a dark, sometimes purplish blue, sometimes lightened with lead white; Cennino described a “sort of sky blue resembling azurite” made this way from “Baghdad indigo”.6 As the name suggests — the Latin indicum shares the same root as “India” — the main sources for a European medieval artist were in the East, although a form of indigo could also be extracted from the woad plant, grown in Europe.

But the artist who could find a patron with deep pockets would be inclined towards a finer blue than any of these. When the Italian traveller Marco Polo reached what is today Afghanistan around 1271, he visited a quarry on the remote headwaters of the Oxus River. “Here there is a high mountain”, he wrote, “out of which the best and finest blue is mined.”7 The region is now called Badakshan, and the blue stone is lapis lazuli, the source of the pigment ultramarine.

Cennino shows us how deeply ultramarine blue was revered in the Middle Ages, writing that it “is a colour illustrious, beautiful, and most perfect, beyond all other colours; one could not say anything about it, or do anything with it, that its quality would not still surpass”.8 As the name implies, it came from “beyond the seas” — imported, since around the thirteenth century, at great expense from the Badakshan mines.

Ultramarine was precious not just because it was a rare import, but because it was extremely laborious to make. Lapis lazuli is veined with the most gorgeous deep blue, but grinding it is typically disappointing: it turns greyish because of the impurities in the mineral. These impurities have to be separated from the blue material, which is done by kneading the powdered mineral with wax and washing the wax in water — the blue pigment flushes out into the water. This has to be done again and again to purify the pigment fully. The finest grades of ultramarine come out first, and the final flushes give only a low-quality, cheaper product, called ultramarine ash. The best ultramarine cost more than its weight in gold in the Middle Ages, and so it was usually used sparingly. To paint so extensively with the colour, as Giotto did in the Arena Chapel, was lavish in the extreme.

Très Riches Heures du duc de Berry Ascension)
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Detail from “The Ascension” (folio 184r) from the Très Riches Heures du duc de Berry, ca. 1412 — Source

More often the medieval painter would use ultramarine only for the most precious components of a painting. That seems to be the real reason why most altarpieces of this period that depict the Virgin Mary show her with blue robes. For all that art theorists have attempted to explain the symbolic significance of the colour — the hue of humility or virtue, say — it was largely a question of economics. Or, you might say, of making precious materials a devotional offering to God.

You can compare azurite and ultramarine side by side in Titian’s explosion of Renaissance colour, Bacchus and Ariadne (1523). Here is that starry vault, turning to day before our eyes, and it is painted in ultramarine. So too is Ariadne’s robe, which dominates the scene. But the sea itself, on which we see Theseus’s boat receding from his abandoned lover, is azurite, with its greenish tint.

Titian Bacchus and Ariadne)
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Titian, Bacchus and Ariadne, 1523 — Source

Over the centuries, artists accumulated a few other blues too. Around 1704 a colour-maker named Johann Jacob Diesbach, working in the Berlin laboratory of alchemist Johann Conrad Dippel, was attempting to make a red lake pigment when he found that he had produced something quite different: a deep blue material. He had used a batch of the alkali potash in his recipe, supplied by Dippel — but which was contaminated with animal oil allegedly prepared from blood. The iron used by Diesbach reacted with the material in the oil to make a compound that — unusually for iron — is blue in colour. By 1710 it was being made as an artist’s material, generally known as Prussian blue.

It wasn’t entirely clear what had gone into this mixture, and so for some years the recipe for making Prussian blue was surrounded by confusion and secrecy. In 1762 one French chemist declared that “Nothing is perhaps more peculiar than the process by which one obtains Prussian blue, and it must be owned that, if chance had not taken a hand, a profound theory would be necessary to invent it.”9 But chance was a constant companion in the history of making colours. At any rate, Prussian blue was both attractive and cheap — a tenth of the cost of ultramarine — and it was popular with artists including Thomas Gainsborough and Antoine Watteau. It comprises some of the rich blue Venetian skies of Canaletto.

Canaletto Piazza San Marco)
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Canaletto, Piazza San Marco, ca. 1725 — Source

Another blue from the Renaissance and Baroque periods went by the name of smalt, which is not so very different from the cobalt-blue glass of Gothic cathedrals such as Chartres, ground to a powder. Its origins are obscure, but may well come out of glass-making technology; one source attributes the invention to a Bohemian glassmaker of the mid-sixteenth century, although in fact smalt appears in earlier paintings. Cobalt minerals were found in silver mines, where their alleged toxicity (actually cobalt is only poisonous in high doses, and trace amounts are essential for human health) saw them named after “kobolds”, goblin-like creatures said to haunt these subterranean realms and torment miners. Natural cobalt ores such as smaltite were used since antiquity to give glass a rich blue colour, and smalt was produced simply by grinding it up — not too finely, because then the blue becomes too pale as more light is scattered by the particles. As a result of its coarse grains, smalt was a gritty material and not easy to use.

Some art historians make no distinctions between this “cobalt blue” and those that were given the name in the nineteenth century. But the latter were much finer, richer pigments, made artificially by systematic chemistry. In the late eighteenth century the French government asked the renowned chemist Louis-Jacques Thénard to look for a synthetic substitute for expensive ultramarine. After consulting potters, who used a cobalt-tinted glassy blue glaze, in 1802 Thénard devised a strongly coloured pigment with a similar chemical constitution: technically, the compound cobalt aluminate. Cobalt yielded several other colours besides deep blue. In the 1850s a cobalt-based yellow pigment called aureolin became available in France, followed soon after by a purple pigment called cobalt violet: the first ever pure purple pigment apart from a few rather unstable plant extracts. A sky blue pigment called cerulean blue, a compound of cobalt and tin, was a favourite of some of the post-Impressionists.

La Gare Saint Lazare Claude Monet)
caption={Claude Monet, *La Gare Saint-Lazare*, 1877 — <a href="" rel="noopener noreferrer" target="_blank">Source</a>Scroll through the whole page to download all images before printing.

Claude Monet, La Gare Saint-Lazare, 1877 — Source

But what artists craved most of all was ultramarine itself — if only it wasn’t so expensive. Even by the mid-nineteenth century it remained costly, which is why the Pre-Raphaelite Dante Gabriel Rossetti caused much dismay (not to mention added expense) when he upset a big pot of ultramarine paint while working on a mural for Oxford University.

By Rossetti’s time, however, artists did at last have an alternative — it’s just that several of them had not yet learnt to trust it. As chemical knowledge and prowess burgeoned in the early nineteenth century, bringing new pigments such as cobalt blue onto the market, it seemed within the realms of possibility to try to make ultramarine artificially.

It was a prize well worth striving for, because pigment manufacture had become big business. The manufacture of colours and paints wasn’t supplying artists; there was now a taste for colour in the world at large, in particular for interior decoration. Factories were set up in the nineteenth century to make and grind pigments. Some sold them in pure form to the artist’s suppliers, who would then mix up paints for their customers from pigment and oil. But some pigment manufacturers, such as Reeves and Winsor & Newton in England, began to provide oil paints ready-made; from the 1840s these were sold in collapsible tin tubes, which could be sealed to prevent paints from drying out and could be conveniently carried for painting out of doors.

Winsor and Newton paint tubes)
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Pages from a Winsor & Newton catalogue, ca. 1895 — Source

Mindful of the importance of the pigment market, in 1824 the French Society for Encouragement of National Industry offered a prize for the first practical synthesis of ultramarine. It is a complicated compound to make — unusually for such inorganic pigments, the blue colour comes not from a metal but from the presence of the element sulphur in the mineral crystals. This composition of ultramarine was first deduced by two French chemists in 1806, offering clues about what needed to go into a recipe for making it. In 1828, an industrial chemist named Jean-Baptiste Guimet in Toulouse described a way to make the blue material from clay, soda, charcoal, sand and sulfur, and he was awarded the prize (despite a rival claim from Germany). In England this synthetic ultramarine was subsequently widely known as French ultramarine, and Guimet was able to sell it at a tenth of the cost of the natural pigment. By the 1830s there were factories making synthetic ultramarine throughout Europe.

Artists looked upon this substitute with considerable caution, however. Ultramarine still retained some of its old mystique and majesty, and painters were reluctant to believe that it could be turned out on an industrial scale. Perhaps the synthetic variety was inferior — might it fade or discolour? Actually synthetic ultramarine is (unlike some synthetic pigments) very stable and reliable, but J. M. W. Turner was evidently still wary of it when, in the mid-century, he was about to help himself to the ultramarine on another artist’s palette during one of the “finishing days” at the Royal Academy, where artists put their final touches to paintings already hung for display on the walls. Hearing the cry that this ultramarine was “French”, Turner declined to dab into it.

But by the end of the century, synthetic ultramarine was a standard ingredient of the palette: small wonder, given that it could be a hundred or even a thousand times cheaper than the natural variety. Synthetic ultramarine is the pigment in Yves Klein’s patented International Klein Blue, which he used for a series of monochrome paintings in the 1950s and early 60s. But ultramarine never looked like this before — at least, not on the canvas.

Yves Klein blue IKB 191)
caption={Yves Klein, *IKB 191*, 1962, one of a number of works Klein painted with International Klein Blue — <a href="" rel="noopener noreferrer" target="_blank">Source</a> (Not public domain)Scroll through the whole page to download all images before printing.

Yves Klein, IKB 191, 1962, one of a number of works Klein painted with International Klein Blue — Source (Not public domain)

Klein noticed that pigments tend to look richer and more gorgeous as a dry powder than when mixed with a binder — another consequence of how light gets transmitted and refracted — and he sought to capture this appearance in a paint. In 1955 he found his answer in a synthetic fixative resin called Rhodopas M60A, made by the Rhone-Poulenc chemicals company, which could be thinned to act as a binder without impairing the chromatic strength of the pigment. This gave the paint surface a matt, velvety texture. Klein collaborated with Edouard Adam, a Parisian chemical manufacturer and retailer of artists’ materials, to develop a recipe for binding ultramarine in this resin, mixed with other solvents.

Even in the modern era, then, some artists were still depending on chemical assistance and expertise. Despite the profusion of new pigments with complicated and recondite chemical formulations, the intimate relationship of painters to their materials has not been entirely severed.

Philip Ball is a freelance science writer and broadcaster. He worked previously at Nature for over 20 years, first as an editor for physical sciences and then as a Consultant Editor. His writings on science for the popular press have covered topical issues ranging from cosmology to the future of molecular biology. His books include Bright Earth: The Invention of Colour (Penguin, 2002), Invisible: The Dangerous Allure of the Unseen (University Of Chicago Press, 2015) and most recently, How To Grow a Human (William Collins, 2019).

The text of this essay is published under a CC BY-SA license, see here for details.